95 5.7 Problems

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ptrac

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Hey guys,
I am new to your fourm so bear with me please. I am having some major problems with my 95, let me start by telling you it has a random miss. some time 1 cyl. some times it feels like 4. Ihave replaced withinlast year, cat.conv. maps,egr.wires.plugs,tps.intake temp sensor. o2, fuel pressure reg. I am at a loss, after 35 plus years of working on Chevys I am wooped with this one. The miss is so random that if fools me to thinking its fixed......Any feed back is welcomed.
 

95slowhoe

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Have you checked the timing. The tbi 350 will miss fire randomly if it is to far advanced.
 

ezdaar

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What is your plug gap?
A weak coil and improperly gapped plugs is #1 reason for random missfire..

On ALL of my "legacy" Chevy motors I instantly replace the pickup coil in distributor, primary coil, and wires with MSD parts. along with standard copper NGK plugs gapped at 40.
 
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ptrac

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Have you checked the timing. The tbi 350 will miss fire randomly if it is to far advanced.

Thanks, timing seams to be ok but I will check again.

---------- Post added at 07:27 PM ---------- Previous post was at 07:24 PM ----------

What is your plug gap?
A weak coil and improperly gapped plugs is #1 reason for random missfire..

On ALL of my "legacy" Chevy motors I instantly replace the pickup coil in distributor, primary coil, and wires with MSD parts. along with standard copper NGK plugs gapped at 40.

i will try the coils, plugs are e3's gaped at .40....Thanks
 

retorq

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When it's missing is it throwing a code?? I don't see a TPS sensor on that list of stuff that was swapped. That was one of the first things that went on mine ... WAY before I changed many of those other things you listed.
 
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SunlitComet

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get yourself a obdI code reader, plug it in, it will trigger your dash light to help narrow thing down could also use the key method too with a jumper wire. Lots of help from everyone here.

In the meantime here is something to add from the others:

Cuts Out, Misses


SYMPTOM DEFINITION:
Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The exhaust has a steady spitting sound at idle or low speed.

PRELIMINARY CHECKS

* Refer to Diagnostic Notes. See: Computers and Control Systems\Testing and Inspection\Flow of Diagnosis\Diagnostic Notes
* If there is spray from only one injector on a TBI system, then, there may be a malfunctioning injector assembly, or in the signal to the injector assembly. The malfunction can be isolated, by switching the injector connectors. If the problem remains with the original injector, after switching the connector, the injector is defective. Replace the injector. If the problem moves with the injector connector, the problem is an improper signal in the injector circuits. Refer to "Chart A-3." See: Computers and Control Systems\Testing and Inspection\Diagnostic Trouble Code Tests and Associated Procedures\Related Tests and Information

IGNITION SYSTEM
Check:

* For cylinder miss by:

1. Start engine, allow engine to stabilize then disconnect IAC motor. Remove one spark plug wire at a time, using insulated pliers. NOTE: Do not perform this test for more than 2 minutes, as this may cause damage to the catalytic converter.
2. If there is a rpm drop, on all cylinders, (equal to within 50 rpm), go to "Rough, Unstable Or Incorrect Idle, Stalling" symptom. Reconnect IAC motor with ignition "OFF."
3. If there is no rpm drop on one or more cylinders, or excessive variation in drop, check for spark, on the suspected cylinder(s) with J 26792 (ST 125) Spark Tester or equivalent.
4. If no spark, refer to Ignition System.
5. If there is spark, remove spark plug(s) in these cylinders and check for:

o Insulation cracks.
o Wear.
o Improper gap.
o Burned electrodes.
o Heavy deposits.
o Spark plug wire resistance (should not exceed 30,000 ohms), also, check rotor and distributor cap.
o If the previous checks did not find the problem:
o Visually inspect ignition system for moisture, dust, cracks, burns, etc. With engine running, spray plug wires with fine water mist to check for shorts.

FUEL SYSTEM
Check:

* Fuel pressure. Refer to "Chart A-6." See: Computers and Control Systems\Testing and Inspection\Diagnostic Trouble Code Tests and Associated Procedures\Related Tests and Information\Chart A-6 Fuel System Diagnosis
* For contaminated fuel or restricted fuel filter.

ENGINE MECHANICAL
Check:

* For proper valve timing, low compression, bent pushrods, worn rocker arms, broken or weak valve springs, worn camshaft lobes.
* Intake and exhaust manifold passages for casting flash.
 

gulleyman

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x's 2 on checking the compression, that's what my random misfire turned out to be. I replaced a LOT of parts trying to figure it out, it would misfire on 5 and 7, then after the RPM's were over 1500 they would come back and I would lose 6.
Two mechanics looked at it and said the compression was fine, then a third found zero compression on 6. Suspected cause is a burnt exhaust valve, but we'll find out for sure when it get's rebuilt, hopefully this week.
There's a great deal of help on this forum, good luck with yours :D
 
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ptrac

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When it's missing is it throwing a code?? I don't see a TPS sensor on that list of stuff that was swapped. That was one of the first things that went on mine ... WAY before I changed many of those other things you listed.

No code, that is what is blowing my mind, I was told today that e3 plugs are great but have been having a lot of issues.
 

96ProCompTahoe

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No code, that is what is blowing my mind, I was told today that e3 plugs are great but have been having a lot of issues.


I've heard both ways with the E3's. i just use the AC delco plugs in mine.
 

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