Tbi 350 has no power on the road

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kylenautique

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I haven't read through all the pages, so I'm sorry if you have tried all of these things.. I would recommend replacing the ignition module with an AC Delco brand. I had a TBI system that was converted to run MPFI for a TPI system. I always had issues with the ignition modules failing. I've also had other friends with the same issue. I would install a new one, and personally, I would install an AC Delco brand distributor with it. That solved my issues. When the ignition modules fail, they can make for rough starting..no starting and a serious lack of power. I would also check your injectors to make sure they are spraying fuel properly. Just shine a timing light on them. Make sure your advance is working. In base timing, it will kill the advance by disconnecting the wire by the distribtor. When connected, if you look for the timing mark with a timing light, it should bounce all over the place. If its not, that brings you back to the distributor. Last thing... The ECM could be the issue. They are usualy pretty rock solid, but sometimes they can develop a hickup. Since you don't have a 4l60e, you could upgrade to the Dynamic EFI computer which is sooooooo much better than the stock ECM you are running. https://www.dynamicefi.com/

Last option... Ditch the system and throw a Holley Sniper on it :)

Good Luck man, OBD1 is so simple, but it can be a serious pain in the a$$ sometimes.
 

L31MaxExpress

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I haven't read through all the pages, so I'm sorry if you have tried all of these things.. I would recommend replacing the ignition module with an AC Delco brand. I had a TBI system that was converted to run MPFI for a TPI system. I always had issues with the ignition modules failing. I've also had other friends with the same issue. I would install a new one, and personally, I would install an AC Delco brand distributor with it. That solved my issues. When the ignition modules fail, they can make for rough starting..no starting and a serious lack of power. I would also check your injectors to make sure they are spraying fuel properly. Just shine a timing light on them. Make sure your advance is working. In base timing, it will kill the advance by disconnecting the wire by the distribtor. When connected, if you look for the timing mark with a timing light, it should bounce all over the place. If its not, that brings you back to the distributor. Last thing... The ECM could be the issue. They are usualy pretty rock solid, but sometimes they can develop a hickup. Since you don't have a 4l60e, you could upgrade to the Dynamic EFI computer which is sooooooo much better than the stock ECM you are running. https://www.dynamicefi.com/

Last option... Ditch the system and throw a Holley Sniper on it :)

Good Luck man, OBD1 is so simple, but it can be a serious pain in the a$$ sometimes.

I have had decent luck with AC Delco years ago, then those started giving me issues similar to aftermarket. When that happened I was grabbing junkyard actual OE modules, had better luck with them than the new ones. Then I found Davis Unified. Been running Davis Unified modules and coils the last 15 years in everything TBI, TPI, LT1 or Vortec I have owned or built save for the newest build 87 G20 with its highly specific list of coils compatible with the Proflow 4 system. Maybe the GM ones have improved but back around 2007 or 2008 the quality of them nose dived and I was fighting issues even including DOA modules and coils.
 

L31MaxExpress

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I haven't read through all the pages, so I'm sorry if you have tried all of these things.. I would recommend replacing the ignition module with an AC Delco brand. I had a TBI system that was converted to run MPFI for a TPI system. I always had issues with the ignition modules failing. I've also had other friends with the same issue. I would install a new one, and personally, I would install an AC Delco brand distributor with it. That solved my issues. When the ignition modules fail, they can make for rough starting..no starting and a serious lack of power. I would also check your injectors to make sure they are spraying fuel properly. Just shine a timing light on them. Make sure your advance is working. In base timing, it will kill the advance by disconnecting the wire by the distribtor. When connected, if you look for the timing mark with a timing light, it should bounce all over the place. If its not, that brings you back to the distributor. Last thing... The ECM could be the issue. They are usualy pretty rock solid, but sometimes they can develop a hickup. Since you don't have a 4l60e, you could upgrade to the Dynamic EFI computer which is sooooooo much better than the stock ECM you are running. https://www.dynamicefi.com/

Last option... Ditch the system and throw a Holley Sniper on it :)

Good Luck man, OBD1 is so simple, but it can be a serious pain in the a$$ sometimes.

Just noticed you mentioned an EBL because it was not a 4L60E, the OP does have a computerized transmission. He has a 4L80E, 1991 was the first year for that.
 

tayto

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I agree. Just because the parts cannon has been unloaded at this thing multiple times does not mean those parts can be crossed off the list! I have been through this twice on 2 different trucks that were not mine since COVID.

1st was a GMT400, we were trying to get the thing reliable for a friend of mine that does landscaping. Figured we'd put a new reman distributor for piece of mind. of course, the old one got removed and returned before the new one was put in. Ran like crap no matter what I did. Sent back to rockauto and ordered another one. after going through this two more times, I finally gave up and rebuilt a factory distributor. problem solved.

2nd was early 80s square body dump truck. Weak spark. gave buddy a parts list to rebuild and he goes and buys a brand new Accell. Starts eating coils and modules. So what does he do? Buys another Accell. Does same thing and then he starts swapping parts out from the other accell distributor. I finally said enough and threw in my GM performance distributor that was in my truck, been over a year now and no issues.
 

Mitchell93

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OK, so my distributor is on correctly, looks just like that picture that L31MaxExpress posted, I got a CHEEP dial indicator from harbor freight, it's junk, it takes so long to set up, I did the entire left bank, and really don't want to do the right, it's just so frustrating setting it up, and I feel confident in the numbers I already have, I I believe my problem is a severely warn camshaft, here are my lobe lifts:
Cylinder 1:
Exhaust 0.260
Intake 0.241
Cylinder 3:
Intake 0.249
Exhaust 0.249
Cylinder 5:
Exhaust 0.248
Intake 0.223
Cylinder 7:
Intake 0.239
Exhaust 0.248
This is lobe lift not valve lift

Now alldata tells me my spec. is:
Intake 0.2565. +or- 0.002
Exhaust 0.2690. +or- 0.002

Also, before anyone asks, yes I removed the rockers so I don't compres the lifters... I've checked each one as many time as it took to get the same value 3 times I tried a acdelco ignition module already. I believe it's my cam now, what do you guys think? I'm sure this spec. Is a rebuild spec, I'm not sure how far from spec it can be before it has issues...
 

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Schurkey

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Based on your description from the first post, and the fact that you removed the rockers leading to difficulty in keeping the pushrods straight--and the resulting measurement error--I have little enthusiasm that the cam wear as indicated by your measurements has anything to do with the engine performance.
 

Mitchell93

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Based on your description from the first post, and the fact that you removed the rockers leading to difficulty in keeping the pushrods straight--and the resulting measurement error--I have little enthusiasm that the cam wear as indicated by your measurements has anything to do with the engine performance.
Part of the reason I was so frustrated with it was because I measured them all with the rockers on, and they kept bleeding down, so not one I was confident with, so I took them off, and now I'm confident. The worst part was setting up the cheep Harbor freight tool, keeping the pushrods straight is the easy part...
 

tayto

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get an extension for your dial indicator so you can take the reading off the lifter. trying to get an accurate reading off of an unsupported push rod is going to be a guessing game. honestly, running the engine with the valve covers off and eyeballing the rockers probably would have sufficed here..... 0.020" (.030 at the valve) difference ain't **** on high mileage stock engine.
 
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