Car running poorly. Ideas?

[ratio411]

1988 5.0/AOD/4.10
MAF system

About 2 weeks ago the car started running sub-par.
It started out barely noticable, but has gotten progressively worse.

It has been several months since it had basic tuning done, so we:
Changed plugs, wires, cap, and rotor.
Cleaned the K&N and MAF.
No CEL
Car had new o2 sensors less than a year ago, and they look great.
MAF is only a few months old, and looks great, but we did shoot it with cleaner.
Injectors are less than a year old.

The car runs smoothly at times, right when it is first started, and after it is warmed up.

However, shortly after start up until hot it runs roughest.
When driving, it runs smoothly if your foot is steady on the pedal.
If you accelerate, it surges and seems to have a light intermittent miss.
If you decellerate, it runs roughly for a time until it you steady the pedal again.

None of the tune up stuff worked, and it continued to decline.
The fact that it runs worse when moving the pedal, we checked the TPS.
It was .7v closed and 3.4v WOT.
The steady wire was 4.6v.
I thought the numbers were wrong, so we replaced the TPS with new.
No change.

All grounds have been checked.
When it is missing at idle, pulling plug wires or injector wires doesn't seem to find anything. There is no one cylinder that seems to be a culprit.

Anyway, the engine has lost a great deal of power under load.
Surging acceleration.
It runs fine at high rpm, so long as you have a steady throttle, so we have shied away from the one last 'tune up' item we haven't done, which is fuel filter. It doesn't act like it is running out of fuel.

We checked for vac leaks, none are apparent.... I know they can be tricky though, and even the brake booster could leak, but we have no reason to believe this yet.

Ideas?

Oh, module and coil are only a few months old, and the fact that it runs better warm are contraindications for failure of these items. We do have known good spares though.

 

[Mustang5L5]

Run the check engine codes.

1988 Mustangs do not have a check engine light. The spot is there, but only the California cars had them functional. So you would never know if it's lit right now. There is a way to make it functional, but it's complex and i rarely see anyone do it

Plus, only 13 of the the 100 or so codes actually cause it to light. It's not like an OBD2 system

Pull the codes, and run a cylinder balance test and report back what you get. If you search for this info, you'll find a lot of post by jrichker explaining how to do both. It's pretty much a daily post of his

 

[jonbacon]

I'd check the PVC, I swore to these guys while checking the list and I had no leaks. it was Barely in and was causing the same issue you are having. I went through all the same parts and when I finally touched the metal part of it, I saw it wasnt seated all the wasy. So I would double check Vac leaks. I swore I didnt have one then had to eat my words..
depending on when the last fuel filter was chanegd, that probably cant hurt either..but From my 3 weeks of Hell...it was a vacuum leak.

 

[jrichker]

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
Or for a nicer scanner see http://www.midwayautosupply.com/p-7208-equus-digital-ford-code-reader-3145.aspx– It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

 

[Gunmetal5oh]

1. Change the fuel filter, 2. Check and make sure a wire did not come off an O2 sensor, and 3. Check the resistance of the plug wires.
All you do is connect your multimeter to the wire, one lead on each end of the wire with it set to read Ohms. Ω
General rule for a good wire is 500ohms PER FOOT. High dollar wires can be as low as 50ohm, but unless you spent big money on wires you won't see readings that low.
Example, if a plug wire is 1 foot long, it will read 500ohms. A wire 1.5 feet long would be 750ohms. If you go through your wires and calculate out what each one should be given their length and one is not consistent with the rest, then you know you have a bad wire.

AFTER verifying the wires are good, hook up an inline spark checker.
Increase RPM slowly from idle to about 3500-4000RPM and verify consistent spark. This should let you find it, it doesn't sound like it's only happening when under load.