B2 Swap 4.0 High Idle, Running Rich.

[Hahnsb2]

94 4.0, When started idles around 2500 RPMs then over time will drop to 1500 RPMs. Changed MAF, and IAC, both from previously good running explorers (Mine also ran very well before pulled). Vacuum sits at 21" steady at "idle" and I can't find any vacuum leaks with my ears or spraying carb cleaner around the intake. It smells very rich, to point it almost burns your eyes. I hooked up all sensors that should be needed. Would a TPS cause this? I havn't changed it yet since the screws are frozen solid. I may try pulling codes if I can find the CEL wire and hook it up to my dash (Don't have an analog meter to test with).

 

[Hahnsb2]

I think I've determined the idle is about normal since it's showing me 3500 RPMs in 5th at 55... So my tach is off, something still doesn't seem right. Took it to schucks and hooked up the code reader, only KOEO code was 522 not in nuetral during test (none of the tranny wires are hooked up). Wouldn't pull any KOER codes....

 

[Ranger44]

What about the O2 sensor or ECT?

Both are important to feedback. A bad ETC usually will tell the computer that the engine is at -38*(default). Making the engine think it's cold, and it dumps fuel into the engine to warm it up.

A bad O2 sensor can also screw with the fuel trims.....

 

[Hahnsb2]

Do you know where I can find test procedures for the various sensors (only found the MAF proceedure in the tech library)? MAF checks out and I cleaned it with MAF cleaner. I have a DVOM so I'd like to check teh O2 sensors (Both look pretty fresh) and IAT and ECT sensors. I also have that backpressure sensor for the EGR as well.

 

[Ranger44]

Best bet would be a chilton's. What year is your engine?

 

[Hahnsb2]

94, I have a chiltons for it, mainly used it for the wiring harness, I'll check it out.

 

[Hahnsb2]

Put the 4.0 though it's first real test a bit ago. Driving down the road, following some old hag in an Olds 442 convertable doing 25 in a 40, we both take right at the intersectiong onto a road where we have 2 lanes and merges to one in less than a 1/4 mile, so since she was going slow, after the corner I whip out into the left lane and start getting on it hard, she punched it too trying to beat me to the lane merge, we were neck and neck till around 60 MPH then she let off But as a result on getting on it hard I had a couple random misses shortly after, I suspect the O2 sensors.

 

[Hahnsb2]

Also a couple ocasions I've noticed while reving the engine (while not moving) to around 2500 RPMs (guessing) and hold it there, after about 10 seconds it will start to miss on what sounds like all cylinders randomly, I've only been able to replicate this a couple times, both the IAT and ECT sensors checked fine, I'm probably going to replace the O2sensors regardless, they arent too expensive.

 

[Ranger44]

I was taught to replace all major sensors when doing an engine swap.

This is from a shop mentality though. It's better to do it now and have the customer happy the first time, than have the customer come back again or 3, 4, 5 times. Making an unhappy customer. This is also because you have no idea on the running history of a customers vehicle.

But if it's your own, you only have yourself to blame....lol

Hopefully the O2 sensors fix the problem.....

 

[Hahnsb2]

Well I've replaced both of them (goddamn whovever decided to put the passenger sensor where it is was smoking crack, nearly impossible without a ratchet wrench), didn't notice any hiccups when I drove it to the auto parts store to get them. That leaves me with the TPS and DPFE. Do you know the testing proceedure for the TPS? Chiltons wants me to use some special BS connector that goes in between the computer and harness, I probed the wires but was getting something like 4 volts which is way higher than the .9 spec, so I'm not sure if I actually need to test the wires at the computer.

 

[Ranger44]

Hmmm, I was taught to back probe the conector and check the voltage at idle, 1/4, 1/2, 3/4 and WOT. It should climb steadily. Such as if you drew a graph, the reading should be a straight diagonal line in a sense. And to watch for dead spots....

Can't remember, but pretty sure it was KOEO.

I performed the excersise on a 2001 exploder with a 5.0.

A TPS would cause stumbling when you mash it /accelerate. It's a 100% driver input sensor that has something like a 500% over ride on the injectors. Basically it will increase flow instantly, then once the other sensors catch up the CPU will regulate the injectors.

 

[Hahnsb2]

Well it's supposed to have a .9 volts when closed which is adjusted by the screw on the throttle body (at least on the 2.9, 4.0 looks the same) and any change in the idle caused by the adjusting screw should be taken care of by the IAC. I've tested the resitance through the sensor while slowly opening the throttle and it's smooth with no sudden jumps.

 

[Ranger44]

any bad grounds? lol

How's it running now?

 

[Hahnsb2]

Running pretty good. Yesterday I broke the tires loose at 40MPH in the rian and right after I did that the RPMs didn't want to come down for a few minutes, it stayed hovering around 2500 RPMs. Figured out that the nuetral sensing switch was not letting it pull KOER codes since it wasn't hoked up, I hooked it up and hooked a scanner to it and scanned it and there's no codes present. I didn't have the ground strap hooked up on the engine for the first few days either, just the negative battery cable, so that's hooked up as well now.

 

[Ranger44]

Hmmm. I can't wait to swap in a 4.0.....

It wouldn't store any codes till it got through a few full running cycles with the same thing happening.

Is this a non-egr 4.0?

Not really sure what else will be causing this......