Help! Tired of throwing money at problem.

[DRock9]

I have had this problem for a long time I will describe the situations where it happens.

I have replaced the fuel filter and put in a brand new BBK 255lph fuel pump which I thought were the culprits.

Sitting in driveway idling, if I give it throttle to redline it is fine but it will backfire when it isn't heated up.

When I get in my car in the mornings I gun it down the street and it runs good and power through the whole RPM range but when I let off the throttle it backfires badly.

Once it warms up and I go WOT it will start breaking up really badly at about 3,000RPM and start pretty much bucking and jerking until I let off the gas.

If I rev it slowly it does not do this, and if I sit in the driveway and rev it in neutral it does not do it either.

Just for the heck of it I put in 93 octane today when I got really close to E and it did nothing.

Could it be a timing problem? I thought it was a fuel because it only happened under WOT with heavy accelleration so I ruled out anything in the ignition.

Please someone help me! I am tired of throwing all my money at this problem in hopes something will fix it, I have even bought two brand new O2 sensors and they did nothing.

I pulled the codes a week ago and they were:

KOEO: 31
KOER: 12, 21, 41, 91

Thanks for any and all help! It is appreciated!

 

[2000xp8]

Sounds like timing to me.
What do you have it set at?

 

[DRock9]

I have no idea, how can I check it?

I bought the car completely stock from its only previous owner and I did not bother asking him if he changed it because I assumed he didn't.

Maybe the chain jumped a tooth?

 

[2000xp8]

No, i don't i've ever heard of a chain jumping a tooth on a mustang.
Get a timing light, and search out a write up on checking the timing, one of those things that seems intimidating, but is pretty easy.

 

[88mouse]

mine is doing the same thing. I cut if off today to work on my coupe and it won't start back. But yesterday i pulled the cap off and there was oil inside my 8 month old dizzy. so i pulled the dizzy out and pulled the module off and there was oil all over the back of the module. So im guessing that the oil ****ed up the PIP in the dizzy. Because i have no spark now at all.

 

[DRock9]

Update: Putting in 93 octane DID NOT fix it!

I was just going through the center of town and go to cross 2 lanes of traffic and my car just falls FLAT ON ITS FACE! I almost died, it would not go anywhere it was just knocking/pinging so I got off the gas revvd it and dropped the clutch and went.

On my way home from picking up the pizza I floored it to see if all was well and it is still breaking up horribly after 3,000RPM.

So I guess it's not the timing? Clogged injector? I don't know.

 

[89roadster]

If you have not already, replace the cap and rotor, wires, and plugs, then set the timing. Clean your MAF, TB, IAC, and throw a can of fuel injector cleaner in. This is all just regular maintenance and then see if you still have the problem - it would probably be worth wiping the computer memory out after doing this.

 

[DRock9]

I just had a tuneup about three months ago after I again tried to go through the center of town and had the car fall on its face and would not want to go anywhere for about 5 minutes.

I have cleaned my MAF, TB, and IAC and put injector cleaner in a couple months ago but I will try the cleaner again.

Thanks!

 

[cjones]

31 EVP circuit below min voltage. do you have the vapor canister hooked up?? the EVP is a solenoid between it and the intake.

codes 41, 91 - O2 sensors show lean

21 - ECT -Engine coolant temp sensor out of range. was the engine warmed up before you ran the codes??

12 - unable to control RPMs selftest upper limit. if you disconnect the IAC while the engine is running does the idle drop??

 

[DRock9]

If I disconnect the IAC the car dies...

The engine may have been warmed up, I think it was but I will pull them again tomorrow to see.

I am not sure what the vapor canister is, is that the charcoal canister?

But you're telling me the car should still idle when you disconnect the IAC?

 

[cjones]

the flow chart for the 12 code asked(about the IAC)...the next step is to verify the 31 code is present so let me know the codes tomorrow.

yes, the vapor canister is the charcoal canister.

 

[joel5.0]

cjones....a little clarification if I may......31 has to do with the EGR Valve Position (EVP) sensor....not the CANister Purge (CANP) solenoid.

 

[cjones]

cjones....a little clarification if I may......31 has to do with the EGR Valve Position (EVP) sensor....not the CANister Purge (CANP) solenoid.

just shoot me now...i guess i need to get more than an hour or two of sleep a night. i should know better. thanks


if i keep makin stupid mistakes like that...no one will listen to me

 

[DRock9]

So the car IS supposed to idle when you disconnect the IAC?

Mine dies...so what does that mean.

 

[cjones]

So the car IS supposed to idle when you disconnect the IAC?

Mine dies...so what does that mean.

that is just for a specific test for the code 12 that we are diagnosing.

Start engine, disconnect IAC harness connector: 'does RPM drop or engine die'?
if yes, go to KE2. if no, go to KE3

since it died, we go to K2. Are codes 31, 32, 33, or 34 present?? if yes, go to QuickTest Step 7 for appropriate pinpoint test. if no, go to KE3

 

[89roadster]

Does it make a difference with what BRAND of gas you use? I used to have a stumbling problem because my fuel filter was clogged (with only 20k on the filter!) and certain brands seemed to flow better through the clogged filter than others. In the end I didn't figure it out until it had killed the fuel pump. This only happened after it warmed up the car and it would seem to stumble for a while then recover. At the very least try replacing the fuel filter if you haven't already.

 

[jrichker]

The key to your problem is the 41/91 codes. Since your O2 sensors are new, the odds are you have a lean condition.
The backfire tends to confirm that diagnosis.

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
Note that that if the outside air temp is below 50 degrees F that the test for the
ECT can be in error.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are
different animals. The ECT sensor is normally located it the RH front of the engine in
the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate
readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is
a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower
intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from
the rear. A pair of safety pins may be helpful in doing this. Use care in doing it
so that you don't damage the wiring or connector.

Here's the table :

50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

A faulty ECT sensor could cause the lean condition. I would check it out and then start looking for vacuum leaks.

 

[DRock9]

Thanks, that seems like it could be the problem.

My idle is good I start it up and there is no variation or surging, maybe every minute or so there would be a +/- 25rpm twitch but nothing consistant.

Quick question though, how do I know what temperature the ACT/ECT sensors are going to be so I can match it up to the table?

 

[DRock9]

I just pulled the codes again, after I reset them I took a 15 minunte drive with a few times at WOT and I got:

KOEO: 31, 67
KOER: 41,91

No 21 code this time...why is my car so inconsistant!

I have no idea what is going on.

 

[jrichker]

No matching of the ECT or ACT sensors is required. Ford specs the ECT/ACT sensors to have a +/- 15% tolerance,
so the table just gives you a midpoint value to compare your readings to. If it is way out of spec, more that +/- 15 %,
then replace the sensor.

If the readings are within the tolerance, then you need to start looking for vacuum leaks. This can be a trying and time
consuming process, since every joint and inch of the vacuum plumbing needs to be inspected.

Finding vacuum leaks:
I would avoid using anything that had a low flash point like carb cleaner or propane. Propane flashes very easily and a hot
engine compatment makes for a greater hazard. An old fashioned squirt oiler can with motor oil is a much safer and
easier method. The oil gets sucked into the leak and the engine changes speed. It is messy, but it is safe.

Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much
from engine to engine that it may be difficult to detect small leaks. My engine pulls about 16.5" of vacuum at 650-750
RPM, which I consider rather low. It is a mass market remanufactured rebuild, so no telling what kind of camshaft it has.
Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading
taken when your car was performing at its best through all the RPM ranges and what it is doing now.