Runs like crap, hesitates, stutters, backfires

[s0lidllama]

Hey everyone having some problems with my stang hopefully someone has an answer. Dont flame either I've looked through every forum imaginable, I think i know the problem but right now I just want to verify what I think.

Ill include full detailed long story and the short story


Short Story:
Car stutters, hesitates, and backfires through intake. Sometimes while sitting on the driveway when I hit the throttle but most of the time when under load trying to drive down the street. Usually between 2500-3700 RPM. Once it gets past that its fine and has lots of power.

I think its the MAF it has a PMAS that is calibrated for my 24lb injectors. When I unplug the MAF it runs better (weird right?) and I have NO hesitation or stutter or backfire. So should I try replacing the MAF or what?

Long Story:
Got the car 8 months ago. It ran and seemed fine but upon closer inspection it turned out the timing was all jumbled up. Got the wires going in the right direction set the timing to 12* then the car started to have an idle surge.

Went through the whole checklist for surging idle. Checked the codes and came back with many. Notably code 66 and codes for lean condition on left and right side. Replaced fuel filter and finally installed a new idle air valve which had to be installed upside down for it to work correctly lol. The surging stopped but now I have a new problem:

First it started out with no power between 2500-3700 RPM's while in gear but would idle and rev fine. Every time I tried to drive from a stop as soon as it reached those RPMs it would stutter, hesitate, sometimes backfire through the intake. Replaced the o2 sensors thinking it was just a lean problem because the factory sensors were still in place and replaced the spark plugs. Ive cleaned the air filter and sprayed the MAF with MAF cleaner. Still the same problem but now its gotten worse. It will stutter, hesitate, and backfire even while idling when I hit the throttle on the driveway. Sometimes it will try to die out. Once it gets past 35-3700 its fine and has lots of power whether stopped or driving.

 

[jrichker]

The code 66 is a MAF failure. Fix the MAF problems before doing anything else.

Code 66 MAF below minimum test voltage.

Revised 12-Nov-2010 to add paragraph on clocking the MAF to check airflow through the MAF

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.

If you have a K&N flat panel filter or other filter that requires oiling, excess oil may coat the MAF sensor element and cause problems.

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).

Clocking the MAF is useful when you have a cold air kit or some other modification to the air box or air inlet before the MAF. Clocking is turning the MAF housing so that the sensor element is in a different position. It changes the airflow through the MAF to place the sensor pickup in the place where the airflow is the least disturbed.

Changes in RPM causes the airflow to increase or decease, changing the voltage output.. 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 Mustang FAQ - Wiring & Engine Info

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

 

[s0lidllama]

Thanks for your response first of all. Heres what I got.

MAF Voltage = 13-14V

Idle = .8V

MAF Signal Wire Resistance = wasnt sure how to do this. The only time i got a reading was only when i used one probe on the wire I did both:

C = 12-14M Pin 9 = O.L
D = 16-18M Pin 50 = O.L

Ohms with MAF unplugged:
C and ground = O.L
D and ground = O.L

So what does this mean?


I also tried clocking the MAF. Nothing changed

 

[s0lidllama]

bump...

 

[1990MustangLX50]

Did you unplug the MAF sensor and the ECU connector when you checked resistance from C and D at the MAF to the ECU. If you are getting OL then you have broken wires to your ECU. I doubt you have broken wires to your ECU from the sensor, your check engine light would of come on more than likely. I would try to find a known good MAF sensor to try and see if you get a change. A bad MAF would cause the issues you are describing.

 

[mob]

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.

This means that with your multimeter you need to put it on the ohms setting, and put one of the leads on the d pin, and the other lead on pin 50 on the computer. And read the number on the screen, it should read less than 2 ohms. This will indicate you have a solid connection between pin D and pin 50 on the computer and eliminate any connection problems in between. Same with Pin C on the MAF and pin 9 on the computer.

For the second one you need to connect one lead to the C or D pin and the other lead to ground and check resistance. I would go straight to the battery to eliminate using a bad ground. If you got O.L you may have used a bad ground. You can run small jumper wires to your multimeter if wire length is an issue.

The reason you are getting O.L is because you are not connecting the other lead to anything, so you have a O.L or Open Loop. If you get a 0.00 reading than you have no resistance between the two points and have a closed circuit.

Thanks for your response first of all. Heres what I got.

MAF Voltage = 13-14V

Idle = .8V

MAF Signal Wire Resistance = wasnt sure how to do this. The only time i got a reading was only when i used one probe on the wire I did both:

C = 12-14M Pin 9 = O.L
D = 16-18M Pin 50 = O.L

Ohms with MAF unplugged:
C and ground = O.L
D and ground = O.L

So what does this mean?


I also tried clocking the MAF. Nothing changed

 

[s0lidllama]

Thanks for the responses everyone

I was doing the Ohm readings wrong. Ill try again tomorrow.

On a side note:
If the MAF is indeed bad, if i were to replace the MAF with a stock unit would it still be able to read my 24lb injectors?

 

[Mustang5L5]

Do you have a chip or tune for the injectors? If not, you either need to tune for the larger injectors or get an aftermarket maf that is "calibrated" for the 24's

 

[nick6690]

I had the same exact problem. Turned out to be a spark plug wire that was laying on the headers and was burned up. Be sure to not look over the simple things like that.

 

[s0lidllama]

Do you have a chip or tune for the injectors? If not, you either need to tune for the larger injectors or get an aftermarket maf that is "calibrated" for the 24's

Supposedly my MAF is calibrated for my injectors. I have a PMAS but all the markings have rubbed off. It was on there already when i got the car

headers and was burned up. Be sure to not look over the simple things like that.

Ive looked at all the wires i have 7 ford motorsports and 1 yellow one thats probably accel. They look like theyre still functional maybe just old. That was another question i had though... Would bad wires cause this big of a problem? I have an MSD coil and the top that connects the coil wire to the distributor just kinda sits there because the clips have broken. would this cause a lean condition too?

Its been reading lean since before this hesitation problem started. Im about to check the resistance now.

 

[s0lidllama]

UPDATE:

Just finished checking the resistance. Everything seems to be good as far as the harness is concerned.
I was able to pick up a 24lb Granatelli MAF with 24lb injectors off ebay for 85 bucks. Im going to try that when it comes in. Is there anything else I should try in the mean time?

I also bought a new coil adaptor and plug thatll be in tomorrow. Should i go ahead and replace the plug wires too?

 

[nick6690]

UPDATE:

Just finished checking the resistance. Everything seems to be good as far as the harness is concerned.
I was able to pick up a 24lb Granatelli MAF with 24lb injectors off ebay for 85 bucks. Im going to try that when it comes in. Is there anything else I should try in the mean time?

I also bought a new coil adaptor and plug thatll be in tomorrow. Should i go ahead and replace the plug wires too?

Yea it definately wouldn't hurt. Plus they would all be matching

 

[s0lidllama]

Plus they would all be matching

Lol thats the real reason i wanted to get new ones

 

[mob]

Yea I would say something weird is going on if you have mix matched wires, mine as well change them. Good choice on getting the new MAF, thats a good deal if it comes with the injectors. Whether it was the wrong maf for your setup or it was just bad, this should fix your problem. Let us know. I would try and do some more research about the MAF you have, maybe you can resell it.

 

[s0lidllama]

Checked the plug wires tonight theyre definitely arcing. Gonna look at getting a new set tonight.

A friend of mine said that if my dizzy was wrong it might be upfiring like i mentioned. Any ideas on that?

 

[supr_sly]

did changing your wires fix all the problems? i having the same issue. i will be looking at my plug wires.

 

[s0lidllama]

just an update

did changing your wires fix all the problems? i having the same issue. i will be looking at my plug wires.

Sorry its been so long just thought Id update this incase anyone has the same issue.

I ended up playing with timing and adjusting the FPR till it finally just ran right. Fuel Pressure needed to be 50psi which seems really high to me and timing at 10* but it ran strong and hard

UNTIL

i changed the spark plug wires. As soon as i did that it went back to the same problem.

 

[s0lidllama]

Its like I go in circles with this car.

Anyways, car idles fine sounds like a kitten. My car sputters and RPMs wont climb past 2500(ish) RPM. Once it gets to that point it starts to die till i let go of the throttle. When the RPMs fall the car idles fine again

It seems like its not getting fuel but Fuel Pressure Gauge says its there.

I ended up playing with timing and adjusting the FPR till it finally just ran right. Fuel Pressure needed to be 50psi which seems really high to me and timing at 10* but it ran strong and hard

When I tried this again AFTER replacing the plug wires i couldnt get the same results as before

Could it be a timing issue, tune issue, or fuel delivery system?




No codes

Fuel filter is new

 

[stykthyn]

if you are not getting codes my hunch would be timing. Have you pulled the distributor and brought the engine to tdc?

 

[gt40_2003wes]

yea def find tdc and set you're timing and go from there