Hello Usa!

I just got home from the garage where I am rebuilding a 87 vette.
I have encountered a problem regarding the ignition timing. This is what happend:
The idle has ben unusually high (1200rpm), engin backfires and my exhaustmanifold were glowing. I thaugt it might have something to do with the ignition timing. So i disconnected the brown and black wire and loosened the screw for the distributor. I saw that the ignition was Off the scale! I turned the distributor so that the marking was set on 6 degree ptdc. the vette runned exellent and i took her for a ride. I was very happy until I got back and turned the engine off and started it again. The idle was high again and the ignition was once again off the scale. I turned off the engine, disconnected the brown and black wire again... But I couldnt get the marking back to 6 degrees!!! Even before I got the marking back ON the scale it missfired and died... This made me very confused and I thaugt I´d seek some expert advise on this before I start to change all the sensors and computerboxes again...

Have a nice spring!
/The Swede :confused: :confused:

 

I have an '84 and at least on that year GM used a damper (with the timing mark) with poor quality. In mine the outer ring had moved so the timing mark was 6 degrees off with no visible damange to the damper. This problem is not uncommon. I don't know what years are affected but the '87 might be too.

This could explain the problem wiht setting the timing, but it still should run good once set even if the timing mark is off. You could have some problem with the reference pickup in the distributor.

 

1) Howdy!

<Do you have any way of checking your ALDL stream? In not, you haev access to a multimeter/test meter/volt meter?>

2) You are correct in that incorrect ignition timing can cause the glowing. I have had glowing when the ignition timing is incorrect and also when I was running too rich (excessively rich...the computer couldn't remove any more fuel than it was removing).

3) You trying tomake us think? That is not allowed :D Actually, you set timing correctly, or at least it appears so. Was the engine warm when you originally set the timing? When you disconnected the wire (I'll call it the EST bypass), what was the RPM? Approximate coolant temp? Engine run time? Ambient temp? I assume that ptdc was meant to be BTDC.

4) When you said the ignition was off the scale, had you also disconnected the EST bypass wire or had you kept it connected this time? If you kept the wire connected, then it would be different. You probably know that, but just covering all the bases here.

There is a possibility that your harmonic balancer (the hub that has the line on it that you are reading ignition timing with) is slipping. Here is a quick way to check. Get out some white paint or ink-correction fluid. Make a thin line on the balancer and also on the pulley that is on the outside of the harmonic balancer. The pulley is bolted to the inside of the hub. Nothing is bolted to the outside. If your balancer is slipping, then after you run the car, the line that you just drew will no longer match up. If your balancer is slipping, you will likely benefit from a new one. If your balancer is slipping, then you are actually not going to be able to set timing correctly with the stock markings.

I have a few routines that I try to keep. One of them involves the following: Any time I adjust timing, I also reset my idle air control (IAC) valve. There is a tech tips article on this forum regarding resetting the IAC. I also disconnect the battery to clear whatever the computer felt like keeping in memory.

If it is sensor related, the first one that comes to mind is the coolant temp sensor. It is not the same sensor that feeds your gage.

5) I'm gonna try. I have the week off (from school--not from work) so hopefully I can get my car back on the road again!

Good luck, -Matt

 

1) Hi Again
2)How can I check if it is running too rich?? Couldn´t this also cause the high idle? Will the cpu not compensate the exessfuel with more air? =higher idle?
3)yepp, the engine was warm, rpm when disc wire was approx 800rpm. coolant temp was 90-100 degrees Celsius, ptdc=btds
4)the wire was disconnected.

Now to another question... when u flash the pulley it is very hard to see the marking. the only marking I see is a "cut" in the pulley where it passes under the sawtoothed scale... There are no other markings at all on the pulley so it has to be that one but it seemes very stupid to put it there because u can barely see it when passing under the sawtoothed scale...

The most annoying :banghead: thing is that i have never done this on a corvette before so I really dont know what the marking looks like.

I really apprechiate your help guys!!!!

Toggy
:banghead:

 

2) Could be. When I was running too rich, my IAC counts went full open and I got a pretty bad "vacuum leak". Vacuum went from 16 in-hg to about 10 at the same RPM in drive. TO check rich/lean without a scanner, you might do a search on the forum for "Field Service Mode".

5) There was only one cut on my balancer. I filled it in with white paint too.