SBC 383 TBI Problems (1 Viewer)

[Roger]

FJ60,86 SBC 383 TBI /700R4

This conversions runs great for short distances, less than an 1hrs constant driving. Everytime that a long drive is made and after about 2hrs at hiway speed (70-75mph) the engine develops a miss and runs poorly. I've taken it back to the mechanic who built up the 383 and he has replaced sparkplugs and wires. Everything runs great until again I take it on a longer trip at hiway speeds and the same thing repeats itself. This last time the wires were again replaced and the #8 plugs electrode was bent in touching the firing tip of the plug. This work was not done by the original mechanic but in an out of state garage the engine was running so ruff I was afarid to crippel it home. This mechanic suggest he tought that the engine was running to lean and that the computer needed a new chip or the chip modified to properly work with the change from 350 TBI to 383 TBI. My question is, is the 2nd opinion going in the right direction? This repeating condition needs to be fixed and am looking for the right solutions. I hope there is sufficient info here for some of you with experience with this conversion to help me help my mechanics. Roger

 

[alaska60]

FJ60,86 SBC 383 TBI /700R4

This conversions runs great for short distances, less than an 1hrs constant driving. Everytime that a long drive is made and after about 2hrs at hiway speed (70-75mph) the engine develops a miss and runs poorly. I've taken it back to the mechanic who built up the 383 and he has replaced sparkplugs and wires. Everything runs great until again I take it on a longer trip at hiway speeds and the same thing repeats itself. This last time the wires were again replaced and the #8 plugs electrode was bent in touching the firing tip of the plug. This work was not done by the original mechanic but in an out of state garage the engine was running so ruff I was afarid to crippel it home. This mechanic suggest he tought that the engine was running to lean and that the computer needed a new chip or the chip modified to properly work with the change from 350 TBI to 383 TBI. My question is, is the 2nd opinion going in the right direction? This repeating condition needs to be fixed and am looking for the right solutions. I hope there is sufficient info here for some of you with experience with this conversion to help me help my mechanics. Roger

You need LEHIGUY's input......he plays with these TBI's quite often....almost enough to call it abuse.
Im sure when he sees this thread he will chime in!

 

[brokenparts]

I'd tend to agree that it is running lean. The ecm is probably going into "lean highway cruise" which leans out the fuel ratio when a certain speed and temp thresh hold is achieved. It can be deleted out or properly tuned with a custom burned chip. You can buy the gear to do so or you can go through someone like TBIchips.com to burn one for you. I have nothing but good things about tbichips.com. Having a chip burned for you will probably improve you mpgs and power too.

 

[lehiguy]

Your bent electrode was almost certainly the result of some pretty bad detonation from a lean condition. From your description of the problem and its delayed onset, I would suspect fuel supply issues, possibly from a gas tank venting problem. Are you finding a vacuum when you take off the gas cap when this happens? Is the EGR on your system disabled or is it still present? What fuel pump are you running and at what pressure? As has been mentioned, Brian at tbichips.com is terrific to work with and can delete unwanted things like EGR or VSS from your chip if needed. In the mean time, start looking over your fuel supply system including the evaporative emissions and tank venting (the obvious stuff like filters goes without saying). I bet you will find your problem.

 

[alaska60]

Your bent electrode was almost certainly the result of some pretty bad detonation from a lean condition. From your description of the problem and its delayed onset, I would suspect fuel supply issues, possibly from a gas tank venting problem. Are you finding a vacuum when you take off the gas cap when this happens? Is the EGR on your system disabled or is it still present? What fuel pump are you running and at what pressure? As has been mentioned, Brian at tbichips.com is terrific to work with and can delete unwanted things like EGR or VSS from your chip if needed. In the mean time, start looking over your fuel supply system including the evaporative emissions and tank venting (the obvious stuff like filters goes without saying). I bet you will find your problem.

I knew you wouldnt be able to hold back much longer..............

 

[lehiguy]

I knew you wouldnt be able to hold back much longer..............

Its a lifetime affliction.

 

[ntsqd]

And the rest of us benefit from it, for which I am glad.

 

[Roger]

First let me thank all of you. I am a gun mechanic not a engine mechanic and I know just enough to get in serious trouble. I have forgotten to add a detail that may confirm and/or add to my troubles.

Original conversion to 350TBI has 2 fuel pumps(1-hi-pressure and 1 low pressure matched to what the factory setting are for 350TBI) with a small reservoir/return from TB and 2 filters, all new hoses from gas tank to this set up and to TB. This had worked great for 6 years. I did not then nor do I know recognize a vaccum when I open the gas cap in fact the opposite when it is hot weater and my tank is near empty.

The part I did not include with my original post is that this 383TBI set up I have notice that the idle is perfect 6-800RPM in the short run situations and in the long run situation and after 1+hrs the idle changes to 12-1400RPMs. When engine cools after a long run my idle return to normal. This sometimes is an indication of a vaccum problem and may as some have suggested one in this application.

Again please accept my heart felt thanks for your guidance. I dearly love my FJ60. Roger

 

[lehiguy]

How much gas tank pressure? Do you have a charcoal canister in the plumbing? Your idle is going up, most likely, because of the very lean condition that exists at that time, your exhaust gases would be off the charts for NOX. Explain this resevoir you mentioned. Is that on the return line?