Ok...I was a automatic tranny mechanic for a number of years and drivetrain troubleshooting is my bag...but I never worked on fuel/ignition systems and need some help.

I read a lot of the posts related to my problem on this forum and it has been extremely helpful....but I need some additional help

I have a 98 explorer sport 4.0L EFI that has about 170K miles on it. It has been a good vehicle and now seems to be having issues. I parked it for about 2 weeks over xmas break and when I drove it afterward it began to miss and stumble under load and also idle rough. The CEL came on and when I drove home, the CEL began to flash.

The next day I took the vehicle over to my friends shop and he let me put his snap-on scanner on it and check for codes. There were a three codes stored. One was a cylinder 3 misfire code and P0171/P0174 both banks lean codes.

I did a brief check under the hood and didn't see any obvious hoses disconnected and decided to clear the codes and take it home to do a more thorough inspection. I cleared the codes and drove it home. It continued to run rough on the way home and there was no change. The CEL came back on but it did not flash this time.

I did some reading here and checked a few things.

I pulled the tranny out a couple months back to repair a leaking throw out bearing slave cylinder and disconnected the o2 sensors when I pulled the exhaust and crossmember for tranny access. I thought maybe an o2 sensor might have gone bad or i did not reconnect one of them well enough.But when reading the forums this appears unlikely since both banks are lean....seems like two sensors going out simultaneously is unlikely? and my condition would not be cause by disconnected o2 wire harness. Please elaborate if I am off base....

First I checked the air filter....and discovered that the air cleaner cover was not clamped down and was loose (stupid 19 dollar Jiffy lube people were last people to check that around 4 months back..so they must have forgot to close it). There was a few leaves inside the air cleaner housing and the filter was dirty. I replaced the air filter, cleaned out housing and made sure the cover was secure. A post here suggested that an air leak in front of Mass Airflow Sensor could cause my condition. I cleared the codes and drove it and there was no change at all....still runs rough...(no CEL or immediate codes so far) I also checked the intake "snorkle" from air cleaner to make sure no leaks there...

next I got some Mass Airflow Sensor cleaner and cleaned the sensor because the loose air cleaner cover might have allowed filament to get dirty........but there was no change after I cleaned it.

Below is a checklist I found that I am going over before I take it back to my friends shop...but I have a few questions.

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P0171/P0174:

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel. (use a fuel pressure gauge to check fuel pressure at idle)
See question below
* Dirty fuel injectors. (try cleaning the injectors)
See question below
* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)
See question below
* Leaky EGR valve. (Check operation of EGR valve)
See question below
* Leaky PCV Valve or hose. (Check valve and hose connections)
I checked this and the hose was good and did not see any other bad hoses

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning thewires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)
I checked this and cleaned it according to forum recommendations....
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Ok...so I have questions to help complete the checklist....

1) how do I check the EGR valve? I searched the forum and other places and could not find specific info on how to do that....there is no obvious rust or other outside deterioration on the EGR.

2) vacuum leaks

I checked the entire vacuum system under the hood as best I could for vacuum leaks and could not find obvious leaks or bad hoses. I plan on going and using a vacuum gauge to check for low pressure reading to rule this out. What is the normal vacuum pressure reading?

Furthermore...Recently (at around same time vehicle was parked for two weeks) it has rained and the temperature was dropped to just above freezing. I live in a desert area and I read how the intake manifold gaskets are a major problem with this engine and can shrink and cause the both banks lean codes when cold due to unregulated air leaking. However, there was no change when the engine warms up that would obviously point to this (gaskets/o-rings expanding when warm)I sprayed carb cleaner around the intake to see if it would cause a change in idle (indicating this type of leak) but it didn't seem to change the rough idle either way. but if there is a low vacuum reading (when i use gauge and check) I will keep this in mind.....

Where is best place to connect vacuum gauge and what readings should i look for?

3) Where to connect fuel pressure gauge and what reading should i look for? This problem seems unlikely to me, but I am not ruling anything out. Maybe fuel filter is clogged?

4) Fuel injectors need to be cleaned using additive? I know this requires a tank of gas and a bottle of something from auto parts store....but do you think this is a realistic cause? i will dig deeper into this if I rule everything else out....

Any help and guidance would be appreciated....

A final observation......and a strange one

When i was leaning on the car looking and listening for vacuum leaks....I got moderately shocked when i touched the frame and created a circuit with my body by touching another put of the engine compartment. It felt like a spark plug shock that pulsated and was fairly powerful..it got my attention!! I checked the spark plug wires and they all appeared to be connected well and I especially looked at #3 (one with bad code) but didnt see any obvious problems. Perhaps this indicates another problem?? Dont laugh....but I got shocked when I touched the heater hose (I know..its rubber and not part of ignition system...so this perplexes me)

I am going to replace spark plugs....since i have a new set in my toolbox anyway and they needed to be changed and i will tell you if plugs are fouled....

Thanks for any help...i know my way around drivetrains and such..but engine top ends are not my forte...

 

sounds to me like you have some leaking intake gaskets (lower need to repalce both upper and lower). for the 171 174 code or you have a busted pcv line. the cyl 3 misfire code is proablly a plug wire or possible a coil. swap to wires and see what happens.
glad to see someone else on here likes trans work

 

Negative on the intake manifold gasket leaking....did a vacuum test and its steady at 21Lbs (normal is 17-22)
Im going to change plugs and see if there is a fouled plug (forum post suggested that lean banks code could be caused by fouled plug)

and now to check other issues

any suggestions??

 

Couple of items from my brain.

Being a 98 with 170K, I would replace the plugs and wires. Ensure that you use dielectrical grease on the plug ends and in bothe ends of the wire boots. This will greatly reduce and chance of spark leakage.

Since you have a rough idle and running condition, I would also check the IAC (Idle Air Controller) and the DPFE. The DPFE module is also a known problem as they are exposed to high exhaust temps and moisture. These tend to corrode internally and can cause EGR issues without popping a code.

 

you cant really go by a vacuum test because the intake gaskets will leak in the am when they are cold and suck in air. a maf sensor will also cause the 174 171 codes

use common sense also has a good point

 

thx for the input ralphie...but...

I checked vacuum when engine was cold and it was running rough when i checked vacuum, so i don't believe it is a vacuum leak from manifold o-rings. In fact..the 21lb reading leads me to believe this isn't a vacuum leak at all...but something else entirely..vacuum operated fine when i revved motor....no strange vacuum readings or operation...

Heres a question....

I took apart MAF and cleaned the filament with MAF cleanner by spraying it with cleaner. Do I need to use a Q-tip and wipe the filament directly? I realize it is very fragile, but I though just spraying it twice and letting dry would suffice?

thx for the feedback...

 

thx common..ill check it

I found the following method to check it...enlighten me if it is wrong method to check IAC operation

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To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< <<<<<<<<<<<<<<<<<<

 

common...what is best way to check DPFE without throwing parts at it? can i unplug harness and check for change in engine running condition or something?

thanks for help

 

That will work for the IAC. I clean them out with carb cleaner. As far as the DPFE, just remove it from the two silicone hoses and tap it in your hand to see if any moisture and or crud comes out of either tube. If so, it's probably corroded and the electronics shot. You can disconnect the connector and start the engine to see what running change there is. A failing DPFE can also cause extended crank time/hard starting issues also.

 

update....

Changed out the plugs and found a few of them that were in bad shape.

I took off IAC and when i turned ignition on it appeared to be froze up and wouldnt move at all. Also had lots of black deposit buildup. I cleaned if out with some WD-40 and carb cleaner and it appeared to move a little when ignition turned on.

Jumped in and started it up and it runs 100% better. No miss and doesnt stumble anymore. Gonna drive it to work tommorrow and cross my fingers that no more codes pop up.

probably a combo of bad plugs and stuck IAC I guess...

thanks for the help everyone...