[nomname]

Desperate please help.
I have a 1988 5.0 gt mustang stock that is just killing me on this.

When it runs good it is very good. Good and strong just the way is should.

But, when it runs bad it will hardly start or runs so rich it's black and sooty out the tail. The problem come every morning after sitting all night but after a time of trying to run it and messing with it, it will run great again, but then again back to very rich in the morning.

I've changed:
O2 sensors
MAF Sensor
TPS Sensor
IAC
Plugs
wires
distributor cap and all.
New gas
Cleaned throttle body and linkage

But still burns very rich and poor.

But it seems once warmed up and then sits for a few it will run great.


Any suggestions?

Thank you.

[428CJ]

You could try replacing the ECT, my car ran super rich until I replaced that sensor.

[fogged306]

Is it a speed density car or a MAF car? If it's SD, check for vacuum leaks. Also check for codes. You're flying blind unless you see if there's any codes stored that can lead you to something. How to check for codes

[nomname]

It's a MAF car. I ran codes but every time i replace what is says is low voltage or bad reading it never runs better and I'm just racking up costs. So... I'm not trusting codes at this time.

I'm still getting bad voltage for:
MAF
ECT

I've checked for vacuum links but found none. It's very odd and I'm out of ideas except keep replacing things. To date I'm over $500 in parts and about 40 to 60 hours of time with no significant change in outcome. And now it will not stay running. Also when it was running nice I filled it up and after 70 miles and some idle time, I'm down to 1/8 of a thank. So very very rich. Black, black, black out the tail pipes. Just popping and sputtering.

I've changed:
O2 sensors
MAF Sensor
TPS Sensor
IAC
Plugs
wires
distributor cap and all.
New gas
Cleaned throttle body and linkage

But still burns very rich and poor.

Had to have the gas peddle all the way down to keep it running last night and this morning. So it's back to where it was before replacing all those parts. NO wost.

But again when what ever it is starts working and the car runs, it is a dream. It has lots of power and very responsive. But then back to bad in morning.

Also I've had this car since 1991 so I know it's history.

Codes this morning
Ignition on engine off:
11
10
56

Could not get it to run enough to check codes running.

what a ....

I have an ugly 1994 dodge caravan that will not die no mater what I do to neglect it and she always treats me well.

Mustang I only drive in the summer and spend about $2000 every year treating it right and buying it pretty thing like new paint, new top, new parts, new tired, nice sound system and so fort and it only teases me and asks for more.

As an upholsterer, I had new upholstery all picked out too for this year. A really nice burgundy velvet for the Seats, and door panels. I was even going to upholster the counsel in a matching Naugahyde with top sticking. I talked to a local embroider shop about the mustang emblem for the seat backs. But no. She is only a tease. My love is fading.

Maybe it's time for a new girl.

Please help before it's to late.

[428CJ]

I know where your coming from. With my car I loved it from the day I got it, but over time, with problem after problem, I lost all motivation to do anything to it. Now I'am thinking of getting a new fox aswell.

[FastStang91Lx]

Replace ECT and ACT. They are cheap!!! And more than likely one of them is your issue.

[nomname]

As advised here and by a trusted mechanic new ect and act. Still no go.

Its a damp rainy day maybe something about that, But will not start at all now. Turns over but will not start. I'm getting a spark. Sounds like it is starving for fuel to me.

I was also advised to look at the fuel pressure gauge on the fuel rail, or such.

Any suggestions from here?

Thank you.

[nomname]

Monday Update:
Replaced fuel pressure gauge on fuel rail. Pretty big job. You can see it but the screws face down so fuel rail has to come off.
Did not run any better. It turns over fine but sounds like it's going to start but just turns over and want quite ketch.

So I:
Cleaned spark plugs again
Checked spark again started focusing on spark.

Got the car to start last night but run pretty bad still and very hot out the tail pipes, but not as much black smoke.

Getting code saying EGR not opening correctly. I had cleaned it and checked vacuum and it's fine.

Next I'm checking ignition module. Starting to think it is a spark problem now. And will replace spark plugs. These only have a few hundred miles on them but... who knows.

Also checked firing order it was fine. Yes new wires, cap .

So, I got it to start again but not drivable by any means.


Here in Seattle Summer only last a month in a good year then it's back to 395 more days of rain. So any help would be appreciated. Summer start tomorrow so we will have sun from July 5th till August 15th. Please help before I have to put the Convertible back for the winter.

Thank you

[fogged306]

Pull your ECU and open up the case. Take a look for any blown traces or capacitors that have burst at the bottom. You'll see a little puddle of black goo under them if they are shot. If you've replaced the MAF and are still getting a code for the MAF sensor then I have to believe you have either a bad computer or a bad wire somewhere. I would also check/replace the grounds for the block, battery, and computer.

Was it a california MAF car or was this an original speed density car that someone changed over to MAF? The swap wiring/plugs could also be faulty somewhere.

[nomname]

fogged306
It's a California car with a stock MAF.

The weather today is warmer and dryer and with out doing anything more to the car, It started right up, and it was running better with no smoke But engine light stays on and it ideals ruff. When put in to gear (automatic) and give it some gas, it hesitates and then jumps into motion.

Codes now when running:
56- Mass Air voltage high and transmission sensor fail
98- Hard Fault.

I planning next to change all the vacuum lines next and I'll open up the ECU as Prescribed by fogged306

Thank you.

[nomname]

Here is an update if to an advantage to anyone with an 1988 mustang Gt 5.0 or about that time with a similar problem as above.


I had an old timer with 50+ years in auto mechanics have a look. He heard vacuum problems. So to the pcv valve he went, and under the pcv valve is a puck like wire screen down inside the intake manifold, aka a Breather Filter.

It was completely plugged with carbon. Off to Auto Zone and it looks like we or he "may" have solved the problem. I am now running a carbon cleaner called Sea Foam though the vacuum system via a vacuum line as recommended by the kindly old gentlemen mechanic.

It seems to be doing better. If not further post then success.

Thank you to everyone who gave suggestions and encourage me though this difficulty.

PS. The last 2 days were nice and sunny. It's now raining here in Seattle where it rains 432 days a year.

Mother nature does have a sense of humor.

PPS. If you never have then do check your Breather Filter when you get a chance if you never have. I was shocked at how clogged up mine was. I for one never new it was there.

Best