calling all shade tree mechanics..

[tdavis]

Ok, so I took the ol' 93 navajo out for a drive the other day. For those who remember, when I drove to Moab, it over heated, and started to have stumbling/hestation problems when I got to moab. I haven't fixed it yet, simply because I'm reluctant to do 'sensor of the day' repairs, and wanted to see if I waited long enough, the culprit part would die.
I did however, get to swap a known good mass air sensor in one time, and the problem still existed.

Ok, back to the road trip. The truck's check engine light came on, and off.. and so on, until I got home. The truck will also stumble, and hesitate also at this point when given partial throttle, under load (ie, between 1k and 2.5k rpms, in 5th gear). The truck runs perfectly fine until this occurs. This doesn't occur until the truck has completly warmed up (it takes about 20 minutes of driving). Temp is just into the normal range (which is 'normal' for this truck).

So I pulled over, and hooked up the test jumper, and started to read codes.

I got from the computer:

172 - lean condition, right side
176 - lean condition, left side
185 - mass air flow lower than expected
186 - injector pulse width lower than expected
172
176
185
186

I also hooked up a fuel pressure gauge, and got 40lbs of pressure engine off, 30 running, 40 w/vacum line pulled from the regulator. (which is in spec)

Ok, so I'm thinking it's a bad Throttle Position Sensor. (Mac also is guessing that - he played with it a Hollister before he left, and thought it was acting slow to respond to the gas pedal) Here's the deal - before I take it in, let's see who can guess what's wrong!

Ok boys, I'm ready for ideas.

 

[Tom Wilk]

Throttle position sensor is a good candidate. A vacuum leak is another. Carefully inspect all your vac plumbing before shelling out $$. And, you might as well clean the MAF even though you effectively eliminated it as a cause by substitution. It won't hurt.

There could also be a problem with the EGR valve, though this should give you a computer trouble code of its own. I'd take a look and make sure it isn't gummed up or sticking or something. You may be sucking in some exhaust gas through the valve that will give the symptoms similar to a vacuum leak.

[Edited by Tom Wilk on 06-12-2000 at 11:44 PM]

 

[shane]

I agree the TPS is the sensor I would also check first. I had the same problem with a bronco II.

 

[Lobo]

How would you test the Throttle Position Sensor? I have had similar symptoms.

 

[Gofast]

I'm going to go the complete other way...I think the O2's are toast. I got lean condition codes with my O2's. A lean condition will run hotter too. Replaced my 02's and no more check engine lights. The computer will also try to compensate for lean conditions and may cause other codes to light up. And wouldn't a low MAS reading indicate less air and thus cause a rich condition by not supplying the expected amount of air for the fuel ratio?

Wow, my head hurts now.

I reserve the right to change my answers to whatever the right answer is, therby saving my self-esteem.

 

[Maniak]

Lobo,
Here is a link for instructions on testing the TPS

http://mark.legendz.com/code124.html

 

[shane]

Gofast, how do you like your EZ-LOCKER I was thinking of getting one.


Back to the tps. To test the tps you use a om meter undo the wires on the tps hook up the meter dont start your explorer and work the throtle up and down and see if it shows a dead spot. The tps should read smooth up and down if not you need to replace it.

 

[Tnewcomb]

Had same problem including taking the time to warm up. O2 sensors. Good luck.

Tim

 

[tdavis]

Sorry, forgot to say that the O2's and cat's have been replaced, and it still exhibits the problems.

Maniak - hey, that's information I'm looking for! Thanks! Where did you get this from?

[Edited by tdavis on 06-13-2000 at 10:52 AM]

 

[tdavis]

update!

Alrighty!

Taking what Maniac put on his web page, I started testing tonight. My only problem - it's hot today in Oakland (about 85-90 degrees where I'm at).

But, the TPS appears to be working.

The ACT on the other hand appears to be bad. It reads low when cold - 2.25volts, and then reads high when warm - 1.75v

I'm going to replace it and see if it helps any!

 

[Maniak]

I ran across this info when we had a problem with our explorer stalling when the motor was cold. I don't remember where I got this piece of info.. but it was the same place that explained the AIC (or IAC.. whatever the offical name is) is actually what keeps the engine idle up when the load changes.

I'm still looking for the actual steps to test the AIC(IAC) so I can put that up also (they are somewhere in my pile of notes)..

 

[kilroy]

If your talking about the Intake Air sensor, here is how to test it.

Test the IAC with an ohm meter. High reading when cold, 68 degrees F the resistance is 27.30K ohms, Low reading when warm, 212 degrees F 2.07K ohms.

A note, if this sensor is bad it will set a code of 112, 113, or 114.

 

[Maniak]

I dont' think the AIC and Air intake sensor are the same things.. The Air intake sensor is the Air temp sensor on in the plenum near the fire wall while the AIC (IAC) is what controls the idle speeds by allowing air to bypass the throttle plate.

 

[91Explorer]

Maybe you have a bad igition module or coil (1/3 or the coil is no good which would affect 2 cylinders). I'm leaning toward the module though, because alot of times modules would work fine when cold and act up when it gets hot until it finally quits.

 

[tdavis]

have you seen this?

Ok, so I was doing more research today. Found this url:

http://dalidesign.com/hbook/eectest.html

Has anybody ever used this book? Is it worth the $30 pop for it? (I'm thinking about doing it, esp. if helps me figure out the problem, without dumping a ton of money on a shop to diddly around with the truck..)

As for the sensor/ignition module, I know of someone who has a spare module (Gi - can I borrow it?) and I haven't called anyone about the sensor (it seems to be reading high - which could throw things off)

 

[Big E]

I have been reading all of the posts here. I really don't think it is the coil pack. Yeah they go bad or act up when hot but how many do you see replaced cause they need to be. Can you give some more clues or info. But from what I can tell. It sounds like the ecm is telling the engine to run rich cause of the o2 sensor reading lean. But with the MASS sensor reading lower than normal. Check to make sure there are no restrictions in the air intake. Make sure the gaskets are all ok. Try spraying some carb cleaner along the instake gaskets. And listen for a stumble. And if that dosen't solve it. I will have to think some more. And while you are checking things make sure you check the pcv valve make sure it rattles. and if it does it still might be bad. I have had one from ....Auto Zone....please don't beat me. It was bad when it rattled. I went to Ford and got a new one. No problem. I think I would start there. I hope this all makes sense. I am going to college for this kinda stuff so maybe it will pay off. Keep us posted.

Eric

 

[BenA]

IAC (Idle Air Control valve)

To test the Idle Air Control valve:

A) Turn ignition OFF

B) Remove harness connector from IAC valve

C) Measure resistance across termiinals

Note: There is a forward biased diode in the solenoid. When checking the resistance, make sure the POSITIVE lead of your VOM is on the VPWR terminal, and NEGATIVE on ISC terminal.

There is a gasket that is on the IAC, so depending on the condition of the gasket, you may be faced with replacing the gasket it you remove the valve.

Ben

*****************************************
P.S. Hey Kilroy,

Your specs are for the IAT (Intake Air Temp) Sensor, not the IAC (Idle Air Control) valve.

Ben
******************************************

[Edited by BenA on 06-15-2000 at 11:06 PM]

 

[tdavis]

It's fixed.

Well, took it in today.

Got it back, $225 poorer.

But it's fixed. You won't believe what it was.

The spark plugs. I had put brand new bosch platinum plugs in before Moab, and they had blown the tips off of themselves.

So add to the list: when hestating, replace plugs.

 

[Gofast]

I herby excersize my right to change my answer. I thought it was the plugs too.

Glad you got it fixed. It's always a good feeling to get one of those nagging problems fixed. I'll have to file this one away for things to check after a tune up. The codes it was throwing definatly lead us in other directions.

 

[Tom Wilk]

Glad to hear that the problem has been solved. But, plugs for $225?? I hope they did some serious troubleshooting for that much money. Goes to show you, it's always something simple. Well, with the computer codes and all, it didn't appear to be simple at all.

I also want to change my answer.

Honestly, I'm a firm beleiver in doing the cheapest repair first. Ya know, clean the MAF, clean the EGR, that kind of thing. Plugs would have fit that bill, I'm afraid, but the thought never came to mind.