Car falls on its face.

[bentley429]

For the past month or so my car has been hitting a brick wall at anything over 1500 rpm to around 4,000 rpm if I can mange to get it there the problem goes away. Basicly it sounds like it is backfiring through the turbo missing sounds like it almost shuts down then goes back up in the rpm's stumbling the whole time, yes this is while attempting to drive because of this I have prob driven the car 1 mile over the past month and it is really getting on my nerves. So far I started with:

New plugs
New wires
New cap and rotor
New TFI module
New distributor
New coil

Looked over everything 100 times. Pulled the codes several times and this is what I got:

Code 67(neutral switch, not a problem)
Code 85-canistor, dumped that so the plug is just hanging there
Code 22- Map sensor
Code 33- EGR(not hooked up)
Code 66- Mass air signal low

Car has edelbrock intake, world senior heads, f303, 72mm, 255 intank, 255 pusher, msd coil, 6al, msd cap and rotor, pmas pro tube for 42's, 42 lbs injectors, aeromotive stock line regulator. Timing is set at 10, FP is 40, has 10 inches of vacuum at idle( idle is set around 850) NO vacuum leaks anywhere.

I just pulled off the mass air and Iam going to the parts store to get some cleaner for it even though its brand new. This all started right after I let the dyno about 1/2 hour down the road it started stumbling and breaking up but not nearly as bad as it is now. The car is completely undrivable. Doesnt matter if the tune chip is in or out. Any help would be great thanks.

 

[jrichker]

Fix the MAP/Baro and the MAF codes and you will be good to go.

Code 22 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury - dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency meter to measure it. There is no way you can use a common cheap voltmeter or DVM to accurately measure the output signal.

The MAP/BARO sensor is mounted on the firewall behind the upper manifold.

Baro or MAP test using frequency meter - run the test key on engine off. The noise from the ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout.

If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

Some basic checks you can make to be sure that the sensor is getting power & ground:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.


Code 66 MAF below minimum test voltage.
Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

The MAF output varies with RPM which causes the airflow to increase or decease. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and ground. Make your measurement with the MAF disconnected from the wiring harness.


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

Computer,. actuator & sensor wiring
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Fuse panel layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Vacuum routing
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

 

[bentley429]

Ill pick up a Map sensor also then. Thanks

 

[GreatWhite]

I had the same problem awhile back... just clean out your MAF with a cotton swap and some rubbing alcohol. Dip the swap in the alcohol then gently brush the element inside the meter and let it dry. After you reinstall and hook everything up, you shouldn't feel that anymore. This is what I did after changing and checking numerous things, and this fixed the problem. Felt like a brand new car after I did it...

-- cj

 

[bentley429]

Cleaned the mass air which is brand new anyways with mass air cleaner and it didnt change a thing. Also swapped out the Map sensor even tried another computer. Nothing. Blew out a header gasket also so until I get that fixed I wont be solving the real problem. Have about 50 hours in this trying to figure out the problem and Ive had it for awhile. Planning on washing my truck and driving around in that, not that it matters but it will beat most close to stock foxs.

 

[GreatWhite]

Just junk it, man. Doesn't sound worth it anymore...

haha jk man

 

[bentley429]

Iam about to.

 

[a885.0]

Man these kind of problems suckkk, have you looked into the msd ign. box?? maybe look over all of the intercooler rubber couplers make sure there is no rips, or loose clamps.Iam sure its something stupid hang in there man..

 

[bentley429]

Yea I gotta disconnect the msd box thats basicly the only thing I havent tried yet but I blew a header gasket so Ive gotta fix that first before I can fixing out the stumbling deal. Turbo cars are a pain in the ass hopefully it will pay off.

 

[93 LX]

clogged exhaust system?

 

[riceslayer302]

keep trying josh you'll get it, you tried all that stuff i gave you and still nothing?

 

[bentley429]

clogged exhaust system?

Nope 3" DP into 2 bullets.

Yes tried everything, including the computer.