Brett Jenkins

Background: Last year, while still living in a non-emissions checking state, I removed my air injection pump and plumbing and had my cats replaced with straight pipes. Now I live in Tennessee where smog is checked, so I bought a downpipe and cats and put it on last weekend. At the same time, I replaced all my injectors with rebuilt FOTE injectors. The car fired right up and ran great for a couple days. I went to get smog checked and the car started running a little rough on the way there and I failed emissions with excessive CO. I'm thinking putting the smog pump back on will help, but obviously there are other issues.

Since I have no pump to connect to the cats, I capped the port coming off the cats.

So, last night, coming back from a serendipitous dinner with some great Porsche folks traveling across I40 on their migration from NC to TX, my car started running horribly as I was cruising along in 5th, felt like it was fuel starved or missing out (new fuel pump and filter a month ago).

I got off the interstate and into a parking lot, the car would not idle on its own, dying unless i gave it a little pedal. When it would idle, it stayed very low, like 200 rpm low and hunted up and down a bit. After I got it home, I did a few things, not all at once, but all with no apparent improvement.After all changes, the car would start right up, but would die immediately. I unplugged the negative cable to reset everything. I unplugged the o2 sensor. I unplugged the temp II sensor. I checked all injector connections and the knock sensor connections. The only thing that helped, and only a little, was unplugging the MAF. That at least let it start up and keep running, but the idle hunted a lot. I plugged the MAF back in and it still started and kept running, but just as poorly. I thought maybe bad gas and since I was down to less than 1/4 tank, I filled it up with 93 octane shell gas, no improvement.

Could a bad or offline injector be causing this? One thing I noticed was that the cap I put on the air injection port on the cats was gone, must have vibrated off. Maybe that opening in the system is messing up back pressure or throwing off some system.

So, any thoughts or suggestions as to what to check?

AO

Sounds like a bad MAF.

Brett Jenkins

Should it at least be drivable with the MAF unplugged or is the MAF absolutely needed to operate at all?

John Speake

Car will idle pretty well with MAF disconnected (somewhat rich) but barely driveable o0ff idle - very much an emergency default.

Alan

Are you sure you didn't lose a whole bank - maybe an ignition final stage or coil.

check spark per cylinder.

Alan

auzivision

Might swap the fuel pump and horn relay. Do you have a way to check fuel pressure?

Brett Jenkins

The fuel pump relay just occurred to me too. I started it up earlier and something I noticed is that the hum of the fuel pump would rise and fall with the RPMs at idle. Either the idle fluctuation causing the hum to fluctuate, or the fuel pump fluctuation is causing my poor idle. Maybe the relay is cutting in and out. It's fairly new, but I do have a new spare as well. I'll go give it a try shortly.

Brett Jenkins

Update:

Replaced fuel pump relay with a new one. Same results, car would start and either die immediately or idle horribly.

Unplugged o2 sensor, thinking maybe i buggered it up during my cat re-installation, pinched or melted or something. Same result.

Unhooked battery again and let sit for a few minutes. Hooked up battery and the car started up and idled rock solid, albeit a bit high, but no idle fluctuations, no dying, no sputtering. Running like a champ. I think the high idle (1200) is probably a vac leak, so I'll chase that this weekend.

Took it for a spin around the block, no issues at all, other than hearing the exhaust leak where the air injection pump inlet on the cats needs blocked off again.

So, i think the new relay + resetting the brains did the trick. I'll go for a longer drive later and see if it stays solid. Keep your fingers crossed. :-)

James Bailey

To be accurate it is two cylinders on each bank when an ignitionissue takes place........
I am not sure that having it running O K now is a benefit as it makes the real problem far harder to find and the car potentially very unreliable. Good luck with it.

Brett Jenkins

Well, my success was short lived. Drove into town for dinner, ran fine. Went to leave, it was running worse than before. Seems to be very rich, exhaust smells awful, almost like moth ***** and a hard rev will blow black smoke.

Back to the garage I guess. I can change parts with the best of them, but I don't want to just start throwing expensive parts at it until it's fixed. But, my diagnosis skills are weak. So, a suggestion of what to check with some instructions on how to check it will be very much appreciated.

I should add, that before last weekend's maintenance the car has been very reliable. A little rough running once in a while, but never anything like this. Again, the changes were new injectors and putting a used downpipe and cats back on it.

Would it be possible for one of the injectors to have popped loose from the cylinder or fuel rail without leaking and cause this?

Could the used cats have decided to clog up after running them a few days? Would that manifest like this?

Thanks for any and all help.

Mrmerlin

AHHH I would suggest that the next time you run the car you get down and inspect the cats,
see if they are glowing red,
if so your on the verge of burning up your car,
I would pull the coil wires off and inspect them make sure the ends are clean and they are not rubbing on any parts of their run,
also pull off the vacuum lines to the FPR and both dampers and smell the lines for fuel ,
if you smell gas then you need to replace the part,
after all of the this consider swapping out the MAF or get it checked or rebuilt

Brett Jenkins

I took a look at the cats last night, they were not glowing then.

Is it possible to test the MAF on the car, or does it have to be bench-tested?

I guess it would be best to determine if it's a fueling issue, a spark issue, etc.

Is my workshop manual the best source for instructions to test each component, or are there better write-up available?

SteveG

The easiest test is to put in a known good MAF (who is close with an 88) or put yours in another car and see how it runs. Otherwise you have to send it out.

John Speake does tests and rebuilds and Electronik Repair (Rich9928p??). Roger might be able to send a loaner?

You might be able to use an '89 as well, but that is out of my range. Somebody help.

Brett Jenkins

I'll try to source a MAF to test out.

As evident by the black soot it's spewing under load, it seems to be running very rich.

I tested the FPRs and dampners and they all held vacuum.

The coils and coil wires are fairly new. I pulled each coil wire and checked and reseated them firmly.

Would improperly seated injectors cause this? I noticed a couple of them are not seated as far down as others, causing a vacuum leak maybe?

I'll do a few other tests as time allows.

John Speake

Louie Ott in OR stocks my MAFs. He can also test your MAF for a fee.