Well I installed the new pressure regulator today and I am still having the same problem.
The air/fuel ratio is fine at idle and under light throttle but at anything more than about 1/4 throttle the air/fuel ratio goes extremely lean, so much so that I can't get the car over 4,000 rpm's.
I have adjusted the spring tension on the AFM and that has helped a little but now the car runs rich at idle.
Any suggestions?
fuel pump?
AFM?
DME?
thanks in advance for the help,

 

I would start with fuel pressure, and delivery volume. Pressure should be about 36 psi I think. On the delivery test take off the fuel supply line at the rail and stick it into an empty antifreeze jug and have someone else crank the car for you. The pump should deliver at least one quart of fuel in thirty seconds. Although it may pass both of the tests, it still sounds like it is a fuel pump problem.

 

was also wondering if I might have a partially blocked fuel filter? guess it could not hurt to replace it. I just hate having to lay on the garage flow in minus 30 weather.
Oh well guess that's what I get for living in upstate New York.

 

Put a voltmeter on the air-flow meter input to the DME (pin#7, green/red-stripe wire) and measure the voltage when it goes lean at 1/4-throttle and 4000rpm. This will at least tell us if the AFM is outputing the correct signal to the DME.

 

I'll try that in the morning it's too damn cold out now to do it.

 

I measured the voltage from the afm to the dme and it looks good. The voltage tracks linearly all the way from idle to full throttle. The voltage from the AFM looks good at 4K rpm though the voltage from the o2 sensor drops to under .2 volts.
I unhooked the o2 sensor from the DME and it made the problem even worse. If I give the car any gas at all the voltage immediately drops to around .2 volts.
One thing I have noticed the last couple of days is that if I start the car up and start driving it before it warms up the ARM1 will stay at the 1st green even if I give it full gas. As soon as the car warms up though, less than 2 minutes, the problem returns.
I am going to disconect the temp sensor and see what happens.
Any new ideas? This problem is driving me crazy!

 

Now I am really starting to think this is a DME problem. I just went out and started the car. I let it warm up for a couple of minutes and then unplugged the connector to the dme temp sensor and the engine immediately died. Tried to start it back up but as long as the temp sensor is disconnected the car will not start.
Is this normal?

 

Hmmm,

I think the '85.5+ AFM should put out a logrithmic voltage curve? Goes up quickly then slows down?

Do you mean the engine-temp sensor or the air-temp sensor? The DME uses both of these.

 

I am really starting to believe the problem is with the AFM.
The temp sensor I was talking about is the engine temp sensor.
Is there any way of testing the temp sensor in the DME?
I think I may just start looking for a used AFM. If it does not fix the problem at least I can sell on e-bay for close to what i paid for it.

 

If anyone has an AFM for sale let me know. I am going to replace it first and if that does not work then I guess I will try the DME.
Thanks in advance,
dfracolli@northernfcu.net

 

hook up a fuel pressure gauge and take the car for a road test, see what the fuel pressure is when the problem occurs. If AFM signal voltage is approx 5volts when the problem occurs then replacing it is unlikely to fix it. Has the problem just recently happened or has it been there ever since you modified the engine? If it's always been there you may need a custom chip, those modifications could lead to a lean midrange condition. There is a screen in the fuel tank at the pump inlet, I have seen those clog up on occasion. If your fuel filter has not been replaced for a while, it wouldn't hurt to do it anyway. Good luck Mark T.

 

Actually the problem started about a month ago when the temp. here started getting very cold. It ran great durring the spring and summer. I originally thought it was a fuel delivery problem but the car runs ok before it warms up. I agree that it would not hurt to replace the fuel filter. I just can't get excited about crawling around on the garage floor when it is -20 outside. Wish I had a fuel pressure guage to hook up.
Thanks for the input,