1992 5.0 Mustang GT - bad jerks & idle

[bobbywalter]

thats the o2 sensor pcm ground, should be orange and go to pin 49.

Pinned the green & black TPS, and there is no voltage sweep across the board.

do you mean no voltage spikes? because if theres no sweep the tps is toast.


still seems like a bad pip signal (when i say pip i mean hall effect sensor) bad pcm power/ground or sticky/leaking egr from the description to me.

The tach jumps from 0 rpm to 1200 rpm all the time, yet randomly.

really seems indicative of the pip or bad ground. te connections at the coil may be loose etc.

this assumes fuel pressure is correct and vacuum leaks are tested and ruled out. is there a resistor in the idm circuit going to pin 4?

 

[AgPete139]

In my entire 15 years of owning my 89 GT I have had the check engine light come on twice (once for EGR position sensor, the other for a bad O2 sensor). It's really an awesome system, just bad at telling you what's wrong when something is wrong.

The check engine light blinks, but that's normal even when nothing is wrong. I still have no codes.

I agree with your friend, the O2 sensor wouldn't do this on an EEC-IV car.

Anyway, something you wrote caught my eye. You say the tach jumps from 0 rpm to 1800 rpm. Is the motor revving with it?

Yes, they both drop in RPM at about the same time. It hard to tell since it revs so randomly; the idle alone is barely a 900 rpm anymore, if at all.

If not, I'm pointing the finger at a bad ground or a bum ignition coil.

I now replaced the ignition coil with a new Borg Warner one.

Have you ever had the heads off of the car?

No.

The reason I ask is there is a very crucial ground wire that is connected on the back (by the firewall) of the drivers side head. This grounds the entire engine harness if I remember correctly.

It is a wide, braided ground strap with a brass ring connected to the 8mm green firewall bolt by clutch cable. This, and 3 grounds on the driver fender were sanded down and connected. Cleaned battery terminals, connectors, cut terminal wires back.

If this has a bad connection or not hooked up, I think this is your issue. My wire is orange in color with a brass ring connector. It is located pretty close to the emissions pipe that connects to both heads. The other reason I think this is a pretty good possibility is the SPOUT not doing any changes plugged vs. not plugged in.

I never saw an orange wire. Didn't see anything close to the emissions pipe. Am I looking for something different than the braided strap?

The SPOUT connector...how should I retest that for fault? I am beginning to lean toward this as a problem now...

However, your alternator could also be playing a role, but not likely. I bought a bad one from Autozone years ago that made my car wig out. My gauge was bouncing though. They gave me a replacement that had bad bearings in it and it seized, so I bought a used one which worked much better for about 6 years. Last August I replaced that with a 140 amp off of a 2001 V6. This was in part to Ford's terrible connector they used on the stock alternator. Be sure to check your harness (the one that has the 2 charge wires which are black with an orange stripe) for being burnt. If yours is burnt let me know, I may have one in my parts collection.

Yea, and my lights/accessories would also dim. It's not the alternator.

I doubt you'll find it to be the pump, it flat won't run at all when that dies. What you've said convinces me it's electrical.

I really don't want to drop the tank just to check for a corroded wire.

******Now that I'm thinking about it, that ground wire for the engine harness MAY be connected with one of the bolts for the emissions pipe. So if that pipe has been messed with, that's a possibility as well. I don't have the pipe anymore because I have GT-40P heads or I would go look for you.******

I will check again tomorrow for this notorious OJ wire with exhaust pipe. I will check behind the #4 & #8 cylinders.



Peter

 

[AgPete139]

you can leave all the emmissions componants in place and just turn them off with the Q/H....you can completely mod the system to perfection....it is a custom ecu at that point.....not impressing anybody, just dialing in the car better for your application verse some generic meet all oem tune.

I don't have the $500 for a Q/H setup. And this is definitely interesting. Looked at the Moates website. Will look into this as a possibility for my next mustang...

a fuel pump will certainly lay down and cause erratic behaviour exactly as described.....especially if the connector is corroded.

I am going to try and rule out electrical in the engine bay first before I siphon and drop the tank. A corroded wire is sitll a possibility. The pump seems to be delivering with the new fuel filter. Shane and you both have different views on the fuel pump. I still think I should drop the tank and check. This daily driver is a big inconvenience now...

i do agree that between a bad ground or pip is highly likely. but a sticky egr has potential as well. may just have some capacitor leakage starting on the board or some other damage within the old ass ecm.

I have completely disconnected the EGR vacuum hose & EGR position sensor, and even though the valve never moved, it still idles odd. If the engine will run fine with emissions & AIR system disconnected, wouldn't the car compensate and idle correctly in this case?

i know i would need to have it and drive it to find out what the issue could be, and that if i could find it.

Thanks for your advice, Bobby. Everything is helping me understand this car quicker and better every time I log on.

Peter

 

[AgPete139]

Hey AgPete139, I have some information on your car that may be helpful. There is a guy with the handle TMOSS on www.allfordmustangs.com who has gone through and done pinouts on ECU's for Mustangs.

Your 92 ECU specifically is at: http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Lots of other info here, like alternator wiring: http://www.veryuseful.com/mustang/tech/engine/

This is the ground wire I think you should is #19 in this pic: http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

You may want to join over there and talk to TMOSS, he is a genius.

Let me know how it turns out!

Still looking at everything...

thats the o2 sensor pcm ground, should be orange and go to pin 49.




do you mean no voltage spikes? because if theres no sweep the tps is toast.

I switched out the TPS with a new one. I drove it, made no difference. Returned the $75 part. I don't see voltage spikes when I'm plugged into the TPS wires. Voltage seems steady at steady, held partial throttles. The tachometer dips in RPM. I guess "sweep" is an incorrect term use, since it's not fully hitting all parts of the tach.


still seems like a bad pip signal (when i say pip i mean hall effect sensor) bad pcm power/ground or sticky/leaking egr from the description to me.

I still gotta find someone with a known working EGR & hall effect sensor. It's $4, maybe I'll just f***ing replace that HES, too. Gonna recheck the PCM ground and the OJ wire.

The MAF sensor is NOT to blame. Switched it out (only available as an entire assembly with the metal housing) with a new one, no change. Returned part.





really seems indicative of the pip or bad ground. te connections at the coil may be loose etc.

There is only the coil itself, and the 2-wired plug.

this assumes fuel pressure is correct and vacuum leaks are tested and ruled out. is there a resistor in the idm circuit going to pin 4?

A vacuum gauge is going to be installed on that d**m vacuum tree tomorrow. Both mechanics don't have vacuum pumps (I kind of find that hard to believe). One of them is really trustworthy and a family friend for over a decade, and he has completely given up on my car as well.

Ignition diagnostic monitor? Pin 4? I don't know which you are referring. I'm sorry.

http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif





P.S. The wiring harness JPG was cool & useful. I will try and check more of those connections tomorrow as well.


Thanks guys for staying patient with me. This is frustrating...

Peter

 

[shane96ranger]

I don't feel it's the pump because a pump won't make your idle surge. A bad pump will make the car die. It may start again after it cools down, but in my experience a pump will be on or off intermittently until it inevitably fails. However, if you would like to rule out the pump (which I do think is a wise choice, I just seriously doubt this is your root cause) I had mine down and back in within an hours time to replace my sending unit last summer. I didn't even pull it all the way out. I just took the inlet tube bolt out and supported the pump with a jack on the drivers side while I took out the two strap bolts. Once those 3 bolts are out, just lower the jack slowly and work it back and forth on to slide the tank down the inlet tube. Just be sure to put a coating of clean motor oil on the inlet tube when you slide it back on.

Mine is an 89, so yours being 3 years newer may have a different ground strap. I'm almost certain mine was orange, I'll check tomorrow. I thought my braided strap went to the firewall. I'm working off of memory right now, I haven't driven it since October - it's my summer car.

And forgive my ignorance Bobby, but what is PIP? I'm not familiar with that term.

As far as the SPOUT connector is concerned, didn't you say you have some friends with Mustangs? I'd borrow one of theirs and try it out. Forgive me if you already know this, but the SPOUT is like vacuum advance on older cars. By the way, what is your timing set at? It should be in the 9 to 14 BTDC range. I run mine at 13btdc.


One more addition to my post.....I would really consider joining allfordmustangs.com because there are a lot of knowledgeable people on there. It's very well ran and not a bunch of dinks on there. I guarantee you'll find a fix on there. There's a couple guys TMOSS and 89Coupe that are very well versed in the EEC-IV system. My knowledge is from experiences and my Ford book.

 

[AgPete139]

"The CMP sensor, housed inside the distributor, responds to a rotating metallic shutter mounted on the distributor shaft. This rotating shutter produces a digital Profile Ignition Pick-up (PIP) signal, which is used by the PCM and TFI to provide base timing information, determine engine speed (rpm) and crankshaft position. The distributor shaft rotates at one-half crankshaft speed, therefore the shutter rotates once for every two crankshaft revolutions."

http://www.therangerstation.com/tech_library/TFI_Diagnostic.html

Peter

 

[shane96ranger]

OK, so the PIP is the pick up coil then?

 

[jaymegriffiths]

I don't feel it's the pump because a pump won't make your idle surge. A bad pump will make the car die. It may start again after it cools down, but in my experience a pump will be on or off intermittently until it inevitably fails. However, if you would like to rule out the pump (which I do think is a wise choice, I just seriously doubt this is your root cause) I had mine down and back in within an hours time to replace my sending unit last summer. I didn't even pull it all the way out. I just took the inlet tube bolt out and supported the pump with a jack on the drivers side while I took out the two strap bolts. Once those 3 bolts are out, just lower the jack slowly and work it back and forth on to slide the tank down the inlet tube. Just be sure to put a coating of clean motor oil on the inlet tube when you slide it back on.

Mine is an 89, so yours being 3 years newer may have a different ground strap. I'm almost certain mine was orange, I'll check tomorrow. I thought my braided strap went to the firewall. I'm working off of memory right now, I haven't driven it since October - it's my summer car.

And forgive my ignorance Bobby, but what is PIP? I'm not familiar with that term.

As far as the SPOUT connector is concerned, didn't you say you have some friends with Mustangs? I'd borrow one of theirs and try it out. Forgive me if you already know this, but the SPOUT is like vacuum advance on older cars. By the way, what is your timing set at? It should be in the 9 to 14 BTDC range. I run mine at 13btdc.


One more addition to my post.....I would really consider joining allfordmustangs.com because there are a lot of knowledgeable people on there. It's very well ran and not a bunch of dinks on there. I guarantee you'll find a fix on there. There's a couple guys TMOSS and 89Coupe that are very well versed in the EEC-IV system. My knowledge is from experiences and my Ford book.

could not the fuel pump be weak because of a bad ground or connection causing the fuel pressure to dip cause the erratic idle?

 

[AgPete139]

SOLUTION FOUND:​

Sorry for the long delay. Like many threads on here, once a solution is found, the thread is ignored and nobody else becomes aware of the outcome.


It ended up partially being the Ignition Module (Ford is a must, autoparts aftermarket did not last and had short lives) and the entire distributor. When you turn the distributor gear, the pickup wobbles inside the distributor housing like crazy, and was barely making contact with the pick-up while at other times it was grinding too much, causing excessive friction and horrible, irregular idling.

I had assumed my distributor was fine with only 100K original miles, and I had switched out my distributor cap+rotor, wires, and Ignition Module (though non OEM). I was close (in the general electrical realm)...it just didn't occur to me that the entire distributor was capable of wobbling.

It was suggested earlier in this thread that I switch distributors, but I did not have another good, entire distributor in my garage. Finally, I was able to use/switch it out with another distributor from a guy that lives an hour away. After removing the old distributor, the flaws became quite apparent.

I will take pics the next time I have my camera.


Lessons Learned:

• Always use an OEM, Ford Ignition Module
• The $3 crooked distributor wrench from the auto store is invaluable
• The distributor pick-up and housing can wear out
• Make sure solid contact is made w/ the ignition coil & ignition coil wire
• Become familiar with the PIP, Ignition Module, & how the electricals work, since it is very basic but very critical to understand your OBD1/OBDI Mustang or 5.0L swap.

THANK YOU JAYME, WALTER, & ESPECIALLY SHANE FOR ALL OF YOUR HELP !




Pete

 

[Dangeranger3]

Glad you got it figured out Pete