New plugs and wires = won't idle... Hmm.

[962drrhino]

winterbeater
can you actually "quickly" diagnose sensors by just unplugging them, simply "bipassing" the sensor letting the computer take over?
I see some of the fellas in here talk about it. I actually was told this by a chrysler mechanic, he said that some of the sensors, (not all) would let you do this. I think this conversation was basically about my MAP sensor.

I never had the chance to try it, but do you think this would help him out?

 

[winterbeater]

I really can't say for sure, but that makes sense. If a sensor goes into it's normal failure mode, you want to be able to get home. I guess that if you inplug it and it gets better, that proves a bad sensor. If it get's worse, the sensor is probably OK. If no change, you can't tell anything. Without the CKP, it won't run. Without the temp sensor, it won't enrich for cold starts, not sure about MAP, but my guess would be that you are right.

 

[winterbeater]

How to test a MAP sensor: http://www.youtube.com/watch?v=B8EVhFc5Yqw

Thanks to wim showing us the you tube connections to car repair.

 

[Mr. Ninja]

I think it depends on the sensor. Obviously the more "important" sensors IE MAP and TPS may have a very adverse effect on how the car drives, and in some cases depending on the engine management, will make the car undriveable.

Also, a fun update as to where I'm at:

TPS: good (tested damn near balls on to spec)

CPS: good(new, old one was missing the bolts and the wires were a bit chowed)

IAC: appears to be working properly, also cleaned.

EGR: appears to be working properly, moving freely under vacuum/acceleration

MAP: tested barely inside spec, but still within spec.

O2: good (new)

cap/rotor/plugs/wires: good (new)

vac lines: from what I can see and have been over multiple times are all good

fuel pump relay/underhood relays: good (swapped all 4 with known good relays with no change)


only thing left that I haven't been able to test is fuel pressure/delivery. I need to go buy a fuel pressure tester and see whats up there. Still seems odd that it'd be a fueling issue when the misfiring/lag goes away after 2500 RPMs, at which point it seems to be running fine. I'm wondering if fuel delivery is at a maximum at the sub 2500 rpms when the engine is really trying to put out some torque.

I'm not too annoyed about all this cause there have been some noticeable positive differences with some of the things that have been changed, so I think once I figure out what the main problem is and fix it, it'll be running like a raped ape.

Anything I'm missing or should double/triple/quadruple check?

 

[scottmcneal]

Firing order right? Don't ask..

 

[orange]

Give autozone or your locals a call. Some rent/loan tools and probably fuel pressure gauges too.

--

Vaccuum gauge too!

That will verify both systems - one trip.

 

[joe_peters]

Rent the fuel gauge at a chain auto parts store.

Just for grins and giggles, what is your battery voltage at idle? Should see 13.6+

 

[winterbeater]

I'm not saying don't test it, but if you are going 2500rpms and floor it and run it up to redline without problems, it sure doesn't seem like fuel problem.

 

[orange]

(Memory aid-Shamelessly stolen from somewhere)
-----------
Firing order 6 cyl. 4.0l

15 - too young
36 - too old
24 - just right

153624

 

[winterbeater]

Reread whole thread. When in doubt, why not check compression? You don't say your mileage, but it is a 1990. No point chasing more shit until compression is verified.

 

[winterbeater]

(Memory aid-Shamelessly stolen from somewhere)
-----------
Firing order 6 cyl. 4.0l

15 - too young
36 - too old
24 - just right

153624

Last one I got was 19 and she is still just right. And that was 1971. :yelclap:

 

[orange]

Thanks winterbeater,

fuel, vac, compression - that makes three gauges to rent!!!

 

[Mr. Ninja]

iring order is good, one of the first things i checked after i had issues when i did the wires originally.

i may do the compression test at some point, but this is a fresh-ish motor (rebuilt 20k ago) and aside from slightly stumbling in this limited rpm range, it runs/ran great.

I'll prolly just buy the fuel pressure tester. I like tools and there have been times I wished I had it before. Plus my snap-on account is pretty low right now .

batt voltage is good...actually more like great. ;-)

probably wouldn't hurt to pick up a vac guage/tester too, since my last one mysteriously went missing this summer while I was away in AK.

 

[Mr. Ninja]

Yee haw.

Well finally picked up a fuel pressure tester kit.

I'm sitting around 20-30psi during idle, no difference if i unplug the FPR or not. When I accelerate it bounces around sometimes spiking up to 39psi.

Sounds like the pump, but any chance that its the FPR?

 

[winterbeater]

Pressure needs to be above 44.2. Pump must be bad. Failure mode of FPR is too high pressure. I suppose you could block it off return line and test again to make sure.