Scott, cant find in the thread where you have done anything with the AFM... never mind, saw it

OR the TPS / AFM to DME wiring harness... these things are brittle, and broken wires can cause all sorts of havoc..

have you tried wiggling the wiring harnesses while the car is running.. it sounds almost as if vibration of the engine running is causing intermittent changes in the operation... you can use a multimeter to ring out the harness, but be aware that the leads need to be LONG and the harness will need to be wiggled to ensure readings are accurate...

Another possible swap from Herbie you could do is the coil...

also, have you been able to run up the engine temp to see if this is only with a cold engine? (DME Temp sensor..)

Do you have any way to measure the AFR durring your efforts? WBO2 would work, but emmisions test locations can also measure this using a tail pipe probe... just a thought, as it would tell you if the rough running is a result of overly rich or lean...

Trying to remote trouble shoot and help with any ideas that pop into my pea brain...

 

John,

Thanks for the leads. Your thoughts are always welcome.

It could be in the wiring. I hate messing with wiring - but this does seem possible. Coil is easy to check - it's one of the few things we haven't tried.

What is the little cylinder under the intake manifold? It looks to have an electronic connector going to it and maybe some vacuum lines.

I have allowed the engine to get warm while at idle. No problems. Once the engine is revved and then throttle released, it runs like crap again.

No way to check AFR. About all we can do is throw parts at it right now.

 

I sorta have the same problem on my 85.5. Will start doing all the tests described in the post and will get back if I find anything.

Actually the first thing I will check is the AFR.

 

Found two problems: 1. The hose from the oil seperator to air boot is leaking. Upon close inspection is is cracking along its lenght. 2. The hose from the ISV to air boot leaks also and looks the same.

I used carb cleaner and after spraying these two areas the engine RPMs picked up.

Michael

 

Based on a tip from a good friend, we are now thinking it is a clogged cat. This had been in the back of my mind as a possibility. We will be checking this over the upcoming weekend.

 

It's not the cat. Diconnected the exhaust at the headers and dropped it out of the way enough to permit little, to no, flow though the rest of the system.

Swapped another fuel pump in, again!
Again, it didn't matter.

Swapped the check valve for the purg tank. No change.

Have messed with the connector on the idle control valve. Not a strong suspect.

I am beginning to think there might be a mechanical problem. Maybe a broken valve spring? Does not make sense with the good compression numbers.

When it idles - everything seems so normal. This is becoming very frustrating.

 

You probably have a break in the wire harness under the boot on the AFM plug.

AFM voltage at idle is fine, but as soon as it has to do any sort of metering of air, it is being confused. The problem is AFM or wiring related.

The idle control valve wont cause this, a vaccuum leak wont cause this as if it were big enough to make the engine run rough, it would be big enough to kill the engine at idle. There is a chance it could be spark or fuel related, but since you checked those, rule that out.

 

Did you ever check your cylinder temps to see if there is a faulty spark or injector? I'm still thinking injector, but could be a sticky valve. Try running some Marvel Mystery Oil, or automatic transmission fluid in the oil?

 

AFM was swapped from Herbie to Penelope. The engine ran crappy still. Both work fine in Herbie. Have messed with the wiring and the harnesses in the engine compartment. No changes. It still could be wiring - but it is not in a readily accessible location, if it is.

I have not totally ruled out a fuel problem. It really is reacting as though it is fuel related. It's just not obvious.

 

I did check temps. At first, it looked as though #3 was lower than the other cylinders. I think it was due to bad placement of the IR beam. The little laser has burned out in my cheap temp gun.

I switched injectors, plug wires and spark plugs to #3. Still no change. With a little better aim of the temp gun, I got readings in-line with those of the other cylinders.

Regarding the sticking valve idea. I'm not sure how a sticking valve would work OK at idle and then become sticky at higher revs. Not that anything else has made any sense, so far...

 

Fuel pump check valve?

944.608.951.01

 

Nope. Have swapped between the two cars. Both work fine in Herbie.

 

So, it runs OK at idle and with the first rev up runs OK, and then starts stumbling after returning to idle? You checked fuel pressure, have you checked the flow rate of the fuel pump also?

Have you tried disconnecting the O2 sensor and running it?

 

Scott,

I'm with Rock on this one. I think it's got to be the wiring from the AFM to the DME.

Have a look at this page, especially the bottom most pic:

http://www.frwilk.com/the944/afm.htm

You can do the following checks at the AFM connector end. Check for good ground through the harness at pin 6 (no or very low resistance from pin 6 at the AFM connector to ground. I'm not 100% sure it should be direct to chassis ground though); voltage between pin 9 and ground (check to pin 6 and chassis ground) should show constant voltage around 5v (regulated supply from the DME, so the ignition needs to be on.)

Pin 7 is the signal going back; it should vary as the barn door opens. There's no easy way to test integrity of that wire that at the AFM connector end, you'll have to check it at the DME connector end. Thankfully, the pin numbers are the same. Pin 7 on the DME connector is the same pin 7 on the AFM connector. There's a diagram here:

http://www.frwilk.com/the944/connector.htm

If you remember, I suggested an analog volt meter or oscilloscope would be needed to test this. You need to supply voltage to pin 9 and ground to pin 6 ( like by hooking up a 9 volt battery. read voltage between pin 7 and 6 and watch it go up steadily and smoothly as the barn door is opened.

 

John,

That's what we will be looking at this weekend.

If that is not it - I'm seriously thinking of dropping it back at Jen's place and getting back to work on my stuff.

So you never said how long you plan to stay in Seattle. Long term?