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Old 01-25-2009, 04:49 PM
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TBI conversion problems

Hi everybody. I am new to the posts here and need some desperate help. I have done a TBI conversion on my 1976 Chevy C10. I got it started but it runs HORRIBLE. I have to babysit the idle until it is warmed up. The idle fluctuates from low to high and often dies. During the first few times of starting it, it dies immediately. I have checked everything imaginable. The IAC and TPS have been adjusted and seemed to help for a day or two but then quit. The egr has been disconnected to rule it out as a problem. The fuel pressure is steady at 12PSI. It has a new cap, rotor, plugs, and wires. There are also a few other problems. It was going into closed loop until I cut the oxygen sensor wire close to the firewall and ran it straight to the O2. The wire had several kinks and bends that were pretty bad. The other problem is an occasional popping in the exhaust and an intake backfire. i hooked it up to the snapon scanner tonight and here are some of the results:

Closed loop: no TPS voltage (idle): .66V Throttle % : 4% (never changed even when revving) IAC position: 70-80 desired idle: 1600!!
Block Learn: 128 Coolant temp: 89C
MAP Kpa: 35-36 MAP voltage (idle):1.3-1.5
ESC count:0 knock: no
IAC position (listed twice for some reason): 69-75

I have to admit, this has been driving me crazy for quite some time. Another thing I thought I noticed is the scanner said something about running in limp mode? I have no idea what would cause this. Any help would be greatly appreciated.

Edit: Figured out the no closed loop problem. There was an intermittent problem with the oxygen sensor wire after I cut it shorter.

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Old 01-25-2009, 05:15 PM
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Your TPS reading of no volts at idle, and the fact that it does not change to wide open throttle is a major concern. It is either defective, or installed wrong. You could also have the idle stop screw, turned in too far.

What did the throttle body come off of? Might be a different CFM rating than you need.

Things to check;

The injectors pulse width.
Pull the EGR valve, and check for by-passing.
Make sure the throttle is going completely closed.
Make sure you have manifold vacuum to the MAP sensor, and it holds vacuum.


Post the ECU part Numbers, and remove the cover over the Prom, and post those #'s also. You just might have a ECU, and Prom from a M4ME carb. set up. Could you also post the scan tools Prom ID number?

Last edited by carsavvycook; 01-25-2009 at 06:01 PM. Reason: addition
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Old 01-25-2009, 05:48 PM
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Are you retrofitting the TBI onto an older engine, or did you swap the whole engine? If you swapped the whole engine, then we're on the right track toward diagnosis. If you just put the TBI on a different engine you can't expect it to run right. The TBI computer is not very intuitive or adaptable. The fact that the older engine has different cam, compression, head flows, vacuum signals, exhuast, intake, etc means that it won't know how to adjust the fuel map to give proper operation. A new PROM will have to be burned for it.
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Old 01-25-2009, 05:59 PM
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Quote:
Originally Posted by curtis73
Are you retrofitting the TBI onto an older engine, or did you swap the whole engine? If you swapped the whole engine, then we're on the right track toward diagnosis. If you just put the TBI on a different engine you can't expect it to run right. The TBI computer is not very intuitive or adaptable. The fact that the older engine has different cam, compression, head flows, vacuum signals, exhuast, intake, etc means that it won't know how to adjust the fuel map to give proper operation. A new PROM will have to be burned for it.
You are on the same wave link, as I am, on this thread.

This is why I requested ECU, and Prom numbers.
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Old 01-25-2009, 06:44 PM
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The tbi has been swapped onto a carb engine. I am not aware of the scan tools prom id. It is up at our college since that is where I currently have the truck. The engine is a rebuilt one from autozone and has the exact same cam specs as the tbi cam according to the research I have done. Compression is a bit lower, it is running about 8.3:1. The ecm is a 1227747 with the ACSU prom. From the research I did, this is the most "adaptable" ecm for conversions like mine. My engine is a 350 and the ecm came from a 1990 c1500 with a 350 and 500CFM throttle body. I am concerned about the tps also. The only thing i forgot to mention is the tps % never changed but the voltage did go up to about 5 volts at wot. I have tried tampering with the idle stop screw before and messed things up. I intend on switching another throttle body on that the idle screw cant be adjusted.There is for sure vacuum at the MAP but I will have to get a hold of a hand held vacuum pump to see if it holds vacuum. I have disconnected the EGR to see if that eliminated the problem but no change.
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Old 01-25-2009, 07:47 PM
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Have you switched the wire loom, or are still using the original wire loom in the truck?
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Old 01-25-2009, 09:06 PM
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Not too sure what you mean by changine the wire loom in the truck. However, i can say that I just used the stock harness from the donor vehicle and added it into the engine bay plus kept my stock harness seperately. Hope this is what you were asking for.
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Old 01-25-2009, 09:30 PM
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That is what I was asking for, now do you have the correct coolant temp sender for the computer installed, and hooked up?
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Old 01-25-2009, 09:52 PM
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I have everything hooked up that a 92 c1500 has hooked up. I have even went as far as installing a VSS and P/N indicator switch.
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Old 01-25-2009, 09:57 PM
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I would still need that scan tool Prom ID Number, along with all of the lettering and numbers on it.

Thank you for giving accurate information.

Last edited by carsavvycook; 01-25-2009 at 09:58 PM. Reason: spelling
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Old 01-25-2009, 10:03 PM
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I'll bet that donor truck is feeling a little bit violated at this point.

Did you hook up all of the ground wires from the donor harness, with good clean connections?
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Old 01-25-2009, 10:13 PM
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I do indeed have all of the grounds hooked up to good clean connections. I do not know how or where I would find the prom id on the scanner. I can tell you this. It is a genisys scanner running the 3.0 version. Here is a link if that will help.

http://images.google.com/imgres?imgu...3Doff%26sa%3DN
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Old 01-25-2009, 10:41 PM
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Quote:
Originally Posted by chevy_c10
I do indeed have all of the grounds hooked up to good clean connections. I do not know how or where I would find the prom id on the scanner. I can tell you this. It is a genisys scanner running the 3.0 version. Here is a link if that will help.

http://images.google.com/imgres?imgu...3Doff%26sa%3DN
The Prom ID information should show up in the current vehicle serial data program.

When you remove the ECU, and remove the cover from the back side, for the Prom(it's just 2 screws) you will see the ID numbers on the Prom. These numbers are different than the scan tool ID numbers. I will need all 3 to find out if you are having a conflict, or if there is an up-dated Prom available.

As suggested, you may need to order a after-market Prom for it.

We won't know until you can supply us with these numbers.

Last edited by carsavvycook; 01-25-2009 at 10:44 PM. Reason: wrong wording
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Old 01-25-2009, 10:56 PM
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All right, tomorrow i will get the ecu part numer, ecu prom id number, and the prom id number of the scanner. I will post back in the evening. Thank you so much for the help so far.
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Old 01-25-2009, 11:04 PM
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I'm just trying to be of some help. What time are you planning on posting tomorrow?

Remember I am a little bit farther West from you. LOL
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