Expert TBI Assistance Needed

[bkshir]

I also looked into the issue with it always showing to be in Park. There was a wire connected at Pin B10 in my Howell harness that was providing ground at all times. I didn't trace it down, but I did remove the pin from the connector and tape it up and zip tie it along side the harness. I was running low on gas and time, so I took a short test run around in the field near my house. It immediately started idling lower. I lugged it down to the point that the IAC was running pretty much wide open and then pushed in the clutch. The RPMs flared up as you would expect, but then it settled back into an idle around 750-800 RPM. That is when it would have normally continued to rev around 1750-1800 RPM. So, that seems to have made a huge improvement. Thanks Bill!!! I will have to test drive it some more when I have time, but it is definitely getting better. I have attached a short LOG file of my test run. Thanks again for your help.

Bill

[Bill usn-1]

Good progress.

[Bill usn-1]

You need to back the min idle screw out about 1/2 turn.

[bkshir]

OK. I will do that next. I have a question for you. Will the B10 Park/Neutral being grounded affect the way the engine performs under a load? It was cutting out when trying to accelerate when it was cold and would hesitate when I jumped on the gas even when it was warmed up. I will have to test drive it some more, but was just wondering if I should expect improvement in those areas as a result of the fixes I have done or not. Thanks again for your help.

Bill

[Bill usn-1]

I don't run them after I find the problem so I couldn't really say what all it would affect.
Obviously it changed how it idles so it affects the IAC position.

You will tell when you drive it.

[EagleMark]

Originally Posted by bkshir

OK. I will do that next. I have a question for you. Will the B10 Park/Neutral being grounded affect the way the engine performs under a load? It was cutting out when trying to accelerate when it was cold and would hesitate when I jumped on the gas even when it was warmed up. I will have to test drive it some more, but was just wondering if I should expect improvement in those areas as a result of the fixes I have done or not. Thanks again for your help.

Bill

Since you already have seen a differance (baseline) let us know.

I purposly disconected one once on a chevy that came with the TBI type system we play with here and only thing I noticed was harder bang when putting the Suburban in gear, mostly cold.

[bkshir]

OK. I drove the Jeep around some this morning when it was nice and cold (around 30F) to see if there was any change in performance when the engine was cold. Here are the results.

When the engine is cold, it still acts up pretty badly under mild to moderate loads. I don't know how to describe it other than to say it shudders (similar to how a V8 would with about 3 or 4 cylinders not firing). If I really get on it, it will cut out some and then kick in and run like hell once I get near WOT.

Disconnecting the wire at Pin B10 (Park/Neutral) seems to have solved all of the idle problems I was having. When the engine is at operating temperature, it would nearly pass for running completely normal. Sometimes, it almost feels like a very slight hesitation when I transition from just maintaining speed to a slight acceleration. And, if I go WOT very quickly when driving at low RPMs it will bog a little. In hopes that this information may help someone else sometime, I wanted to mention that disconnecting the Park reference wire did not seem to affect engine performance under load in any way.

I did adjust the base idle to bring up the IAC count and then readjusted the TPS to bring it back in spec when I got home tonight. The attached LOG files are from after those adjustments. The engine was warmed up by then so, it was running pretty well during that run.

So, overall I am quite happy with the way it performs except when it is cold. Could running a 4BBL intake with adapter plate cause issues like this? I have heard that TBI systems run best with an original TBI intake. The strange thing is that it ran similarly when cold when I had the carb on it, but I always just attributed it to the fact that it was kind of characteristic of a carbureted engine and the fact that it was a Holley on top of that. Now, I am wondering if maybe the intake could be contributing to the problem. Any input is appreciated.

Bill

[Bill usn-1]

I'm not seeing anything real bad.

Do you still have an egr mounted on the manifold?

[bkshir]

No. It isn't even ported for an EGR valve. It's an aftermarket, performance style intake, but there is no brand or distinguishing markings on it, so I don't really know much about it. It was on the engine when I bought it. I don't see anything really out of line in the data either, even on the runs I've made when it was cold and running poorly. That's why I was wondering if I should be looking elsewhere for problems. You've helped me make vast improvements and I really appreciate it. Just wish I could nail down the source of this one last issue.

Thanks again,
Bill

[Bill usn-1]

What timing are you running?
Is it still running your old distr?
Have you checked the timing at idle and then every 500-1000rpm and see what your max timing is?

The hesitation sounds like it's fuel related but the numbers don't look that bad.
You may be retarded or slow on the timing.