Knocking/Pinging with my 84 CFI

[elkabong]

Howdy Gents,

I have this nagging issue with my 84 CFI pinging/knocking during acceleration. I have replace the knock sensor, oxygen sensor, cap, rotor and ignition module and I am running 91 octane fuel. The timing is sitting at 2 degrees BTDC presently. I have checked the EGR valve and it seems to be operating properly. Funny thing is I am getting code 42 "ECM Bad or replace ignition module". When I set the timing I make sure to disconnect the EST before checking/adjusting. I am a bit perplexed on this. Any thoughts from the 'wise ones'.

One perplexed guy.

 

[c4ever]

First off ,I'm pretty sure base timing is 6degrees BTDC. I had a slight detonation problem with the 85 and turned out to be in the fuel delivery system. I would do a fuel pressue test and see where she runs at idle and under load. I have my new hi pressure regulator set at 42 lbs at idle and no more detonation. With my new fuel pump put in today she running like she just left the showroom Worth a check IMHO.

Carlo

 

[VetNutJim]

The 84 TBI Fuel Injection is a low fuel pressure system.
TPI came out in 85 that uses 40~ +/- lbs of fuel pressure.

Since the 84's have such low compression to start with I doubt you're getting knock from carbon buildup.

You may want to check your total spark advance and see what you've got there. I don't remember exactly but I think 40 degrees is about the maximum advance you want.

Another thing that can cause pinging is the driving style.
Low RPM lugging the engine can contribute to pinging.

I run 93 octane in my 84 and my 91.
My 8:1 compression 350 truck engine will ping like crazy on 89 octane fuel. 91 isn't too far above 89.
You might try some octane booster ot try to find some higher octane fuel and see if that helps.
Good luck with it.

 

[JoBy]

Your base timing might not be what you set it at. The harmonic damper was bad quality those years and it is not uncommon that the outer ring moves compared to the crank. On my 84 the TDC marking on the damper was 6 degrees off then I replaced it. No visible damage to it.

 

[elkabong]

I posted the same issue on the CFI forum and it was mentioned that the harmonic balancer may be culpret. The car has 32k and I am having a hard time with this. Is there an easy way to check without taking it off the motor?

This problem also just showed up one day which is the mysterious part. My fuel pump is a new '85 pump but I have checked the pressure yet. I also read on the CFI forum that it may be a vacuum leak which is causing a lean conditon. I have sprayed carb cleaner around the manifold gasket top plate but the rpms at idle did not increase. I may just put in a new gasket. From what I gather this is also another common problem. Their is a slight surge in rpms at idle. Another indication of a vacuum leak or lean condition.

Thanks for the suggestions.

 

[elkabong]

Well here it goes. The fuel pressure is @ 17#'s and the timing is set back to 6degrees. I am still perplexed about the code 42 "Bad ECM/change ingnition module". I checked/replaced what I could knock sensor, EGR, O2 Sensor, Cat, manifold gaskets, tb gaskets .......... I hate to admit this but I gave up and took it to my local Chevy dealer. They are stumped as well and have had it for 3 days. They started out telling me that it was carbon build up. My response was 'I doubt it' for two reasons 1) The low mileage and 2) if it was carbon build up wouldn't the engine diesel after it was shut off? they said hmmmmmmm. What kind of fuel due ya burn? 91 octane I said. How about the valve stems they may be worn and causing the appearance of a vacuum leak. I said wouldn't it burn oil and foul plugs?

So I guess my question is would a bad ECM cause this type of problem? Its the original 1226026 with the TCC fixed eprom. My thinking is that it has to be something simple, but I sure as sh.. (or the dealter for that matter) can't find it. What am I missing???

 

[elkabong]

JoBy - Well after all the pain and what not it turns out your are correct. I humbly bow to your wisdom and knowledge.

elkabong

 

[geekinavette]

So Jim, you found that the balancer had in fact slipped?

Are you still getting the code 42?

 

[elkabong]

I have not checked yet. They also replaced the ignition module so the original code was lost. They said it was flakey and replaced it. I will check this weekend. It was an intersting process. The tech flailed around for two days until I was able to speak with him directly. I told him what to look for-the comment was made that nobody knows how to work on crossfire any more. The last item was the balancer which was the problem.

I still have the slight surge at idle. I am thinking the TBs need to be adjusted and that will be my next adventure. Hopefully, I will get to port my new manifold and have the TBs bored to 2 inches which will meet my long term goal. So the TB work I will be doing shortly is considered as 'training' for the real deal.

 

[geekinavette]

Cool, well glad to hear you finally tracked this problem down. Those darn balancers have caused many 'o nightmare.

Definately get those TBs balanced...that will cause major problems if they're not.

Bill

 

[elkabong]

I have been reading the stuff on CFI for the TBs. I have also posted some questions CFI which have probably been answered.

 

[oldace84]

Yep check your timeing...what octane gas are you using?????
Did you buy gas after a rain.....never do this......
check it out...
Hope I have helped a little bit...
tony

 

[elkabong]

As it turned out it was the harmonic balancer. Apparently the original is a bad design and in some cases the outer ring (where the timing marks are) will slip. I replaced the balancer and life is good once again.

 

[Moonunit 451]

Did you buy gas after a rain.....never do this......

oldace84, enlighten me. I've never heard this. This would be difficult to do living in Oregon:eek