Vince's TBI woes, progressive revelations, and tbi mods.

[Vbb199]

Alrighty gents, i stabbed the dizzy in 180° out from where i had it, unplugged the est bypass, and it fired right up

Not even a 1 second crank and it fired off. Set the timing, locked it down, killed the battery, plugged the bypass back in...

Now later i'll see if the stumble/misfire is gone

 

[Vbb199]

I should say it was running and driving in the yard and idling, so thats already a good sign

 

[Catbox]

Gently....

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[Vbb199]

Gently....

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I like the added "gently" detail haha

 

[Vbb199]

Back again!
That didnt fix jack ****

 

[Vbb199]

I guess before i take my intake off, im going to swap my ICM out, as a final ditch effort

Everyone including me believes if thats bad, it just dies, but some reading on the gmt400 forums seems to suggest otherwise.

Im seeing the tach bouncing and spiking around, and its in sequence with the misfiring and bad behaviour.

 

[AuroraGirl]

Update 69.2:
That did nothing in terms of the weird idle jumping around lol

I then proceeded to spray carb cleaner around the blocked off egr, tbi, intake and vacuum lines and saw no change.

So whats next

the screens are for production purposes in case anything upstream was introduced unintentionally and can be discarded but dont hurt nothing

also, dont know if you are having IAC issues still but
If you turn the key ON, then ground the A-B connectors of the ALDL under the dash, the ecm will drive the IAC valve all the way closed. This is ZERO "counts". The engine should be able to RUN in this condition albeit possibly lopey and may take a couple tries to start if its cold.

you can also peform a throttle snap test to determine if its over or under traveling, in that it would deliver inconsistent results and behavior that may not be apparent when viewing the live data in a given situation

THe throtle counts , to me, seem high but not too high.
basically while viewing the data at a stable idle, fully blip the throttle like 7 times quickly and quick release, then when done your final value should be within 5 counts of the beginning

If its beyond or below that, your IAC is not responsive enough or its mechanically wearing and its unable to know that itself

 

[AuroraGirl]

I guess before i take my intake off, im going to swap my ICM out, as a final ditch effort

Everyone including me believes if thats bad, it just dies, but some reading on the gmt400 forums seems to suggest otherwise.

Im seeing the tach bouncing and spiking around, and its in sequence with the misfiring and bad behaviour.

Your tach is jumping around? timing light time. sounds like it could be a weak pole piece in the distributor. when you have the distributor out, rotating the shaft can you feel the magnetic poles as you rotate? the magnetic feel will resist turning and it should happen when they get aligned (so twice in a 360 rotation i think? maybe once idk)

There is a way to see this on a timing light if you want to see the procedure i can show you a video

 

[bucket]

@Vbb199

I thought I mentioned the ignition module as being a possibility. They usually work or not, but on occasion, they do act just kinda goofy instead of dying completely.

 

[bucket]

Your tach is jumping around? timing light time. sounds like it could be a weak pole piece in the distributor. when you have the distributor out, rotating the shaft can you feel the magnetic poles as you rotate? the magnetic feel will resist turning and it should happen when they get aligned (so twice in a 360 rotation i think? maybe once idk)

There is a way to see this on a timing light if you want to see the procedure i can show you a video

You should feel the magnetic effects every 8th of a turn. The inner and outer rings have 8 points each, for an 8 cyl engine.

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^^^And as crappy as that one looks, it still works perfectly fine.

 

[AuroraGirl]

You should feel the magnetic effects every 8th of a turn. The inner and outer rings have 8 points each, for an 8 cyl engine.

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^^^And as crappy as that one looks, it still works perfectly fine.

dear lord nitric acid damage

 

[Vbb199]

@Vbb199

I thought I mentioned the ignition module as being a possibility. They usually work or not, but on occasion, they do act just kinda goofy instead of dying completely.

Its what im gonna try next. Thats for sure, thats not the OEM one, but aftermarket that came with the distributor i put in a couple years ago. My old dizzy was sloppy as all get out with 300k+ miles on it lol

I recall like.... 2 years ago... I put the accel dizzy in with some sort of jacobs ignition. I was always seeing the needle jump a little here and there on my tach afterwards.

iTs never stopped doing it but its never caused issues like ive been experiencing. I assumed it to be EMI or something.

2 months ago when this started it was an intermittent misfire , now its just plain running like ass

Yesterday when i went to drive it, intially it was ok, like within the first 5 minutes of driving and idling, it was running up and over 3000, no misfiring etc.
Then it just started to break up and fall apart, the needle was jumping around like crazy, it stalled on me twice in the road, it was hiccuping and bucking here and there

You'd think if it was a vacuum leak it would act up immediately,
Seems to me like the ICM must be getting warmed up and then malfunctioning.

Im gonna change it today on lunch and see what that does. I got two stock OEM ones i keep in the truck, including the original one to the truck

 

[AuroraGirl]

Its what im gonna try next. Thats for sure, thats not the OEM one, but aftermarket that came with the distributor i put in a couple years ago. My old dizzy was sloppy as all get out with 300k+ miles on it lol

I recall like.... 2 years ago... I put the accel dizzy in with some sort of jacobs ignition. I was always seeing the needle jump a little here and there on my tach afterwards.

iTs never stopped doing it but its never caused issues like ive been experiencing. I assumed it to be EMI or something.

2 months ago when this started it was an intermittent misfire , now its just plain running like ass

Yesterday when i went to drive it, intially it was ok, like within the first 5 minutes of driving and idling, it was running up and over 3000, no misfiring etc.
Then it just started to break up and fall apart, the needle was jumping around like crazy, it stalled on me twice in the road, it was hiccuping and bucking here and there

You'd think if it was a vacuum leak it would act up immediately,
Seems to me like the ICM must be getting warmed up and then malfunctioning.

Im gonna change it today on lunch and see what that does. I got two stock OEM ones i keep in the truck, including the original one to the truck

read what i wrote above about the distributor magnets and using a timing light , it might show you saomething about your issue. also read about the IAC counts.

 

[gmbellew]

Its what im gonna try next. Thats for sure, thats not the OEM one, but aftermarket that came with the distributor i put in a couple years ago. My old dizzy was sloppy as all get out with 300k+ miles on it lol

I recall like.... 2 years ago... I put the accel dizzy in with some sort of jacobs ignition. I was always seeing the needle jump a little here and there on my tach afterwards.

iTs never stopped doing it but its never caused issues like ive been experiencing. I assumed it to be EMI or something.

2 months ago when this started it was an intermittent misfire , now its just plain running like ass

Yesterday when i went to drive it, intially it was ok, like within the first 5 minutes of driving and idling, it was running up and over 3000, no misfiring etc.
Then it just started to break up and fall apart, the needle was jumping around like crazy, it stalled on me twice in the road, it was hiccuping and bucking here and there

You'd think if it was a vacuum leak it would act up immediately,
Seems to me like the ICM must be getting warmed up and then malfunctioning.

Im gonna change it today on lunch and see what that does. I got two stock OEM ones i keep in the truck, including the original one to the truck

Definitely something heat related, it seems. ICM is an easy swap to check. if the ICM doesnt fix it, you might scan from a cold start and see if the issue just happens to coincide with going into closed loop just to be sure it isnt something sensor related? could be multiple issues also....something weird in ignition causing the tach bounce and a separate issue causing the drivability problems. these kind of issues drive a person nuts. I hope you get it figured out!

 

[Vbb199]

Swapped the icm out with the oem one from 1989 and shes purring good now as im typing this. No jumpy tach and the idle isnt jumping around and doing weird shyt
I havent got the time to drive it, but i'll report back later.

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