Mike Frye

My car ran rough once or twice last week, which is VERY uncharacteristic. Still drivable, but round accelerating. I thought it was a ground problem because it had been rainy and I hadn't cleaned the grounds recently. When I shut it down and let it sit it would run fine the next time.


Then the other day I get in and it's idling like crap. I had to go somewhere so I shut it down and took my other car. It was STINKING rich too at this point.

Next day I go out to take a look at it and same thing. Idling like crap, won't come up off of idle and it smells rich as hell.

I think it's in limp-home mode and that my MAF has finally given up the ghost but I want to confirm this before going down the rebuild route (which it needs anyway, but I'd rather not get it back and THEN find out I have more work to do).

I took a reading at the MAF on pins 3-6 where I think it's supposed to read 382 as a default. My notes show that the last time I adjusted it, I left it at 272, which gave me a perfect 14.7 AFR at warm idle.

Now it reads 252 at the MAF.

When I read pins 6 and 7 on the LH plug with the MAF plugged in I get a dead short. It's wide open with the MAF unplugged.

I think LH plug pins 6 and 7 are the right pins to check for MAF resistance.


Can anyone confirm that...
A) this is the right place to meter it and I should be getting the same reading at LH pins 6 and 7 that I get on 3 and 6 on the MAF? and
2) that a failed MAF will do this (show proper resistance on 3-6 when not plugged in, but show a dead short at the LH plug when the MAF plug is plugged in)?


I think my tests are good, but if I'm missing something or I've gotten it wrong please let me know.

SeanR

There's no limp home mode until '90 or so. Check the wiring under the boot on the Temp II. The measurements you are taking on the MAF are not that far out so it would not be the cause here. I'd try to find a good used MAF to swap in and see if it changes before you go get a rebuilt one.

Mike Frye

Sean,

That's what I thought too, but I got educated two months ago and now my car has decided that it needed to prove it.

I did some research in the '85 LH test program and it talks about this as well except it's actually 2K rpms that the timing changes, not 4k. Other than that Mr. Speake speaks the truth.

I did think about the known good MAF though. Anyone got one I can borrow?

Mrmerlin

I would pull the vacuum lines off the dampers and the FPR its about time for them to fail if one smells like fuel then replace all three.
The dead short info is concerning However IIRC those are not the pins you measure,
Hold on let me search


Read this ,

https://rennlist.com/forums/928-foru...MAF+adjustment

Mrmerlin

Something else to look at iare both of the coil wire connections ,
make sure neither of them are rubbing on any part of their run
its possible one has shorted out..

John Speake

Pin 7 LH is the output volts from the MAF. It has a very low resistance to ground only about 4 ohms...

If you check out this link
http://www.jdsporsche.com/faq.html

and scroll about 2/3rds down there are a few MAF measurements you can try.

Mike Frye

Stan, top-end was done in 9/06. All vacuum and fuel lines are new. I did check the coil wires and they look good thanks. Coils were not replaced though. I'll check out the link. john, thanks to you too. Although I think learning my car was susceptible to this may have jinxed me.

Mrmerlin

Mike from what you said does that also mean that both dampers and the FPR were replaced with new parts?
did you pull the vacuum lines to verify no fuel smell?

Mike Frye

Stan,

Sorry, I answered from my phone before. I shouldn't do that. Comprehension isn't the same when I have to scroll around the page to see all of the replies. No, you're right. The FPR is new ('87 to go with Porken chips) but the dampers are still original. I didn't pull the vacuum lines off and smell for gas. I'll check that tomorrow, thanks.

Glen McCartney

Mike, check the MAF ohms between pin 6 and 14 at the LH connector, those are the same as 3-6 on the MAF and should be around 380 ohms. When my MAF failed, the car ran super rich and wouldn't idle.

Mike Frye

Glen,

Thanks! That's what I was looking for. For some reason when I read the LH plug diagram I thought 6-7 was the ones I needed.

Like I said, I'm sure the MAF could benefit from a rebuild. I'd just like to confirm that that's the cause of these issues if I could.

Also, in reading through John Speake's website I see that I can just unplug the MAF and see if it runs better. I didn't try that either.

Pretty cold outside the last few days and my garage is occupied by my boat engine right now so it may be a few days before I get back into it.

Thanks for all the replies, will post results as they happen...

TheClairvoyant

Mike,

I've got a rebuilt MAF I haven't gotten around to installing yet. Want to swap it in to try it out?

Tom

Mike Frye

Hey Tom,

How's it going?

That's a really great offer and I may take you up on it. Let me do these checks that have been suggested and see where it leads me. I'm going to be heading up to Boston on Friday for a few days so if I can't check it tomorrow it will have to wait until after the weekend.

Can I get back to you after the weekend? (and thanks again!)

TheClairvoyant

Hey Mike,

You're welcome.

After the weekend is fine. I've had the MAF for months now and have procrastinated putting it in along with other odds and ends

No big rush....when you need it, just get in touch.

Mike Frye

Thanks Tom, much appreciated.