bad voltage regulator cause a misfire?

[stinkydogfilms]

Hello,
I'm still trying to track down my misfire in the 91 GM. The misfire is continuous, except when using very light throttle. If I turn the ac on or the headlights the misfire is a lot worse. Any clue to the misfire? All of vacuum hoses have been replaced, the intake has been gasket sealed down, ALL sensors except the DS O2 sensor has been replaced with new. The DS O2 sensor wires are not connected to anything. This has been a long on going project trying to track down the misfire the last few months. Plugs, fuel injectors, dizzy cap, dis rotor, plug wires replaced new. The coil is 6 months old, a MSD Flame thrower model. I'm going to replace the coil again today, and wait for the code scanner to arrive next week to see what it says. The cheap code reader I have does not read anything anymore.

Could the valve train cause this? I hear no noise or blow oil/smoke.
Could any of the relay switches cause the misfire? I have replaced the fuel pump relay a few times when it would idle like crap and that cleared it up.
I did a FPR test and the numbers were within spec.

Thank you,
Mike

[johnunit]

If they're <40 bucks like they are for 351w's I'd give the voltage regulator a try. It fixed similar symptoms for me.

[stinkydogfilms]

If they're <40 bucks like they are for 351w's I'd give the voltage regulator a try. It fixed similar symptoms for me.

This one is internal built into the alternator. It was an Auto Zone alternator that was removed and tested a month later.
Don't know if the AZ test the V. regulator or only the alternator. I think only the alternator was tested.

I thank you John..

Mike

[sly]

the AZ test bench only tests operational functions of the alternator (which includes the voltage regulator). It will miss off-state draw that will kill a battery in short order. To test for this, you need a "clamp meter" that clamps around the wire and measures current inductively or use an ammeter in series with the charge cable when the car is off. If there's ANY current on the charge cable when the car is off, the alternator is bad. This is how the rectifier bridge fails sometimes. It will function normally when the car is running though, so can be tested good by those bench testers.

[gadget73]

Its possible. If you can connect a voltmeter to something in the car to monitor voltage while driving, that would help. Bad grounds between engine and battery, and battery and body can cause this too. It would be worth cleaning the area where the alternator mounts to it's brackets too, since ground goes through those brackets to the engine. Honestly, that stock 65a alternator sucks though, and its entirely possible to be weak. I've had them lose rectifiers and barely function before. The tester at Advance caught that failure. I knew something was wrong with it, and the alternator was a lifetime. They tested it, the diode fail light came on, and a new one came out of the box for me.

[stinkydogfilms]

I got the scanner in and it reads

code 34, code 73
and code 91

So
34 KOER
1. EGR valve not opening properly
2. Insufficient EGR flow or EVP voltage high
(SONIC) or PFE sensor voltage out of specification

73 KOER
1. Insufficient throttle position change
2. Throttle Position Sensor Position fault/insufficient range.

91 KOER
1. Shift solenoid 1 (SS1) circuit failure
2. HEGO (HO2S) sensor voltage low/system lean
3. HEGO (HO2S) sensor signal out of range/always lean

I also did a cylinder balance test and it came out successful and OK.


HELP!
What is and where is the shift solenoid? I have an AOD.
How do I adjust the TPS?

EGR is new
EGR sensor is new
TPS is new
PS O2 sensor is new.
DS O2 sensor is NOT hooked up.

Thank you,
BTW the scanner is an INNOVA 31703 model.
I bought it lightly used cause they are not cheap.

My THANKS again,
Mike

[sly]

check the EGR solenoid for the EGR valve issue.

73 is from not hitting the throttle at the right time during the test.

91 is actually option 2 or 3 as 1 is not applicable. This probably means you have a massive vacuum leak somewhere (making everything so lean that the injectors can't compensate) or the oxygen sensor is bad or the exhaust manifold is cracked or the down pipe is loose and not sealing to the manifold. Check your vacuum lines for cracks, open ends, etc.

[slack]

Why isn't the DS O2 sensor hooked up? Maybe that's messing with the air/fuel ratio?

Link to archived page of oldfuelinjection.com about the sensor: https://web.archive.org/web/20120121...index.php?p=31

[sly]

I missed that... the oxygen sensor needs to be hooked up or it'll run stupid. If the DS O2 is bad, replace it.

[gadget73]

That will also give you the code.

and yeah, no shift solenoid. Some codes were recycled on different models. There are a maximum of 80 possible codes, so sometimes the meanings were changed with different equipment.

[stinkydogfilms]

Gadget73 and Sly you guys still bat 100% on fixing my car. Gadget73 it WAS the TFI module. Yesterday for the crap of it I put an old TFI module on and the car ran great. The smoothest it has been in months. I got about 2 happy miles from the house and it died and refused to start back up at the stop light in the middle of the right turn lane. I called AAA as a cop turned the corner. Cop didn't come back. A neighbor pulled up at the light and pushed me a few blocks to a side street. AAA showed up and was wondering why I was smiling. Because I now knew it was the TFI as Gadget said. After AAA got me home I put the shitty TFI module on and it started up and ran like crap. Now I was convinced it had been a bad TFI module. Another neighbor came out and was wondering why I was happy with AAA towing me home. So I bought a TFI module and put it on this afternoon. I have driven the car in the neighborhood for about 45 minutes with many stops and got on the main street a few times so I could shift into 3rd. No missing and no cutting out of the engine. I thank you two and everybody who have offered advice. I replaced every sensor, spark plugs twice, put the stock distributor cap and stock plug wires back on. The crappy TFI was a Petronix and only a few months old. Gone are the MSD plug wires, MSD dist cap, my home made air induction and the chip by GFORCE. Hello to Motorcraft plugs, wires and distributor cap. I'm keeping the Petronix coil for now and keeping a new Motorcraft coil and 2 NOS Motorcraft TFI modules for spares as well as all of the sensors and relays I replaced. Something kept telling me it was electrical but with the TFI and PIP sensor new, I did not think the impossible was possible. I now have a pretty good tune including replacing the fuel injectors. Now to get the brake light and horn working. I saw the thread on the brake lights and will use that information. I LOVE YOU GUYS, MAN!
Many THANKS again,
Mike