I got my car back on the road yesterday after sitting for a while. I went for a quick ten minute test drive, everything was fine. When I got back home, I let it sit for about an hour and went to start it up again, and it's only wanting to run as long as I keep my foot on the gas. It did that a few months ago and that's when I tore it down again trying to find the problem. Soon as I take my foot off the gas, it dies.
Yesterday I did notice though that it was having problems staying running when I put the valve covers back on. I started it up and it would only idle at about 400rpm. Something told me to take a breather off and when I did, it idled at 700 like it's supposed to. That's when I went for the test drive.
This morning, I decided to tinker around with it and have found a couple things. When I tested the TPS, it was reading over 4 volts with the throttle body closed. With it wide open, it's reading about 1.5 volts. I even swapped out that TPS with my spare and it's doing the same thing. I'm getting no TPS codes. The only code I get is the 34 for the MAF, but everything tested there is fine, it just keeps throwing that code for some reason.
I've got fire on each cylinder. Fuel's going to each one, got good fuel pressure too. There's air getting in the intake, the throttle body's slightly open from the adjustment screw. I just don't get it.
The last time it was running, earlier this year, I replaced the spark controller (it died) and the MAF and fuel pump relays for the hell of it. It was running really bad and smelled like rotten eggs and would only move if I held the pedal to the floor.
Would anyone like to venture a guess as to what's going on?

 

The rotten egg smell is coming from your catalytic converter. It is probably going bad.

The Trickster!!!!!!!!!!!!!!

 

Nope, brand new.

 

did you look at your pvc valve? you said idle was better with breather off. which breather you talking about? on valve cover?

also check you egr selnoid make sure the wires are on it. may have come off when you took off the valve cover. egr s is on pass side rear of intake should have wires and on small vac tube to egr valve.


rotten egg smell is cat but could be from sitting so long that should go away.

 

Ok,

Well I guess that shoots the heck out of that theory about the cat. Next thing is your TPS is only supposed to read about .54 volts closed and close to 5 volts at wide open throttle. So if was reading over 4 volts at closed and about 1.5 volts at wide open throttle, I would say that you have a serious problem with either the tps, throttle adjustment, or the ecm. Also check the air duct for loosenes, cracks or holes. You will also get a code 34 if you have rough, unstable, or incorrect idle.

The Trickster!!!!!!!!!!

 

I got the TPS worked out.

While the car was down, I replaced the IAC. I've tried to erset the minimum air, but it's not even running with the AIC disconnected, so I can't reset it.

Tell you what, I'm about at wit's end with this car. I've owned it two years and it's only run for four months.

 

How are you measuring the TPS voltage? Sounds like you are measuring the voltage on the wrong wire.

Check the MAF connector real close. The female pins inside can spread and can also move up inside the connector so they don't fully engage the male pins on the MAF.
I don't have the schematic handy since I'm at work, but the pin on the maf connector that connects to the ECM should have ~5 volts with connector disconnected from MAF with Key on, eng off. When connected to MAF the same pin should be less than 1 volt with key on, eng off.
Also check the MAF relays.

Check eng-to-body grounds too.

 

I was.

MAF relays are new. It actually never threw a MAF code until a few months after I bought the car when I took the MAF screens out. This code has been popping up ever since, but every test I can run on it says the MAF is fine.
I'll check those grounds tomorrow. I'm about to give up on it though and get back to building the other motor. I'm hunting for a stock replacement crank.

 

Just glad you didn't ask how I knew you were on the wrong TPS wire!

Looking at an 87 GTA schematic now. The 5v wire I mentioned previously is dark green and connects to pin#3 (center wire) on the MAF connector. The other end connects to pin B12 at the ECM.
The ECM supplies 5 volts to the MAF. The MAFs job is to pull the voltage down. The less air thru the MAF, the more it pulls down the voltage. If there's a bad or intermittently bad connection, the MAF can't pull the voltage down as far as it should. The ECM will see a higher voltage, assume there's more air coming in than actual, and increase the inj pulse width making eng run really rich.

On my EPROM (stock 87 GTA) there's a constant called MAF diag error threshold (or something like that) that was set to 45. If the ECM sees 45 or more g/sec from the MAF with TPS at idle, it will set a MAF error code.

 

Oh yeah, the rotten egg smell is from running too rich.
Pull a couple of plugs. Bet they are a dull black color (fuel fouled).

 

Oh, the egg smell has long since passed. Fixed that a long time ago.
I'll check that MAF reading when I get home tonight.

 

Okay, the MAF plug is reading 5 volts and when I plug it in, I'm getting 2.5 volts.
I've double checked all the grounds too. Any other ideas?

Forgot to mention. I found this little test while searching this board. I hooked up my timing light to #1 and cranked the car. It wasn't even lighting up the light when I pulled the trigger. Then, I unplugged #1 and set it on the frame and it wasn't arcing when I cranked either.
Bad ignition module? It was replaced two years ago when my friend rebuilt my distributor, but I remember I bought the cheapy brand because I didn't have much money. Could it be a sign that it was dying because sometimes the car would start and sometimes it wouldn't?

 

The MAF is not pulling the 5 volts down far enough.
The ECM thinks the air flow is abt 125 g/sec.
At Idle, it should be abt 7-10 g/sec.

The MAF connector pins are labeled as:
Pin A= Chassis ground.
Pin B= Ground thru the ECM.
Pin C= we already covered, 5V line from the ECM.
Pin D= Burn-off connection
Pin E= 12 volts

Verify 12 V at pin E using pins A and B for ground.

Verify that pins A and B have a low resistance to battery ground.
If they do not have a good ground, the MAF can't pull the 5 volts down like it should. If grounds are good, and the 5 volts is only being pulled down to 2.5 volts, the MAF is probably bad.

 

The ign sounds like it has problems too.
See if there is spark coming from the coil.

 

What color is pin A so I know where to start?

The coil's firing away, but I'm getting no spark to any of the plugs. Pretty much narrows it down to the ignition module. Funny though, how one minute it's giving me spark and the next it's not.

 

I've replaced the ignition module and it's still getting no fire from the dizzy. I checked for continuity in the wire going from the coil to the ignition module and it's fine. I checked the pink wire with the key on and it's getting 11.7 volts. The dizzy's spinning, so what does that leave me with?

 

Have you looked at the distributor hei module and pick-up coil or the wiring for them? You mentioned a problem after putting on the valve covers, did you pinch a wire maybe? Just a thought!!

The Trickster!!!!!!!!!!!!!

 

Trickster, I think I got it narrowed down.
I took the cap back off and tested the pickup coil leads and got no continuity and no continuity between the leads and ground, which is how it's supposed to be. I did find, however, that one of the leads had been pushed down into the connector, so I figured that was my problem. Put the cap back on, wouldn't start again.
I decided to check the coil for resistance and I think it's pretty much toast. I did all three tests as shown in my Haynes manual and I was reading 0 ohms on each. On test one, it's supposed to read near zero. On two, it's supposed to read very high, and on three, it's supposed to read infinite. Funny though, it's sending fire through the coil wire to the dizzy, but I guess it's just not strong enough to go any farther down the line.
Looks like I'll be buying a new coil tomorrow.

 

redrummer,

You have e-mail coming!!!!!!!!!

The Trickster!!!!!!!!!!!

 

On the MAF connector;
Pin A is black-white
B is black
C is dark green
D is dark blue
E is red

If the coil is firing, the pick-up coil, module, and ign coil are probably OK.
Rotor, coil wire, dist cap or plug wires may be bad.
Remove and inspect the rotor and cap. Look for obvious problems.
Burned or damaged contacts, moisture,etc.
Using a bright light, look for very thin black lines inside dist cap (called carbon tracking).

 

ZZ, it's the coil. I ordered a new MSD last night.
Thanks for the info though, I'll check that MAF tonight.

I'm getting tired of testing stuff. On the bright side, at least I know everything's good.