Sounds like a ground did not get hooked back up when the engine was out.I have seen this before when the o2 ground was not bolted back to the rear of the head.

I can look at my spare TPI wiring harness and see how many grounds it has. I'm thinking one on each head.

Mine only had 1 ground strap on the passenger side head, and I was sure to hook it back up. I can double check to make sure it didn't come loose.

but that wouldn't make since because the engine runs fine for about the first minute.

Also the coolant is coming out of the overflow tube on the radiator once the engine starts to misfire. Only a little bit comes out in a 5 minute period, maybe 1/8th of a cup. Both fans are on (purposely; I grounded one, and the a/c is unplugged on the other.)

Should I still try switching spark plugs? my spark plug boots were hot as ****. (taylor wires)

I would change the plugs . I had problems with running Bosch Platinum plugs but it was just I had to run 93 octane instead of 87 octane fuel , but that was back when 87 octane was 99cents or less a gallon .

Anybody think the cold start injector cold be causing a problem like this? Maybe stuck open or bad switch? Just my

I thought that was a possibility too, so I blocked off the 9'th injector and ordered a new custom prom with the '89 binary.

didn't fix the problem.

Do this for a test try blocking your fuel return line and see if you get better running I thing your regulator may be allowing to much fuel to return to the tank and thats why when you use the TPS to control the fuel it adds more with your throttle plates closed . Just because you have good pressure doesn't meen you have enough fuel staying in the rails .

I checked all of the grounds on the ECM pinouts A12, D1, D2, D10 and they all checked out fine.

tried new coil, didn't fix it.

I unplugged the O2 sensor, connected the battery and started the car. It didn't fix the problem and after the problem acted up I tested the O2 sensor with the voltmeter and it wasn't reading anything higher than .14v

I've heard the same. But it doesn't make sense to me, you should see a drop when you blip the throttle if that were true or some other sign. Still though I don't have a fuel flow meter to test it and blocking the fuel return line sounds like it would blow the regulator diaphragm.

With O2 disconnected measure the ECM side of the O2 harness - you should see 451 mV DC (0.45V) - this is the bias voltage that ECM is supplying. If you getting anything else trace it back to ECM harness conenctor.

0.14V indicates that you have either a cold O2 sensor or have a very lean condition. Lean condition could be due to a header leak upstream from O2 sensor.

//RF

Voltage on the ECM side of the O2 harness was all over the place, ranging from 1.v to 14.v, what I mainly saw was it jumping from 3.v to 14.v back and forth about 2 times a second.

wtf does that mean?

I cut and checked the voltage at the ECM on the purple O2 signal wire. It read .95v.
I jumped a wire from the purple pinout wire to the O2 sensor and it cured the drop-off in RPM when the pedal is held steady, also the idle hunting wasn't as harsh, but the engine was still popping while revving WOT and misfiring at idle.

the wire that I have going to O2 sensor originally is a green with black stripe, I'm sure that's the right wire, but where's the junction where it splits from purple to the green wire?

I just looked it up on alldata and it shows the wire purple all the way from the ECM to the connector at the O2. I scanned through the wiring diagrams and did not even see a green/black wire. I was going by your sig that it is a 87 L98 car.

well that's just f'n weird.
I know that's the wire that had the O2 connector attached to it. There's not even a stray purple wire anywhere in the engine bay.
and it gets even weirder. When I had the O2 wire jumpered, the old green wire was still receiving voltage.
And I drove the car for 2 days after I built it with 0 problems.

I'm going to reinstall my heated O2 sensor, jumper the purple wire and trace the green wire.

we'll see what happens.

I looked in my Haynes manual and the only green/black wire I could find is a lightgreen/black wire that on all fuel injected engines is to the IAC .

Agree - you cut a wrong wire chief! GM always used a purple wire for O2 sensor wire! At ECM you have two connectors 24 pin (A - B) and 32 Pin (C-D). Looking at 32 pin connector pin out the O2 sensor wire should be straddled by a tan wire (O2 sensor ground) at pin D6 and D8 should be open!

Green-white or sometimes green-black stripped wire (C3) is used to control IAC - which has nothing to do with O2 sensor..

Get some isopropyl alcohol and clean wires - remove dust dirt to see wire colors clearly. All connector pins are also labeled. If you wish I can post a photo of a ECM connector clearly IDing O2 sensor wire.

//RF

I've fought problems like this before. Very frustrating. Hang in there.

You mentioned your fuel rail doesn't hold pressure after you shut down the engine. Lets find out why.

Connect your fuel pressure gauge. Prime the fuel pump. When the pressure goes up to ~40 pinch the rubber fuel supply line with pliers wrapped in a rag. If the pressure holds, you're losing pressure before somewhere before the pinch, probably at the fuel pump. It also means your fuel pressure regulator, fuel injectors, and fuel rail are not leaking. If the pressure still drops either the fuel injectors, fuel pressure regulator, or fuel rail seals are leaking.

Now prime the pump again and pinch the fuel tank return line when the pressure gets to 40. If the fuel pressure still drops either your fuel injectors or fuel rail seals are leaking. If there is no visible leak, then its your fuel injectors that are leaking. If when you pinched the line the pressure hold solid, then your fuel pressure regulator is leaking back into the fuel tank.

BTW, what cam is in this car?

What have you found out so far ?

well it's hard to admit, but I hooked up the wrong wire.

apparently the weather pack connector for the O2 sensor is exactly the same as the EGR Temperature Switch wire!

I haven't finished, I still have to find the purple wire and I think this problem caused another problem. I stopped working because I was feeling sick after calling 911 for my neighbor being slammed against the pavement from her horse, and now it's raining. I'll get to it tomorrow hopefully and I still need to try crimping the fuel lines like 350iroc suggested.

who did you pay the 20.00 to or did you keep changing the question so no one could answer it? lol

haha I knew someone was going to ask that.

I'll give it to RFmaster, because if he never would have suggested checking the reference voltage I would have never found the problem, this quickly at least. So feel free to PM me your paypal address RF.

BTW, if the reference voltage is suppose to be .45v, why am I seeing .95v?
and would voltage being sent back to the EGR temp. sw. pinout by the O2 sens. fry the ECM?

I still need to find the purple wire however, I doubt it's plugged in anywhere, it might be backwards of the firewall around the transmission.

Haha, I hope you aren't serious. This is a forum where we all help eachother. We aren't professionals. I'm sure tpi90rs will help someone out big time in the future.

I do understand his motive though. I've been through these frustrating problems before.

Maybe its plugged into the egr, lol. Maybe it got burnt on the header/manifold.

Save your money TPI90RS! I do this because I enjoy a good challenge. God only knows what other problems you may uncover. However, please keep us posted, and never despair! There is still enough good will left in this world despite what media says on the daily bases...

//RF

haha well alright. I only originally offered the $20 because I've posted about the problem couple other times, and didn't get much help or any leads. But thanks guys.

I wired back up the heated O2 sensor and it's harness, now the problem with the RPM falling off is fixed, but still has a small problem.

It idles around 650rpm and rough after it warms up, it pops and misfires under medium-hard throttle. If I gradually increase RPM slowly it runs perfect. WOT blip results a couple pops, but still revs up fast.

I did what 350IROC suggested in pinching the fuel lines, It didn't matter what fuel line I pinched, it still lost pressure. When I pinched the return line the pressure would jump up (as the "pinch" was taking up volume in the fuel line) but still drain. When I pinched the supply fuel line it still drained with no jump in pressure when pinched.

There's no fuel coming out of the vacuum to the FPR, the injectors are new and there's no leaks anywhere.

after you blip the throttle the fuel pressure will jump up like normal, then come back down and fall 2 psi below it's idle psi then it will boost itself back up.

so... bad fuel pressure diaphragm?

It can be kind of tricky to pinch the fuel lines. Maybe you weren't able to pinch it quite perfectly. Maybe try it again. But if you are truly losing pressure with both tests and you don't see any visible leaks that would point towards leaking injectors. I kind of doubt it though since your injectors are new. Try the fuel line test again.

No guarantee this is your problem though. My pressure doesn't hold either. I think I have a leaking fuel pressure regulator. But frankly my car runs fine. Just starts a little hard because of no pressure. But it could certainly be giving you problems.

After the car runs a bit does it seem to get better.

I pinched the fuel lines again with a a big pair of needle nose pliers and when I pinch the return line, the pressure holds. Pulled the vacuum hose off to the regulator and absolutely no fuel comes out. can it still be the problem if it's not leaking gas?

For the first 30 seconds or so the engine runs great, no popping or lag when blipped WOT. Then it starts popping on acceleration, but once the engine has warmed up to NOT the pops are about 50% smoother.

diaphragm?

So does it still lose pressure if you pinch the supply line? If so, I'd say its your fuel pressure regulator leaking fuel back into the gas tank.

I'm not saying fixing it will make you car run right, but I'd still do it. Get rid of one more problem.

ordered new diaphragm, gets here Saturday.

diaphragm didn't fix the problem.

I had a friend turn the ignition key while I pinched the return fuel line as soon as the pump stopped and it held pressure.

I'm lost

Is there suppose to be some kind of O ring that goes around where the "foot" seats for the diaphragm?

there was no visible signs of cracks in the fuel regulator block.

When you replaced the EGR many posts ago did you also replace the Intake Plenum gaskets? Also, did you make sure that the proper torque was applied in a star pattern? Having a bad gasket on on side could cause the motor to run lean on one side and rich on the other to make up for it.

I believe the ECM bias voltage should be measureable at O2 sensor.
As a matter of fact the datalogger should see it as well, if it's not I would srart there. My 88 on tunerpro reads 456.88mv before startup.

On your data log above I only saw one cross count, after 3 minutes there should be cross counts.

hmm my fuel pressure was 48 when i checked it last.

I may be shooting in the dark here but for starters id throw those bosch plugs in the trash, and get some delco or autolites. I have a lot of problems with the bosch plugs. And by you saying that it pushes out coolant after five minutes of running that makes me think that either you have a blown head gasket or a cracked head. Once the engine reaches a higher temp the leak gets bigger and causes it to misfire. And compression from the cylinder is forced in the coolant system and pushes the coolant out the overflow. It would also give your plugs a weird color from the coolant getting on them. Im just speculating but you should give it some thought.

It should, but it did before also.

To test the new diaphragm pinch the supply line. That way you can tell if the diaphragm is holding pressure now.