Erratic engine - need a little help

[dyazdani]

My 92 Explorer (all of a sudden) starting acting strange on the way to work this morning.

The CEL came on when I started up, didn't really notice any issues for about a mile. Then, while under power, the RPMs would increase then level out and this would repeat.

When I got to the light right before work (I have about a 3-mile drive) the engine died when I came to a stop. It started right back up and I can seem to keep it running with a little gas.

I've done some searches and will clean the MAF and check out the IAC if I can get it back home. I also read the EEC thread to learn how to read the codes if the local AutoZone can't do it. The fuel filter, air filter, plugs, and wires are fairly new (within a year or so old).

Can anyone point me in the right direction based on the symptoms? I'll do some more troubleshooting later, my luck this would happen on the way TO work instead of FROM work...

 

[little x]

You just need to read those codes first. I would guess the O2 sensor, since it runs fine at first (when the computer uses a set fuel mapping) and then once it warms up it begins using the O2 sensor and dies. But the codes will tell you what's up.

 

[dyazdani]

You just need to read those codes first.

I had the chance to read the codes, here's what I got:

KOEO Codes:
159 - MAF sensor is/was out of range - MAF

CM Codes:
157 - Mass Air Flow signal is/was low or grounded - MAF
158 - MAF sensor is/was high or short to power - MAF

I pulled the MAF and it looked like it was in good shape as far as being clean. Obviously, something is not right with it. Does this mean a new one? I'll do a search in the meantime and see what's up.

TIA

 

[little x]

CLEAN it. I can't tell you what a big difference it will make. Don't wast $300 on a new one. BTW, if you do clean it and it's still out of wack I have 2 spare maf's and I'll def. sell you one if your interested. But first try cleaning yours.

 

[dyazdani]

Did a little more fooling around - first, after I checked out the MAF the first time, I forgot to put the harness back on. I fixed that and re-ran the tests, including a KOER.

KOEO codes:
111 - pass

CM codes:
157, 158 as before

KOER codes:
998 - I read somewhere that seemed to indicate this might have been because I didn't get a 111 KOEO code first.
157 again


I cleaned the MAF and the IAC with carb cleaner and put them back. Started it back up and it ran rough for a bit (carb cleaner in the intake I think) but then leveled out. The CEL went off and stayed off, for now anyways. I'll see how it goes tomorrow. I think I'll erase the memory first and see how it goes.

 

[dyazdani]

I took a spin for a few miles - the idle is much better. The CEL was off for a mile or two and then accelerating out of a turn, there was a minor hesitation and the CEL came back on. It went off a few (maybe 20 seconds later) and stayed off for another mile or two until the same thing happened (slight hesitation).

I'll read the codes again tomorrow and see what they say.

 

[vrytired]

pull off that black plastic tube that goes from the MAF to the throttle body and check it for cracks at the flexible parts. electrical tape works goof for sealing it up. if the engines sucking in to much unmetered air the MAF will read low.

 

[dyazdani]

It was back to the same old thing this morning. I'll re-read the codes this afternoon and post the results.

 

[dyazdani]

I read a fresh set of codes this afternoon:
KOEO: 111 - OK

CM: 157 - Mass Air Flow signal is/was low or grounded - MAF

KOER: 157 - Mass Air Flow signal is/was low or grounded - MAF

I cleaned the MAF and the IAC but it didn't really help much. Is there anything left to check before changing out the MAF?

What about testing the output of the MAF? I'll have to find a wiring diagram somewhere - I'll try searching.

 

[nismotunedgtr]

Did you disconnect the battery for atleast 15 minutes after cleaning the MAF?

Carb cleaner is not good for it, buy a can of MAF clenaer.

 

[dyazdani]

Did you disconnect the battery for atleast 15 minutes after cleaning the MAF?

Carb cleaner is not good for it, buy a can of MAF clenaer.

I reset the codes after cleaning it, yes. I used the CRC electronic cleaner. I used the carb cleaner on the IAC, I originally mistyped it...

 

[dyazdani]

I did some more testing today: I tested the response of the TPS with a voltmeter, it was normal - ranged smoothly from 0.8V - 4.5V as I increased throttle.

I also tested the supply to the MAF, it read normal at ~11.8V. The signal back from the MAF read around 0.75V at idle and seemed to respond correctly when I bumped the throttle.

This puzzles me since I got the 157 code. Any ideas?

 

[410Fortune]

P0157 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

Sounds like your S2 B2 02 sensor may be faulty, check its wiring
This is a catalyst monitor sensor and since the computer code is a low voltage problem it is quite possible its time for a new 02 sensor.

 

[dyazdani]

P0157 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

Sounds like your S2 B2 02 sensor may be faulty, check its wiring
This is a catalyst monitor sensor and since the computer code is a low voltage problem it is quite possible its time for a new 02 sensor.

This is an EEC-IV 3 digit code "Mass Air Flow signal is/was low or grounded - MAF" I think the Pxxxx codes come from the OBDII readers...

 

[410Fortune]

OH MY BAD 92 truck I am getting too used to dealing with EEC-IV

If this is the only code you are still getting it may be time for a new MAS, can you swap it out with a known good MAS from a 4.0L ranger or Explorer 91-92?

 

[dyazdani]

I tested the fuel pressure at the rail - 42psi with KOEO, 35psi with engine running, stays within 1-2 psi of that point when throttle is increased. I disconnected the vacuum line from the FPR and the pressure increased by 8psi or so. Fuel seems like it's OK.

The engine dies with or without the MAF plugged in. Like I said, the voltages to and from the MAF look normal. I'm going to clear the codes and read them again to verify.

 

[1shot]

maf plugged

I dont think a bad or miss-behaving maf alone should kill yer truck.

I forgot to replug the connector on my maf a few days ago when I was installing new air filter.
I drove home with stereo blasting but thought I heard a ping or two on a hill. When I pulled in my driveway I saw the "Check Engine" light was on and I suddenly remembered the MAF plug. With a embarrassed look on my face I lifted the hood and yup - it was just hanging. I plugged it back in, restarted truck and the "Check Engine" light did not come on.

Point of story is - even with the plug completely off, my truck still runs. Maybe you have something else happening?

 

[mawrazen]

Have you checked all of your vacuum lines for leaks, cracks or diconnects?

 

[BeetleBailey]

Might also double check your "Plug Wires and Plugs". Sounds like you have a definate miss somewhere. JM.02 Bailey.

 

[99xploder]

99 4.0 with the same problem. However driving down the road it will buck every once in while. I cleaned the IAC and replaced the MAF. Running short of ideas other than making a bon fire out of the thing. Tomorrow I will replace the TPS. Any other suggestions would be appreciated!