1994 5.7 engine running rough

[acewelderman]

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.

[amac209]

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.

[acewelderman]

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

[v10_viper]

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??

[acewelderman]

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

[Fireplug]

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.

[v10_viper]

Originally Posted by Fireplug

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.

[acewelderman]

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!

[NY_Z28Man]

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 <---that guys cool
-Paul

[v10_viper]

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.

[acewelderman]

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 nx guys.....

[Fireplug]

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

[NY_Z28Man]

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

[acewelderman]

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.

[Fireplug]

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