1998 gmc with 454. Rebuilt 30k miles ago. Every sensor has been replaced. Keeps burning #5 and 7 wires at the plug and now it is burning 1 and 2. Diagnostic said timing is off by 26 degrees. No vacuum leak. It has new intake gaskets. New distributor. So what do I change next?
Burnt plug wires
- Thread starter Dollars78
- Start date
zora
Staff member
- Joined
- Apr 24, 2012
- Messages
- 5,519
- Reaction score
- 139
- Points
- 63
Does this engine have the stock exhaust manifolds?
Are these the original spark plug wires?
If not, what brand of wires are they?
Not clear how an engine that is 26 degrees off timing would continue to run.
Please describe in detail how this was determined?
Are these the original spark plug wires?
If not, what brand of wires are they?
Not clear how an engine that is 26 degrees off timing would continue to run.
Please describe in detail how this was determined?
zora
Staff member
- Joined
- Apr 24, 2012
- Messages
- 5,519
- Reaction score
- 139
- Points
- 63
I asked questions about the plug wires.
Are they touching the exhaust manifold?
Replace them with a new set of AC-Delco wires or other brand name set but do not use a cheap set.
Do you have a check engine
light on and if so what are the codes?
The person who ran the diagnostic had no idea why the timing was retarded?
Are you sure the timing wasnt 26 BTDC?
Are they touching the exhaust manifold?
Replace them with a new set of AC-Delco wires or other brand name set but do not use a cheap set.
Do you have a check engine
light on and if so what are the codes?
The person who ran the diagnostic had no idea why the timing was retarded?
Are you sure the timing wasnt 26 BTDC?
It's not the plug wires.
It is 26 atdc.
The only code is for the egr which it doesnt have.
And nobody I have talked to or had work on it has any clue why it would do this. I am a very good mechanic but I'm down to changing out the timing chain and/or the cam. I've replaced everything I can possibly think of and still dont know what it is.
It starts and idles fine but when it is warm and in gear it idle hunts between 500-1000 rpms. The intake is clean. It has passed a smoke test. All new plugs and plug wires correctly installed. New manifolds. All the best product. New injectors as well. Complete fuel system all new.
I had originally had an issue with a high idle. I replaced the intake gaskets and replaced the iacv. That fixed the idle but then it started melting the plug wires about every 2 weeks or 500 miles.
It is 26 atdc.
The only code is for the egr which it doesnt have.
And nobody I have talked to or had work on it has any clue why it would do this. I am a very good mechanic but I'm down to changing out the timing chain and/or the cam. I've replaced everything I can possibly think of and still dont know what it is.
It starts and idles fine but when it is warm and in gear it idle hunts between 500-1000 rpms. The intake is clean. It has passed a smoke test. All new plugs and plug wires correctly installed. New manifolds. All the best product. New injectors as well. Complete fuel system all new.
I had originally had an issue with a high idle. I replaced the intake gaskets and replaced the iacv. That fixed the idle but then it started melting the plug wires about every 2 weeks or 500 miles.
Last edited:
zora
Staff member
- Joined
- Apr 24, 2012
- Messages
- 5,519
- Reaction score
- 139
- Points
- 63
An engine wont run at 26 ATDC and curiously the 26 BTDC number is what you would get with the computer plugged in using a timing light above 1k rpm. Have you looked into whether your harmonic balancer outter ring has slipped? Another thought is the computer is not advancing the timing.
A timing chain shouldn't go in 30k and a cam problem would cause noisy lifters.
I know the plug wires arent responsible for the reading, your telling me they are burning, and I'm asking you about the quality of the wires.
A timing chain shouldn't go in 30k and a cam problem would cause noisy lifters.
I know the plug wires arent responsible for the reading, your telling me they are burning, and I'm asking you about the quality of the wires.
zora
Staff member
- Joined
- Apr 24, 2012
- Messages
- 5,519
- Reaction score
- 139
- Points
- 63
Not sure how much experience you have on pre-computer engines but as you start retarding timing say from 8 BTDC down to 2 BTDC at idle the engine RPM starts dropping to the point of almost stalling. As you increase RPM on a mechanical advance distributor the advance can add 26 degrees to the initial setting, so getting a reading of 26 ATDC, exact opposite of what is expected, just doesn't make sense.
Right. And that is why I am here trying to find someone that can explain it. So far nobody I have talked to in person Or on any forum can give me an answer.
And all of my experience is with pre computer cars. I restore studebakers so I figure this has to be something electronic but I have spent hours tryi.g to trace it down and cant find. The only thing I havent replaced is the ecm, timing chain and I havent had a chance to check the harmonic yet.
And all of my experience is with pre computer cars. I restore studebakers so I figure this has to be something electronic but I have spent hours tryi.g to trace it down and cant find. The only thing I havent replaced is the ecm, timing chain and I havent had a chance to check the harmonic yet.
zora
Staff member
- Joined
- Apr 24, 2012
- Messages
- 5,519
- Reaction score
- 139
- Points
- 63
You said it was overhauled 30k ago, very doubtful on chain. You can also check the chain by pulling the plugs, inserting a piston stop in number 1 cylinder hand turn engine till you touch stop note position of timimg mark relative to damper, rotate opposite direction and recheck mark, should be the same within 3 to 5 degrees. Did you carefully check the electrical connections to the distributor. There maybe two connectors, one of which is the ECM connection
That is great advice. I will do that. Thank you.
And yes we checked the wiring but couldn't find anything. I was debating on checking again but the mechanics said he thinks its mechanical not electronic. I am having him replace the ecm now since I dont have the computer to reset it.
And yes we checked the wiring but couldn't find anything. I was debating on checking again but the mechanics said he thinks its mechanical not electronic. I am having him replace the ecm now since I dont have the computer to reset it.