firered89

well, i finally called a shop, and im going in tomorrow morning. he said more thank likely, its something very minor and he would have to drive it to tell. i hope all goes well. he also said if it happens more when your going up hill, its probably your spark plug wires...this might be my case...ZT.

ffp444

I DON'T KNOW IF YOU ARE STILL HAVING THIS PROBLEM, SEEING THAT YOUR POST WAS IN MAY. HOWEVER, I WOULD LIKE TO HELP. I HAVE A 97 Z-71 WITH 5.7. I INSTALLED A NEW GM CRATE MOTOR IN 10/04. SEVERAL MONTHS LATER, I BEGAN TO HAVE A MISSFIRE IN CYLINDER 8 AND 6. CYLINDER 8 MISSFIRE WAS CONSTANT, WHILE CYLINDER 6 WAS JUST EVERY ONCE IN A WHILE. THIS PROBLEM WOULD ONLY OCCUR AFTER THE ENGINE WARM-UP PHASE. THE ENGINE RAN PERFECT WHILE COLD. I WAS ALSO HAVING AN OIL CONSUMPTION PROBLEM. I PULLED ALL OF THE SPARK PLUGS TO FIND THAT 6 AND 8 WERE OIL AND FUEL SOAKED. A COMPRESSION TEST REVEALED 6 AND 8 WERE LOWER THAN THE OTHER CYLINDERS, BUT THEY WERE STILL IN SPEC. WHILE REMOVING THE INTAKE MANIFOLD, THE BOLT CLOSEST TO 6 AND 8 CAME LOOSE WAY TO EASILY. ONCE I REMOVED THE INTAKE, THE GASKET AROUND 6 AND 8 HAD BEEN PULLED DOWN BY ENGINE VACUUM SECONDARY TO THAT LOOSE BOLT. THIS ALLOWED FOR THE MISFIRE IN THOSE 2 CYLINDERS WITH 8 BEING THE WORST. THIS ALSO EXPLAINED THE OIL CONSUMPTION BECAUSE OF THE GAP CAUSED BY THE DISPLACEMENT OF THE INTAKE GASKET. I BELIEVE THAT THE EXPLANATION OF THE ENGINE ONLY MISFIRING WHILE WARM: WHILE COLD, THE INTAKE SITS FLAT ON THE GASKET, CREATING A GOOD SEAL. UPON WARM-UP, THAT ALUMINUM EXPANDS AND CAUSES A GAP, ALLOWING CONDITIONS FOR A MISFIRE. MY SOLUTION: WHEN I INSTALLED MY CRATE MOTOR,
I WAS VERY PRECISE WITH MY TORQUE SPECS, BEING A FORMER BMW MASTER TECH. HOWEVER, WHEN I TORQUED MY INTAKE BOLTS, I USED JUST WHATEVER LOCTITE I HAD IN MY TOOL BOX. I BELIEVE THIS IS WHY THE BOLT BACKED OUT. BE SURE TO USE THE APPROPRIATE HIGH TEMP LOCTITE SO THIS DOES NOT RE-OCCUR AND OF COURSE, TORQUE TO PROPER SPECS IN A STAR PATTERN. HOPE THIS HELPS.

kcb37

dartlord2001
What did the first set of plugs look like when you pulled them? I only ask cause it seems like you have done everything you can and should have fixed this by now. But if you have 1 cylinder with a particularly bad set of rings it may be fouling out the plugs, and if one is bad the rest will surely follow suit. Have you done a compression check yet. I can't remeber for sure but I think they should each be within 10 psi of each other.

chevyblues

This is a reply to the start of the thread.

My '95 Z-71 is having similar problem. Runs ok, but lacks a little power, until warmed up good. Then has very poor acceleration and sometimes feels like it is even missing. I too suspected EGR valve or EGR solenoid. EGR valve holds vacuum with engine off, but doesn't hold with engine on. The lines hold vacuum all the way to the EGR valve. I replaced both the EGR valve and the EGR solenoid. Nothing changed. It was also overheating a bit with the A/C turned on. For grins, I changed the thermostat and the fuel filter. Doesn't overheat any more but still have the power problem.

The only thing I have been able to do to get the engine to run ok again was to disconnect the vacuum line to the EGR Solenoid and plug it.

chevyblues

dartlord2001

Hey
This is the one that posted the orig. thread. as I said before,I had a guy check my truck with a scanner and he found no problems.I found an advance auto parts with an OBD I scanner.They checked it and their scanner showed a code 42.The printout says Ign System problem-Elec spark timing circuit fault.They said a knock sensor could cause this but they didnt know that for sure.My Haynes manual says knock sensor problem would be code 43.I have tried to locate the elec spark control on the motor but I cant find it.The Haynes manual shows it right by the TBI on the right side but its not there on mine.I cant find the 4 wire plug for it either.Is anyone familiar with this?The truck is a '94 W/5.7L
Thanks

chevyblues

I have a Chilton (8055) 28624 for 1988-98. The illustration and description put the knock sensor on the block to the front of the starter motor. There some testing instructions. If I had a scanner, it would be yours. Basically it says, you can check the time with timing light and then tap on the front of the engine block. Timing should retard. If not there is a problem with the sensor or the circuit. If replacing, the installation needs to be done to not insulate it from the block.

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chevyblues

bradstump

I had the same problem with a '96. after warming up, it would miss, spit, and sputter under acceleration. Mine was fixed with a fuel filter. Believe it or not, it started again about 3 weeks later. I replaced it again and it never acted up again. I figure I got some bad gas and it just stopped it up.

99Silverado

My just off the showroom (used showroom of course) 99 Silverado has what appears to be the same miss. Only mine is all of the time, not just after warmup. One comment I haven't heard on this thread is if anyone is getting a warning light. I am getting a "Service Engine Soon" light. Autozone checked it tonight and they tell me I need a new catylitic converter. Has anyone replaced theirs? Has anyone removed the cat. conv. where there is no exhaust requirments? There are none in my suburb of Memphis. I don't know if the computer will run without it.

99Silverado

I recently put this on its own post but someone didn't like it I guess and got deleted. But this forum is dead. I'm not getting any hits off this and I get more than I need on my FTE forum!

harmongreer

i am having the same problems too.


91 chevorlet 5.7 v8

it starts missing from 1700 rpm to 2900 rpm


I need help!