Poor idle in gear, continued

Sorry to start another thread on this, but felt it was needed. LT had been suggesting the truck might have CPI trouble (may be right) however after further tests I am not so sure. At least I want to rule out other stuff just in case. If I have to replace the CPI fine, I can do it. My troubles all started back in December. My 93 S-10 (4.3 VinW) had started stalling for long periods of time. It finally let go where I could not work on it and I had a fellow that works on our GM trucks look at it and turned out to be igntion module. It would rarley stall in gear when idleing, usually when in a tight turn in a parking lot or such. When I asked him about it you stated that the truck needed to relearn idle and not to worry about it. Started happening more often, was told maybe the IAC was failing. I checked over and found wires pinched under cap, loose vaccum line and loose cap to boot (one screw not tightened tight). The wires and the loose screw did not affect it and the vaccum line fix did help but it made me wonder if he rushed the job (during Xmas season, and he WAS covered up) and the truck did not act up for a couple of weeks. Then started oh so rarley stalling in tight situations in idle. FIgured I would wait til it was warm and dig deeper rather than take it back. I have run checks on fuel pressure, replaced all tune up items including o2 sensor, and so far no luck. truck idles Ok when in park, but will stall out in anywhere from 10-20 sec in gear. Ditto with AC. Idles at 650 in park, 600 in gear. When I loosen a vacuum line little and "fool" it into idleling at say, 700-750, won't stall. Of course I can't run it like this. I checked and thought I saw fuel per LT's advice when checking the plenum under the Vortec plate/valve, but after using a MUCH better light and a lot of probing I found small trace amounts of pil, not gas. Do not see where the regulator was leaking, and while I see a small "clean" area on passenger side, I am not convinced it is anything yet to go on. Checked with fuel on, no signs of anything. My pressure starts at 60, then drops to 58 after 2 sec, then runs at a steady 54+ lbs. No blled off I can detect. It could still be a CPI problem, however with the history I still wonder if the job was rushed and possibly the timing was not done right. may be weak link. but have not been able to check as of yet. The IAC is new, replaced it a while back... EGR was cleaned, no affect (not dirty) No trouble codes ever given until I changed O2 and the truck picked that tine to run like crap for 5 min and set a code indicating a rich contion. Nothing more since, truck runs well on road, gets 20-21 mgp combined hwy and city. I have a scan tool, do not see anything out of sorts. Any ideas?

With it idling, hold a piece of paper near the exhaust pipe. Report back if it's being sucked back in now and again.

Josh <><

So aside from a "small" area on the passenger side of your manifold that was washed, underneath the plenum is completely blackened and carbonized? It should be REALLY dirty in there. How did the driver's side look?

Fuel pressure (I believe) is supposed to be up and around the 64psi range, and driveability issues start at 60.

Any odor when truck is at operating temperature?

Just bite the bullet and pull the plenum off man.

The fuel pressure is right on according to the GM service manual, however let me add a couple of other bits of information. When the ignition module first showed itself the condition fooled me as I could get the truck to hit on starting fluid when it would stall out, so I had a new fuel pump put in, as that seemed the logical thing to do according to a local mechanic who I thought was knowledgable.(not thrilled about working with gas tanks either) I had never worked with a Vortec motor and had little knowledge of it, plus, I did not own a fuel pressure tester. A very expensive lesson to learn. I now own one and the original readings I got were 60 at key "on", dropped to ZERO. Ran at a bouncy 53-54. Replaced the filter, tried again. 60 at key on, dropped to 30, ran at 54-55. based on these it seemed that yes, perhaps there was a pressure problem. Again, though, I am decent at a lot of mechanic work like brakes, water pumps and so forth. But, never used a fule pressure tester before. I tested it again the other evening and got 60, then dropped to58. Idles at 54-55, when throttle applied it jumps to 60+ per the GM service manual. It states that it should be 60-64 on key on and then drop slightly when relay kicks off in 2 sec. Should run at idle at 54-56. Should jump to 60+ when throttle engaged. Does this pretty much as it should. My concern is why did I get such different readings, a bad regulator, pump, or did I not have the tester installed properly, perhaps not screwed down enough. I would guess it is one of three things, see what you folks think. Possibly the regulator/CPI, possible goofy fuel pump, or, perhaps the fellow who installed the distributor did not TIME it right, and that may be a reason for weak idle. I am going to take random readings on the pressure during the next few days and see how they compare. I do not own a timing light so that is something I will have to get. The fuel pump I do not see as bad, but, I cannot assume anythng at this point. The random stalling in idle on started after the fuel pump and the igniton module was installed (same week). I suppose the CPI could be the problem with all I have read, but, it seems a bit on coincidence that I should investigate first before spending $300. The spot I reffered to is not golden "washed" as I would think it would be if raw gas was being put on it, and the regulator shows no leakage areas that I can see. But your are right, looks like I may have to pull the plenum to be sure. I just want to see aht else it could be based on the previous work done on it. The truck seems to run and idle welll until it is in gear, or has A/C on. Idles OK then poof, off it goes. Pressure does not drop when this happens. Will take random tests during the next 2-3 days and try the tailpipe test as well.
PS - The drivers side looked dirty and dark. No signs of wash at all. I have owned this truck 2 yrs, do not have ANY idea what was done to it before. It had 65K on it when I bought it, now has 100K. For all I know it has had this done years ago. Problem with owning an old truck.

Keep doing your readings then. Between this thread and your other one several people have offered you advice that you don't want to listen to.

By the by, stalling issues would occur regardless of your being in park or drive if something were wrong with your timing. But no one is going to convince you, so hear what you want to hear and have your timing checked.

As well if you're going to do Joshua's test accurately you'll need to do 4-5 trials of about 30 seconds each. Remember to key on key off before each trial. It will be most accurate if you can have someone to start your vehicle for you so that you can be at the tailpipe when it starts.

With it idling, hold a piece of paper near the exhaust pipe. Report back if it's being sucked back in now and again.

Please do not misunderstand my concerns. I am always welcome to ideas on these troubles. And I always try to give advice on the things I AM familiar with. My concern is that the main thing everyone jumps on is the CPI on these trucks. When I had trouble with this truck months ago, that was the advice then as well as fuel pump. Was not it. Was ignition module. My truck runs pretty well except at idle and then it simply shuts off at differerent times, usually when in gear for a while, or slowing down and turning off the road. Random at that. The reason I asked about timing was to get more opinions as I would think that perhaps if it was off slightly it would cause the motor to be possibly "weak" at slower RPM. I will continue to try any ideas given me. I am going to run a series of tests on the fuel pressure this evening( as you listed) and for the next 2-3 days. Also will try the paper test to see if it shows anything.I remember people doing that in the 70's. Removing the plenum is not something I am looking forward to, but, if no other explanations make any sense I will remove it Saturday or Sunday and see what gives. Thanks for your input. It IS appreciated along with all others. Let's face it, it is hard to totally diagnose these things without seeing them , hearing them ,or driving them. Thanks again to all.

Yeah I understand the concern about people just recommending something without giving a problem much thought. Do your due dilligence and you won't end up throwing parts at your truck.

The truck is cooling down a bit so I can start fuel pressure tests. Tried the paper test and what found is that it did try to suck the paper in twice during a 2 minute try. Do not know if that means anything for sure. The truck will occasionally mis fire which is not helping it's cause any. Will hit and miss. Runs with no miss for several revolutions and then "pop" it misfires and it seems to do this pretty often. Has never been perfect but I know it should not be mis firing. I have read that these trucks have a history of less than perfect idles. For the most part the paper simply moved away with each exhaust stroke, but when it tried to pull the paper in it surprised me. Did not do it the last minute or so. One other note- the entire distributor was replaced when ignition module failed. Not just the module so I know it had retimed after it was worked on. Will continue with pressure tests and advise later on.

Forgot to mention. as far as smells go, I have always thought that this truck burned a bit rich due to the smell, but nothing horrible. I changed out the plugs 2 weeks ago and the old ones showed failry clean except for some minor white deposits.

Tried the tailpipe test again, as was suggested with 6 periods of 30 sec. Had my son start the truck. was not able to get it to pull the paper in, except when shut off (did it every time was turned off, but that may be normal). No change in fuel pressure. Starts at 60 lbs, drops to 58 and stays there. According to Blazee's CPI wirteup that seems in line. Will try again shortly and let it sit for 5-6 minutes and see if any dropoff. Unsure how much longer I can try this as it should drop off anyway after a while I think.

OK, here is fuel pump measurements. At 5pm I got the same as before, shoots to 60lbs when key on, drops to 58, idled at 54. I tested several times this evening. Kicked up to 62 with key on, dropped to 59, ran at 54. Interesting in that instead of dropping over time the pressure acutally rose a little. When the relay licked off after 2 sec the pressure rose from 59-60. when I ran it at 54 lbs it rose to 56 after being shut off. I "think" that is because the regulator does not actually control the pressure until the engine runs, IF I read that in the manual. It still may or may not mean anything. if nothing else it was different than last three levels, although only by 1-2 lbs. The engine will uncork a miss as I stated before, maybe that is the problem. Something is causing an occasional miss that may be enough at low idle to stall it. Guess the injector assy is looking more and more like the culprit. Even if it is not pouring fuel into the plenum, perhaps 1-2 of the poppets are screwed up?? The fuel pressure does drop after about 3 minutes at the rate of 1lb every 2 min. with no power at all. I suppose it will leak off eventually on its own.

Advise please. thanks.

Tried the paper test and what found is that it did try to suck the paper in twice during a 2 minute try. Do not know if that means anything for sure. The truck will occasionally mis fire which is not helping it's cause any. Will hit and miss. Runs with no miss for several revolutions and then "pop" it misfires and it seems to do this pretty often. Has never been perfect but I know it should not be mis firing. I have read that these trucks have a history of less than perfect idles. For the most part the paper simply moved away with each exhaust stroke, but when it tried to pull the paper in it surprised me. Did not do it the last minute or so.

That, sir, is at least part of your problem. The paper being sucked in is indicative of a sticking exhaust valve. On the intake stroke it will sometimes pull exhaust back into the cylinder. This does two things:

First, the mixture is weakened by the exhaust and may not ignite. Dependent upon how strong your exhaust flow is, this may force exhaust gas back up through the intake manifold/plenum. I would only expect this at idle.

Second, you have a specific way your exhaust is set up. One cylinder lets its exhaust out, then the next one does the same thing. A bit of negative pressure should exist between the first and second pulse (etc etc so on and so forth). This allows the first pulse to "pull" the second pulse along creating a smooth exhaust flow.

You can always try dumping in a can of oil detergent or engine flush, but I'm not a fan of this stuff.

As to your other problems... you can try this as long as you understand there is a chance, VERY small mind you, but the chance is there, that you will hydrolock the engine:

Take a can of Berryman's B12. Find the vacuum hose closest to the intake. Pull it out and dip it into the B12. Pull it back out before the engine dies. Repeat until about half the can is gone. When half the can is gone, dip the hose in and let it kill the engine. Let the beast sit for 15 minutes to 1/2 hour. Start it up and rev. Watch the soot come out your tailpipe - this was solid carbon in your motor prior to beginning this exercise. Repeat, remembering to pull out when the engine threatens to die, until the can is gone.

I've done the Berryman trick to scores of engines and I've never hydrolocked one. I think that the risk of hydrolock is more theoretical than actual because, unless you use a huge hose, there shouldn't be enough sucked in to do any damage.

Choice is yours sir, but I would recommend it. I do refuse to be held liable however should your engine be damaged.

Josh <><

That, sir, is at least part of your problem. The paper being sucked in is indicative of a sticking exhaust valve. On the intake stroke it will sometimes pull exhaust back into the cylinder. This does two things:

First, the mixture is weakened by the exhaust and may not ignite. Dependent upon how strong your exhaust flow is, this may force exhaust gas back up through the intake manifold/plenum. I would only expect this at idle.

Second, you have a specific way your exhaust is set up. One cylinder lets its exhaust out, then the next one does the same thing. A bit of negative pressure should exist between the first and second pulse (etc etc so on and so forth). This allows the first pulse to "pull" the second pulse along creating a smooth exhaust flow.

You can always try dumping in a can of oil detergent or engine flush, but I'm not a fan of this stuff.

As to your other problems... you can try this as long as you understand there is a chance, VERY small mind you, but the chance is there, that you will hydrolock the engine:

Take a can of Berryman's B12. Find the vacuum hose closest to the intake. Pull it out and dip it into the B12. Pull it back out before the engine dies. Repeat until about half the can is gone. When half the can is gone, dip the hose in and let it kill the engine. Let the beast sit for 15 minutes to 1/2 hour. Start it up and rev. Watch the soot come out your tailpipe - this was solid carbon in your motor prior to beginning this exercise. Repeat, remembering to pull out when the engine threatens to die, until the can is gone.

I've done the Berryman trick to scores of engines and I've never hydrolocked one. I think that the risk of hydrolock is more theoretical than actual because, unless you use a huge hose, there shouldn't be enough sucked in to do any damage.

Choice is yours sir, but I would recommend it. I do refuse to be held liable however should your engine be damaged.

Josh <><


That is a pretty neat trick, where did you learn that? Also what are the other draw backs to doing this? What are the other things that let's say he screws up can go wrong? Is there another, maybe safer way to fix his issue? And also, to get this done by a mechanic, what would your estimate be for the cost? Thanks

Berrymans not well know here, but I see NAPA and Advance carry some of it nationwide, so I can get it one way or the other. the question I have is that there is a number of the B12 products according to their website, so, which product are you recommending? I see at least 5 different products that are B12. Also, I saw a method someone listed either here or the S-10 forum that mentioned spraying water into intake while running. Actually a mist from a spray bottle, that was to clean out carbon. Have you used this of Marvel Mystery oils in this way?

Berrymans not well know here, but I see NAPA and Advance carry some of it nationwide, so I can get it one way or the other. the question I have is that there is a number of the B12 products according to their website, so, which product are you recommending? I see at least 5 different products that are B12. Also, I saw a method someone listed either here or the S-10 forum that mentioned spraying water into intake while running. Actually a mist from a spray bottle, that was to clean out carbon. Have you used this of Marvel Mystery oils in this way?

I persoanlly really like Mystery Marvel oil. I have never used it in the Crank Case but I have used it in the gas. On this site there are numerous refrences on how to flush your engine a little differently then how the bottle of engine flush says too. I tried and my truck has never run better, although I was not having quite the issue you were. Do a search for engine flushing and let me know what you come up with. If you have trouble I will retype the directions on how I did it and how my oil came out super hot and jet black and well some what chunky, but it worked! Good luck

That is a pretty neat trick, where did you learn that? Also what are the other draw backs to doing this? What are the other things that let's say he screws up can go wrong? Is there another, maybe safer way to fix his issue? And also, to get this done by a mechanic, what would your estimate be for the cost? Thanks

Hello, I had a Jeep CJ5 and a Buick Regal at that time. The Regal needed cleaned out and some old mechanic told me the trick. It worked, and it's worked ever since.

I'm aware of no other drawbacks. I wasn't even told of the hydrolock situation; it's just one that makes sense. If you're going to be drawing liquid into your engine be prepared for hydrolock. As I said, it's more theoretical. My CJ5 I used to have had a Holley (among lots of other cool gadgets) and its needle seat failed. I was still running with gasoline dripping from my sidepipes. I'm surprised it didn't hydrolock then, wow!

The only other way I would know is have the engine torn down and cleaned out. This does include the heads and would most likely result in the rebuilding of the top end of his motor. I charge $20 per hour + parts (and I don't make any money off the parts). I could do the job well and right in five to eight hours. That comes up to $100 - 160 in labor alone. That's me. Now you take it to a traditional shop (which I no longer operate), you go to $40 - $50 / hr, more than double what I charge. Assume $400 in labor, a week long stay, and be charged double for parts. Probably looking at $500 - $600 all told.

Josh <><

Berrymans not well know here, but I see NAPA and Advance carry some of it nationwide, so I can get it one way or the other. the question I have is that there is a number of the B12 products according to their website, so, which product are you recommending? I see at least 5 different products that are B12. Also, I saw a method someone listed either here or the S-10 forum that mentioned spraying water into intake while running. Actually a mist from a spray bottle, that was to clean out carbon. Have you used this of Marvel Mystery oils in this way?

Hello,

The second one down, in the cylindrical can: http://www.berrymanproducts.com/Default.aspx?tabid=140

http://www.berrymanproducts.com/Portals/0/BPI%20IMAGES/0116-LR.jpg

15oz pour in.

Hope the image link works.

Josh <><

I was speaking with a friend of mine the other day about stuff along this line. I know personally I'm not a fan of these types of products because I ended up blowing a head gasket about a month after using something along these lines for a Trans Am I had.

Our discussion was about using water to do what you guys are talking about. He said that if added when the engine is stone cold water can be completely harmless, and steams away the carbon in there.

What do you guys think of that?

Someone posted this not too long ago, trying to find it. Seemed to make sense as it basically "steamed" the carbon off. So far I can't find the B12, no one knows what I am asking about at Advance, even though they are listed as a distributor. Our Advance stores here do not stock a heck of a lot. Perhaps NAPA will have it. The valve problem makes some sense to me as the truck has a minor problem with valve seal leakage on startup and has some valve chatter at times. Plus, I saw the paper twice sucked into the pipe. Could not duplicate it last night after the first two times but got dark on me. Will keep on looking into both of these ideas, and have not ruled out the plenum coming off yet. Am getting my work area ready just in case.

Someone posted this not too long ago, trying to find it. Seemed to make sense as it basically "steamed" the carbon off.
http://www.automotiveforums.com/vbulletin/showthread.php?t=283211&highlight=water+clean

Thanks. I missed this one. Another person had posted one in which they used a spray bottle. But this would work as well. Might give it a try and see what happens.

Well I did the water cleaning this morning per Blazer LT post. Some difference noticed as far as performance and a little quieter, but still stalling when idleing in gear for a while. What it was doing today was idleing well when you first stop at a traffic light, say, 10-15 sec, then it would suddenly sputter and try to stall, catch itself and rpms would zoom up then settle back OK for 8-10 sec., then shuts down just like someone turned off ignition. Came home and it stalled as I was stopping to make a turn. It has seemed to stall more when stopping and turning at closed throttle. It will idle all day at 625-650 rpm as long as it is in neutral or park. But in gear or with A/C on it drops to 600 and usually won't run for more than 15-20 sec. at idle. Have been times early in the morning it idles with no problems all the way to work, but that is rare. Does idle smoother it seems. I recall Blazer LT saying his 95 4.3 idled at 700rpm. If mine could idle that speed I bet it would not be stalling. The service manual never says what preffered idle speed IS, only refers to preffered idle speed. Seem to recall it has to idle <800 to avoid transmisson problems. Will be working some more with it Sunday I guess.

SeaFoam (NAPA) and GM Top Engine Cleaner (dealer) are two other products that will decarbon your combustion chambers. You use them similarly to that described above.

Thanks, I was looking at the Seafoam just yesterday but was unsure if it would help. Will pick up a can and try that as well. I cannot find anyone carrying the B-12.

Do it as far from civilization as possible. The smoke is really obnoxious. Take it out on the expressway for a while and run it for a while at expressway speeds in a lower gear. Let the engine rev and clean it all out.

Interesting development this morning, but unsure if it helps a lot. I was testing the truck with my scan tool to d/v voltage and some other things when I noticed the truck had set a code 35.(IAC error). First code I have seen so for except for the system rich caode I got after installing new O2 sensor. Since the IAC is new I doubt if it was bad, but it is a clue anyway. So far this morning the truck is not stalling in gear, but will be driving it to test some more. Brian, which method were you referring to on the Seafoam? Blazer LT's or Josh's?

Joshua M. Smith's method. Although I prefer a funnel and pouring it in slowly rather than sucking it in as he suggested.

I don't see any description on how to do it by BlazerLT...

When's the last time you did a tune up? I can't find that anywhere on this thread. Recommend doing so before you go spraying anything in to the engine.

If you haven't read the stickied tune up thread you should do so. Your problems could be as simple as a clogged $2 pcv valve

Just did a major tune up withih the last 3 weeks, hoping that would be it. Plugs, wires, cap, rotor button, O2 sensor, fuel filter, air filter, EGR valve cleaning, new EGR gasket, PCV valve, PCV grommet, IAC cleaned, (later replaced, hoping that the idle problem was that), throttle cleaned. I get 20+ mpg combined in town and road, and truck seems to do well except it just seems to shut itself off when idleing in gear for anything over 10-15 sec. Sometimes shuts down when stopping. Today it seems to be idleing a little rougher than yesterday, but, had not shut down after 4 tries. AM getting ready to take it out on the road to try it at normal driving speeds. Maybe the water cleaning broke some carbon loose. Will advise further.

Frastrating. Runs like a scalded dog on the highway, possibly better than ever, but shut down on me in driveway when i got back. i stopped and let it idle in gear in driveway with scan tool still hooked up and watched. You can feel it while it starts out fine, rpms at 600-625 then boom - it shuts off like someone throwing a switch. I do not see anything on the scan tool that is odd but the IAC counts seem low to me at times. I did notice the voltage on this truck is not what it should be according to service manual. I always thought on a 12 volt system it should be 12-13+, book says 14-15 volts. When the truck was cold it was putting out 14-14.5 volts, with an occasional drop for maybe a sec. to 13.8. When hot it stays at 13.5-13.7. No difference when giving it the gas. I am using my scan tool for this as I have never trusted my POS volt meter in the truck. It shows over 16 volts almost always. Possible problem here perhaps.

You did clean the hole where the IAC goes, right? I use a brush from a gun cleaning kit. These are bronze.

I'm almost wondering if your IAC isn't being restricted somehow.

You're lucky though; my Blimmy's flywheel somehow stripped and I'm out of transportation right now. :rolleyes:

Josh <><

Very possible. guess I will look into cleaning further and seeing about any other possibilties. Do not know if the voltage would do this, but, that seems possible with other threads I am reading. Sorry to hear about your truck. Would hate to have to deal with a flywheel, that sounds like more trouble than I would want to deal with.

1) Locate new flywheel

2) Undo torque converter bolts

3) Unbolt tranny and move it back

4) Unbolt flywheel

Installation is the reverse of removal.

That's the nice thing about having an apprentice though; I can just supervise :)

Don't worry about your truck; we'll get it going right. I really hate long distance diagnosis. Not tryin' to brag, but I believe if I were able to take a looksee at it, the problem would be gone after I (or most any other tech here) was done.

Just be very careful not to screw up the threads on the IAC port.

Josh <><

Well did the Seafoam thing. I am sure my new neighbors were not thrilled by this as yes, it stinks! Did it twice and then took it to the interstate to blow it all out. Seems to idle a bit smoother than before but still stalls at idle. You can actually "feel" the engine getting weaker when in gear(most of the time) and can almost time when it's going to stall. Simply shuts off. Would suggest that either fuel is dropping off or maybe something else maybe not holding??. The counts when in idle is 7-10 (IAC) and goes to 14-17 when in gear/idle. I am going to pull off the IAC and check for obstructions, and the EGR (again) in case the water cleaning and Seafoam has loosened some crud. Can't say enouigh how it runs on the open road though. I had put a cold air intake in awhile back, more for the better protection of the filter than the old leaky stock one. Really goes and sounds good for an old "plain jane" truck.