TBI hesitation and backfire

[clstolten]

I am trying to make GM TBI work on a non tbi motor. The motor is very mild with an RV cam, and edelbrock performer manifold. Just recently fired it for the first time since a full rebuild. The tbi system was taken from an 88 K5 with a 350 and 700R4. The chip is from a 89 truck that had a sm465, since my truck has an sm465. The problem I am having is that I will get a hesitation and backfire through the intake under load or heavy acceleration. Also it backfires through the exhaust when I let off the gas. Here is what I have checked or replaced in my attempts to fix this problem: Checked compression and have 125 to 135. Vacuum at idle is a rock solid 14 inches, which I think is ok since I live at 6700 feet elevation. I have checked valve adjustment. Replaced and properly gapped plugs. Replaced wires. Replaced ignition coil and module. Anybody have any suggestions on what to look for? I had a very similar problem with my 95 LT1 Impala when the MAF got dirty. I am thinking this is fuel related, and I am running lean.

 

[southernspeed]

Sounds like a lean condition. I'm not so sure a stock chip will handle that motor too well. Have you run winaldl to see how it's fueling? Is you timing set to zero?

 

[Big91RustyBucket]

Timing set to zero is important as the computer is going to adjust that. It kinda sound's like a cam that maybe should not be in there. Some cam's you need to run a FI setup that you can really tune . Because it isn't a computer controlled cam the computer doesn't know what to do. Good luck and let us know how it goe's.

 

[clstolten]

The timing is set to zero. I have winaldl, and cable but need to get a power source for my laptop since the battery is shot. I am going to borrow a friends wideband 02 and display to verify the lean condition. Any chance this could be TPS related? I have monitered TPS voltage with winaldl and it looks good, but the refresh rate is weak and might not show a problem. I will try and check it with my voltmeter later today.

 

[BLZN4FN]

You may want to contact B_to_C I know when he did his swap he was having some problems kinda like yours he maybe able to help you out.

On a side note that th350 I got from you about 3 years ago do you remember if it needed to be rebuilt or it was a good tranny?

 

[clstolten]

I will PM B_To_C and see what he thinks.

The TH350 should be good internally. It made the drive from Palmdale CA to Denver no problem and shifted great. I do remember that one of the mounting holes on the case to the engine was kinda messed up. Otherwise just run it.

 

[JEBSR]

Low fuel pressure could cause similiar symptoms as well.

 

[B_to_C]

Sorry Craig, the best advice I can give you is to get some good ALDL data to analyze. It is posible that with your non-stock cam you may need to get a custom chip burned for your truck to run correctly.

When I was having these problems it was because I was using a chip for an auto transmission blazer...once I swapped in a stock chip for a manual equipped truck these problems went away (not that my truck is problem free )

I got my chip from TBICHIPS.com The guy was extremely knowledgable and I wouldn't hesitate to suggest him to anyone.