Poor idle in gear, continued

[jsgold]

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?

[Joshua M. Smith]

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 <><

[Cailen]

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.

[jsgold]

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.

[Cailen]

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.

[jsgold]

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.

[Cailen]

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.

[jsgold]

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.

[jsgold]

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.

[jsgold]

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.

[Joshua M. Smith]

Originally Posted by jsgold

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 <><

[BlazerBoyLT98]

Originally Posted by Joshua M. Smith

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

[jsgold]

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?

[BlazerBoyLT98]

Originally Posted by jsgold

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

[Joshua M. Smith]

Originally Posted by BlazerBoyLT98

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 <><