1994 5.7 engine running rough

Recently blew a head gasket, motor started to run rough at this time. Replaced with new heads, engine still runs rough but no spark knock as it was with blown gasket. It is also running full rich and fouling plugs immediately. Cannot find standard timing wire disconnect to set base timing. I found tan wire with black stripe but no disconnect. This motor was in top notch shape, I don't know what to check next. Please help. Wife says can't spend anymore money on it. Someone mentioned O2 sensor and limp in mode for computer.

the wire is located either under the dash near the glovebox or on the firewall. make sure the distributor cap& rotor and wires are in good shape. a scan tool would be nice to check the sensors the throttle position sensor(tps) engine coolant temp sensor, knock & map sensors can all make an engine run like crap. other things to check are the egr valve and fuel pressure regulator. try unhooking the egr vacuum line and plugging it.

Thank You, yes I did check with scan tool it says no codes but reading rich. I assume all my sensors are working. Also, cap, wires, plugs and rotor are all new...I will go under the dash this afternoon and look for the t/b wire, under the hood the wire runs all the way from the distributor to the computer, but no disconnect anywhere so I will look for that. Do you think I could have blown something out when the head gasket went bad? It just seems like I've been battling two problems from the beginning. Your input is appreciated--Thanks

Fuck man I'm having troubles with my 92. When it's warmed up it'll rev fine and everything but if i'm in gear and it gets to higher rpms, say above 3500(no tach) it acts like it's cutting out or soemthing and WILL NOT accelerate so i just have to let it shift and keep on my way, it's like if it's underload it doesn't wanna go, first gear like this is terrible and I cant figure it out. My only idea right now is that it's plugs and wires, the wires are shitty and i think they're stock and with 130,000 miles, and the plugs are over 50,000. Hopefully new MSD wires and Splitfires help though. No check engine light either and it sounds normal at idle...

Edit: could it be like the fuel pump, maybe not getting enough fuel at the higher rpms or something??

your overreving on cold motor is probly your clutch fan . My 94 does this for half mile or so then is cool but it rvs like you say whn its cold

Split fire plugs are a joke. The do NOTHING to help the truck run. While at a GM Training school they had set up 5 different plugs on a spark testing bench. And while testing the split fire plugs there is only 1 spark at a time. NOT 2 like the adds say. Remember the path of least resistense that is where the arc is going to go
Sounds like you need a good tune up using ac Delco plugs and a very good set of wires, dist cap/ rotor , fuel filter, Throttle body cleaning.

Split fire plugs are a joke. The do NOTHING to help the truck run. While at a GM Training school they had set up 5 different plugs on a spark testing bench. And while testing the split fire plugs there is only 1 spark at a time. NOT 2 like the adds say. Remember the path of least resistense that is where the arc is going to go
Sounds like you need a good tune up using ac Delco plugs and a very good set of wires, dist cap/ rotor , fuel filter, Throttle body cleaning.

Well the odds are growing less in favor the Splitfires then, I'm sorry I've had one guy come up to me and tell me they were awesome and one guy said he noticed no difference so I figured I'd see for myself. I dont really care if there are 2 sparks or not I was just going to buy them from Wal Mart(cheap) and that's the best they have. I already ordered wires, they are MSD Heli Core 8mm so I'm pretty sure they're a decent wire. Um...i'm prob gonna run some fuel injector cleaner but i just looked at them the other night and they seem pretty good and it was reving just fine at the time but i did go and take the cover off, i'm not sure what it's called, some sort of chamber?? and i cleaned it out pretty good with q-tips. Cap and rotor will be changed eventually, i'll try the plugs and wires and if it's satisfactory then i'll leave everything alone otherwise the fuel filter would be my last resort cuz i wouldn't expect them to just plug up like that, it wasn't something that was slowly progressing it just kind of started happening in the past week.

I found bt wire by the computer COOL!!! set timing .also scaned again & found no codes.The scaner did say the o2 sensor was lazy??So now i bought new o2 sens & fuel filter to put on tomorrow.It is running better but still has a miss.Thanks for the help so far guys!

I forgot what year they started the using the vortec motor. But if you have one I'd be looking at the spider injector system if I were you. I've already replaced a couple on the vortecs. If it still has the throttle body nevermind :dupe: <---that guys cool
-Paul

I think my problem was just simply a mechanical one with that flap in the intake that lets warm air in from the manifold. It was stuck shut so all the air was coming from the manifold and no outside air, opened and shut it a few times to make sure it would open on it's own and it runs fine now, but the tune up is still gonna take place.

Oh and I think they started usin the Vortech heads in 96.

I give up !!!!!!!!!!!!!!!!all sensors are good. fuel is good. timing is dead nuts. I have 1,400 bucks into this blown head gasket & it still has a nasty miss!!!!!The only thing i can do now is go back & readjust all the valves again!!!!!!!!!I was confident they were right when we set them but i checked everything else at least 3 times.I even sprayed carb cleaner around the manifold & the throtle body to chk for vacume leaks.nun were found Please HELP the next thing I do is to take this thing to the FORD dealer to trade it in on somthing that can be worked on .This fucker has stumped 2 master wrenches & 1 chrysler proving ground wrench.Wife is tired of drivin me around for parts & help.I love my chevys but I need somthing that is reliable.Tha :banghead: nx guys.....

Lets take a step back away from the truck. Ok deep breath now exhale. I know when at the shop there where times I want to rip mh hair out because of a problem I could not find. This always helped me. Start from scratch. You said it was running fine before it blew a head gasket right.
I cant remember if the 94 had the TBI set up with 2 injectors.Does it . Next check the ign wires and nake sure they are not crossed (we all have done that at 1 time). Drivers side cylinders 1,3,5,7. Pass side 2,4,6,8. GM 5.7 fireing order 1,8,4,3,6,5,7,2. Its easy to cross them in a rush. if that is all ok we need to pin point what cylinder is out to lunch or if it a rich mixture or lean mixture missfire.
If you have a helper that you trust try this. Block the wheels all 4 is best. Put ebrake on open hood and stand to the side fender. Start truck and put into gear with there foot on the brake pedal.Incress engine rpm to about 2000 while keeping other foot still on the brake pedal. This is call power brake the engine load test. Now your part is to remove 1 spark plug wire at a time and check for any rpm change or and incress in the engine miss. If that cylinder does have a rpm change and a slight incress in the miss reinstall the plug wire and move on to the next 1. Keep doing this untill you find 1 that has no or very little change in rpm and or the miss. I would do all the cylinders just to make sure that there is not more then 1 problem. post back or pm me what you find and we will move on from there

Hey man, dont give up yet. The scan tool can be your best friend when looking for a misfire. If your sensors are good and your ignition is new, your fuel pressure is right and you have no vacuum leaks. I would try getting a new PROM chip. Computers arent perfect and they can go just the same as an engine part could. If your injector driver values get messed up your injector pulse wil be wrong causing a missfire at idle, but smoothing out at higher RPM's. THis is a rare case but if your running out of options and you've replaced all there is to replace and you still have a misfire, the computer isnt a bad place to try. I new PROM chip is anywhere from 80-130 bucks from www.tbichips.com. The only reason im bringing this up is because im having a misfire problem and the PROM is what is causing it.
-Paul

OK guys I double ckd all wires & firing order.Did like you said & pulled 1 wire at a time .#1 cyl did make a slight change so I readjusted valves on left side, which was a very slight adjustment. So is #1 out to lunch, it sure doesn't seem to be. motor still has a miss. TBI does have 2 injectors, they seem to be flowing good, I checked them with a timing light and a small flashlight. There seems to be a nice cone shaped spray, no drips. I was leaning away from a bad computer for the simple reason that it communicated well with the Snap On diagnostic scan tool. Once the truck is warmed up, scan tool says it's switching back and forth between lean and rich. Don't know what this means. Your help is greatly appreciated.

Please post the scan tool data engine cold first start up and engine warm we will find the problem

Ok guys you wanted it, you got it, Snap On scan tool results. First let's go thru everything cold on left column and hot on the right column:
One thing on the time columns the truck did stall twice so I don't know if the 4.30 is right or not.
RPM: 1000------------------------------------------ 725
MV: 978---------------------------------------------872
fuel trim: 128----------------------------------------131
open/closed loop:open-------------------------------closed
lt trim:126-------------------------------------------96
exhaust O2: lean-------------------------------------rich/lean
trim cell :18------------------------------------------18
knock: no--------------------------------------------no
knock retard :0---------------------------------------0
base pw/ms:3.6--------------------------------------1.3
tps voltage: .58---------------------------------------.58
O2 cross count: 0-------------------------------------5
throttle percentage: 0---------------------------------0
iac position: 116---------------------------------------53
iac direction:rev---------------------------------------rev/for
iac coil a: on/off---------------------------------------off/on
iac coil b: on/off---------------------------------------off/on
desired idle: 900---------------------------------------675
coolant: 71F------------------------------------------181F
time:2 min 5 sec--------------------------------------4 min 30 sec(??)
prom id: 8135------------------------------------------8135
map("Hg): 13.8----------------------------------------12.1
map V: 1.96-------------------------------------------1.68
barometer V: 4.78-------------------------------------4.96
barometer ("Hg): 29.2----------------------------------30.1
battery V: 14.3----------------------------------------14.1
fuel pump V: 14.3--------------------------------------14.1
CCP selenoid: off---------------------------------------off
CCP duty cycle: 0-------------------------------------0
spark adv: 20------------------------------------------23/15
accel enrich: no----------------------------------------no
decel enlean: no----------------------------------------no
power enrich: no----------------------------------------no
egr selenoid: off-----------------------------------------off
egr duty percent: 0--------------------------------------0
egr position: 0------------------------------------------0
desired egr percent: 0-----------------------------------0
vehicle speed: 0-----------------------------------------0
a/f learned :no-------------------------------------------yes
I hope this makes sense to you, let me know what you think. :screwy:

read this site
http://www.gnttype.org/techarea/faq/BLMINT.html
about long and short term fuel trim
lt trim:126-------------------------------------------96
that is not a good reading
fuel trim: 128----------------------------------------131
a little high reading
looks like its running rich and the ecm is trying to lean it out

Layman's terms please...I read the information and it just scares me. New computer, new truck, what's your opinion?

Sad to hear a Chevy not feeling well. Obviously something ain't stirring the kool-aid!!! As I was reading your problem(s) you talked about going through everything one last time, including the valves. Well, I totally believe you have analyzed everything outside the motor (like sensors, timing, plugs, wires, vac lines, fuel, etc.) more than a million times. Also believe what you say is true, all that is good. But I don't recall you mentioning double checking the valves except for #1 cyl. You spoke with much confidence about adjusting them correctly. Don't let that confidence get in your way, thats how people fail at things. Not saying you fail and not trying to insult your skills in any way. Just trying to keep you from buying one of them Ford or Mopar things. Start from scratch. These heads you put on came from where? Are they rebuilt, new, or what? Are you absolutely sure thier integity is godd? This would include everything being perfect, like the valve adjustments. Once you can check that all off as perfect (again), then you atleast have a solid foundation to build on. At which point you can check all the external factors for thier integrity since you appear to be excellent at! Your computer is a good possibility, however, start from the bottom up (again) first. In other words, build up on your solid fondation. Computers are very rarely go out. As with all the external stuff to check, I don't really have any suggestions that you haven't aleady checked....4 times! I'm a paint and body guy, not a tecnician (mechanic). However, I do have a strong mechanical apptitude and I will say it sounds like you're on the right track. You're simply forgetting to take a deep breath and walk away. Take a break and rlelax a lttle bit. The answer will dawn on you evenyually. Good luck, keep us posted. And anyone with GOOD RELATIVE suggestions help this guy out.

wowowoowo hold the phone m8s
You said it ran ruff when the head gasket blew, right ? And it still runs bad. Ok with the fuel trim readings I can see its rich while the ecm is trying to lean it out. How fast does the o2 swing from lean to rich and does it go just under and over 500 or a big swing. Check the o2 sensor pull it out and look at it because it might be fouled with antifreeze. Also the engine vacuum is low should be about 20hg at idle you have 13.1 hg on the scan tool I would put a true vacuum gauge on a main vacuum and get a reading. The low engine vacuum could be the result of misadj valves or could be the result of the main problem. Before you pull the valve covers please check the o2 with you eyes. If its white or dark black replace it it should be a brownish tan color. You might have more then 1 problem so we must look at 1 area at a time

So far, the BLM long term fuel adjustment sounds exactly like what's going on. The buick website you sent me to says to remove vacuum from fuel pressure reg. My truck has throttle body with fuel reg built into it not sure but I have to look and see how many vacuum lines are on mine. O2 sensor is brand new as are heads, plugs, wires, cap, rotor, map & fuel filter. I did say I readjusted valves on left but found adjustments so slight not worth doing the right side. I think that resetting the BLM or ECM is the way to go. When I start the truck it runs perfect for 8 seconds then starts to run rough. Thanks, we're getting close. I didn't really want a Ford anyway, I just figured it would generate some good reading.

http://www.customefis.com/GMEFI.html
read this

Think I would afree about a few different issues causing all this drama. Good to hear you're getting close. You've heard the expression "Good thing come to those who wait"

http://www.customefis.com/GMEFI.html
read this
OK, enough I'm not a college student, I have no need or use for all of this information. I don't need to understand fuel management and how computers work. I just asked if you knew how to reset the Chevy fuel ecm. You guys have given me a lot of good information but I've been tinkering on this truck for three months and I'm done. I'm going on Monday to buy a new computer for it, found one for $109, that's a lot cheaper than the data computers that the article you sent me to read told me to get. Sorry I'm not a rocket scientist, no problems if it doesn't work I'll just unload it and drive my '83 that hasn't ever let me down becuase there's no f****** computer in it. Again, you have all helped me quite a bit, just not the answer that I needed. I use robotics and lasers at work everyday and they make more sense than this website did.

http://www.customefis.com/GMEFI.html
read this

Added that site to my "Favorites."
Thanx for it.
RR

First of all, where did you find an ecm for $109? Recon thats used, sure its good, is there a warranty? Not trying to piss you off, just trying to prevent you being pissed off if you buy and doesn't do you any good 'cause its defective or something. As far as resetting your ECM, you can simply disconect your battery for 30 to 90 seconds for it to reset. Sometimes ECM's will have a reset button as well (underneath) but don't recall ever seeing one on a full size Chevy, just on s-10's and other vehicles. Also, if you have access to a scan tool, can't you reset it with that? Never used one myself but would kinda make since if you could. Sorry if this doesn't help you either. Hope you get it runnin top notch soon

Thanks for your help. This ecm is brand new but I get jobber price cuz my friend is a county fleet wrench & parts guy wants to keep him happy!! GOOD FOR ME !! Full price was still only200.bones . Auto value in Jackson mich.Also I did unhook ecm and it didnt make a dif last wk.Hopfully will get it installed by wed night I will post what happens good or bad.What about eliminating all the computer shit altogether?? Ive been told its no big deal but dont know for sure.

Well tried new ecm & nothing changed still has a miss !!Have about 1600 bones into it now guess Ill have to bite the bullit & take it to the dealer.Scan tool said all sensers are working but still switches from lean to rich back & forth when its warm.

BAD HEADS!!!! New wrench pulled heads & found a NASTY loose valve guide .Sent them to mach shop found ALL springs were junk First set they sold me were vortec WRONG!! second set are JUNK Beware of this bs head company Moore cyl headsSo far theyve screwed me for about 2000 bones in parts & labor.Oh yeh the second set had stainless valves in one head & standard in the other .No wonder all my electrical problms couldnt be solved BECAUSE the heads were the problem all along