Troublesome Trouble Codes

[zebadoba]

Hello fellow Explori,

I have been working on check engine light for the last two weeks and am stumped and would love some advice. I have a 1994 Mazda Navajo with 127k, bone stock.

Check engine light came on one day and she started to run rough at idle, RPMs would drop, voltage gauge would flicker. Then two days later engine was much more rough at idle and during driving and I was smoking like a coal fired locomotive.

Pulled the codes 157 & 158 (MAF below minimum voltage and MAF above maximum voltage) KOEO (memory) and 157 & 998 ER. This is where I thought “Ah ha! My first trouble code and it is easy!” Replaced the MAF – no change in performance.

Dug a little deeper in the forum’s past post and discovered the vacuum line to the Fuel Pressure Regulator was off (old rubber), “Ah ha!”; no change.

Then I checked the fuel pressure at the fuel rail. Everything within spec per my Haynes manual (31 psi @ idle w/ vacuum – 41 psi @ idle w/o vacuum, held 41 psi engine off).

Checked the IAC valve (voltage and resistance) all ok. Climbed all over the engine looking for loose connectors and vacuum lines; all ok.

Drove it for a week. Smoking like a train stopped, I could drive about 3 miles w/o a check engine light, then the engine would shudder a bit and I would be back to code 157 and knocking like crazy. At stop lights, in drive, the RPMs would drop and the voltage gauge will flicker and the exhaust stinks. About 50% of the time when starting from idle there will be a serious lack of power for 1 ~ 2 seconds, then she will come on strong and go go go.

Double checking everything today, I pulled a code of 124 (TPS voltage higher than expected ) and 157 (KOEO memory). First time I have seen 124.

The first part of seeking advice is better instructions for testing the MAF with a DVM. I read the Haynes’ instructions and have 12 at the B+ to first ground (on the left) 5.8V from B+ to the second ground. Then the instructions get sketchy as to what I should be seeing when I reconnect it and test it with the engine running.

Second part of seeking advice is what next?

Thanks,

Andy-

 

[MrShorty]

1st question: Did you get a KOEO 111 pass code? If not, could you identify which code(s) were output as KOEO codes and which were CM codes? If you need help explaining the terms, review my "notes on pulling EEC-IV codes" thread. I'm getting a little bit of conflicting information from my code lists as to which type of codes 157 and 158 can be. Since a KOEO code would have to be electrical, it would be the place to start.

As for further testing instructions, have you tried Chiltons (see the vehicle repair guides at www.autozone.com

 

[zebadoba]

Thanks for the quick reply.

You thread on pulling codes was a big help when I started this project! It started me in the right direction. Thanks for posting it. I am going to go back and do the whole test, as I was just pulling the codes with the ER then shutting down.

Clarification on my first post:
The KOnEOff codes (157, 158 & 124) are CM or post 111 codes. The ER codes (157 & 998) are EngineRunning. Codes were pulled with a jumper clip and check engine light count.

I will make a run to the Library check out the Chiltons and see how it differs from my Haynes manual. If it looks worth while I will pick one up.

Andy-

 

[MrShorty]

Your situation sounds a lot like one that was posted within the last few months here. He ended up replacing the MAF in a "guess and check" attempt, and it fixed his problem. It would be interesting to see what the MAF is outputting (both KOEO and KOER) that causes this kind of behavior.

 

[zebadoba]

Reran all my test with my two year old assistant. She sat shotgun and drew all over my registration and insurance forms.

KOEO:111
KOER: 998 & 157
CM:157

But in the KOER test she would not do the low speed and high speed part of the test. As soon as I started her I would get 998 & 157 (twice) and then she would just sit there with the CEL on and idle at about 700 RPM. We waited and waited but nothing happened. Goosed her to be on the safe side, and she just sat there with the CEL on. When we got out there is a huge soot slick on the drive way!

We replaced the MAF last week with one from NAPA. It was the first thing we did.

Any insights?

Andy-

 

[zebadoba]

Well took Maru in to the Ford Dealership as I was tired of blowing smoke an running poorly. Have a new "New Style" MAF and new plug and wiring assembly. It was expensive, but I wanted someone who has seen lots of these, and knows the Ford EEC system inside and out.

It is interesting as in my write up, they said " RAN MAF TEST AND FOUND CONNECTOR LOOSE AND MAF SENSOR AT 146HZ. R/R SENSOR AND PUT NEW CONNECTOR ON. CLEAR CODE AND ALL GOOD. MAF AT 159HZ"

I could barley test for battery voltage at the sensor, much less notice the difference between 146 and 159Hz.

So far everything is good. I did all my previous physical tests; hot engine, cold engine, drove over a bunch of concrete to flex the wiring harness, WOT, idle in drive without any CELs or or poor performance.

Andy-