1st TBI Conversion Help Needed

[4WDKC]

what is the gap on the plugs, what coil are you using?

 

[MtBraun]

to be honest I only checked the first one out of the box, it was .035. Stock coil from 91 donor truck.

 

[1987 GMC Jimmy]

I've had the contact on the plug side of a single wire get cooked before so maybe check for that and even the whole wire. They can degrade internally over time, and on the off chance it's arcing, that could cause a black plug, too.

 

[MtBraun]

I've had the contact on the plug side of a single wire get cooked before so maybe check for that and even the whole wire. They can degrade internally over time, and on the off chance it's arcing, that could cause a black plug, too.

They are original wires so that is a good thought. Does a guy need to go to the larger 8mm wires or are stock replacements sufficient for this application?

 

[4WDKC]

They are original wires so that is a good thought. Does a guy need to go to the larger 8mm wires or are stock replacements sufficient for this application?

I always go with the bigger wire as I cant see it hurting other than wallet, get a coil for a 96+ vortec truck they have more voltage and can jump larger gaps where as the tbi cannot and your stock one from the donor is probably very low on voltage.

 

[1987 GMC Jimmy]

On the flip side, I just have the Delco standard replacement wires and a stock coil, and I’m running well. I may upgrade in the future, though.

 

[MtBraun]

I replaced the spark plug wires and still have the same symptoms, albeit slightly better than originally. It doesn't seem to cut out as bad after fully warmed up. I'm really beginning to question my thought process for using all u-pull parts for this conversion.

So do you think the next item to address is the coil? Is there any way to test the coil? I hate just throwing parts at this problem.

 

[1987 GMC Jimmy]

I do have a troubleshooting diagram for you to look at. You could also try getting a test light and hovering the tip over the high energy connector to see if you get a bright white spark and not a dull yellow one while you crank it. That's really all the coil does, though. If you try the latter, it'd be a good idea to unplug the injectors so you don't flood the engine. I don't think it's that, but you can't be 100% till you try.

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[MtBraun]

Thanks for sharing the diagram. The coil tested fine per that diagram. I did not try to arc the coil to a test light yet. The weird thing is that the symptoms seem to get much better once the truck is fully warmed up. No codes so I'm flying blind a bit.

My neighbor mechanic set the timing, I'm assuming to 0 before connecting the EST bypass. I've read some other posts suggesting the TBI motor liked 2 degrees advanced instead of 0 at base timing.

Since my symptoms are better when warm I'm not sure its timing related.

 

[1987 GMC Jimmy]

Thanks for sharing the diagram. The coil tested fine per that diagram. I did not try to arc the coil to a test light yet. The weird thing is that the symptoms seem to get much better once the truck is fully warmed up. No codes so I'm flying blind a bit.

My neighbor mechanic set the timing, I'm assuming to 0 before connecting the EST bypass. I've read some other posts suggesting the TBI motor liked 2 degrees advanced instead of 0 at base timing.

Since my symptoms are better when warm I'm not sure its timing related.

That timing is not gonna make it have or not have those issues. More advanced timing will make for a more efficient power stroke, burn less fuel, run a little leaner, and make it have a little more pep. You can advance it up to 10* if it doesn't ping, but mine's actually in the same place yours is. Is your coolant temperature sensor used or new? If it's used, I'd get a new one no questions asked. Those things will degrade without showing a code, but I don't want you to throw parts at it because of what I said. Have you gotten your hands on something to look at the sensor data with yet?

 

[MtBraun]

Funny, I was thinking about the coolant temp sensor on my way to work this morning. The current sensor is from the donor truck. Since we've been getting some snow up here it's been put to work a fair amount and haven't had time to get the cable and tuner pro setup done. I was hoping I could just get this thing running well and not have to jack with data logging. I'm so close!

I'm going to pick up a coolant temp sensor and see if that helps.

 

[MtBraun]

Well I put on a new coolant temp sensor and that did not help. Downloaded Tuner Pro RT and need to get a cable ordered. The symptoms aren't bad enough to prevent us from using it but are annoying enough to want to fix.

 

[1987 GMC Jimmy]

Well I put on a new coolant temp sensor and that did not help. Downloaded Tuner Pro RT and need to get a cable ordered. The symptoms aren't bad enough to prevent us from using it but are annoying enough to want to fix.

Sorry to hear that. I hope you can find something when you get the computer hooked up to it. That way you can see things right away that the computer would otherwise wait to tell you about or may miss. Can you give a recap of what you've done so far?

 

[MtBraun]

I plowed some snow with it this morning and got a better feel for the symptoms. When cold, it has a really bad dead spot right off idle. It will pop and die sometimes. If I feather my way through the throttle I can keep it running. If I mash it to the floor from idle it goes right through the dead spot. When fully warmed up, it is a little saggy off idle but the dead spot isn't nearly as bad. It starts and idles fine.

So far this is what I've done.

AFI harness
New ECM with Dave W tuned chip (based on AMUR bin)
No EGR or knock (also tuned out in chip)
New oxygen sensor
New TPS
New coolant temp sensor
New spark plug wires, cap, and rotor

No codes, injectors appear to be spraying a nice uniform pattern. Fuel pressure tested at filter was 13 PSI with key on and engine running.

 

[MrMarty51]

Almost sounds like a timing issue.
Is the brown or tan with the black stripe hooked into the system ?