Bad Hesitation

[Blurry Lines]

Hello everyone, I was wondering if you can help me please? I have a 93 GT AOD that I have had for 2 months and it ran great for that short time. Now the car is being a difficult.

Last Wednesday I was driving home and the car once warmed up to operating temp I went to pull out in traffic and the car acted like it ran out of gas. It will rev to 1500rpms before it will fall on its face like its out of gas. The car smells like its running rich also. This all happened and it was like a light switch was turned on.

The cars engine mods are Explore intake, 65mm TB, 75mm MAS, Shorties, Full Exhaust Shorties, no smog pump.

Since this all has started I have replaced some parts due to this issue and the prior owners
"repairs "

So far I have replaced the fuel pump and adjustable regulator and relay, set fuel pressure to 37-38 with vacuum on. I replaced the, IAC, TPS, Coil, TFI module, EGR sensor but not the diaphragm it held vacuum and prindle was clean, I also replaced the EGR vacuum controller. The EGR track in the intake and spacer are clean.

While the intake was off I replaced a lot of aging vacuum lines expecting that to be the possible culprit and that didn't work. I followed many threads on here and tested the power at the relay and the inertia switch that all had the correct voltages.

From what I have experienced so far the car rev's great when cold and will idle smooth but if any throttle is applied once at operating temp the car hesitates really bad or acts like there is no fuel or to much. This would be a closed loop issue correct??? The MAS is a 75mm Pro-M which looks to be modified due to the top looks glued on. I did clean it with approved cleaner and that didn't help.

The O2 sensors look newish, at this point I'm not sure were to look next???? I pulled codes but forgot them at the house this morning, I will post them tonight.

Any help will be great, Thank you

Richard

 

[jrichker]

You set the fuel pressure incorrectly.
Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line, cap the open end and stow it out of the way. Do not have vacuum applied to the fuel pressure regulator when adjusting the pressure. If you do, you will have it set way too high.
Connect fuel pressure test gauge to Schrader Connect fuel pressure test gauge to Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure : you should see 37-41 PSI at idle.
Turn the ignition off, reconnect the vacuum line and disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

 

[Blurry Lines]

Its a brand new adjustable regulator. What is the best procedure for setting the regulator and what PSI to see it to? It should be 39 to 42 with vacuum off?

I believe the cars problem is the MAS due to car will not rev past 1200-1500RPMS it just falls on its face and it will not clear up if pushed harder, although it idles perfect.

Please keep the advice coming

Thank you

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

 

[Blurry Lines]

I have pulled codes doing the KOEO test and all that I got was a 34 and a 11

 

[jrichker]

Its a brand new adjustable regulator. What is the best procedure for setting the regulator and what PSI to see it to? It should be 39 to 42 with vacuum off?

I believe the cars problem is the MAS due to car will not rev past 1200-1500RPMS it just falls on its face and it will not clear up if pushed harder, although it idles perfect.

Please keep the advice coming

Thank you

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

My previous post told you exactly how to set the fuel pressure. Go back and re-read it.

The too rich smell is because you don't have working catalytic converters. If you do have cats, no smog pump will cause them to not work correctly. The cat converters on 86-95 Mustangs must have the extra air provided by the smog pump. Without a properly functioning smog pump, the cat conveters will fail and clog. The smog pump shuts off at wide open throttle (WOT), so it only consumes 2 HP at most at WOT.

Have you done a full tune up and replaced the spark plugs, distributor cap, rotor and spark plug wires? Check the cap and rotor for cracks, and carbon tracks which would cause a misfire.

Does the problem happen more on a warm engine than on a cold engine?

You didn't get a code 66 for MAF problems. Did you dump the engine running codes too?
Disconnecting the MAF will produce a code 66, but the engine will still run without major problems. Try disconnecting the MAF and see if the symptoms change.

 

[Blurry Lines]

Jrichker, thank you for your replies and your help. I must of just not read the fuel pressure setting properly in your post. The car has been down since last Wednesday and has been a PIA in regards to transportation.

I pulled codes on the car before the resetting the computer because I didn't want to have the prior codes from the prior owner possibly cloud any current problems that I was having, in hind site a bad idea, it sounded good at the time. I kept the paper that I wrote all the codes down on before I cleared the KAM and here they are 34,66,63,46,13 with KOEO. I have yet to do a KOER.

I believe TPS has been solved in regards to Code 63. The IAC code 13 was solved, I replaced it and did the idle reset. I think 46 is the air pump and that was removed by the prior owner. That just leaves 66 and 34.

I will clean the EGR tonight and the MAS has been cleaned numerous times with the correct cleaner. The PRO-M that is on there now is at least 8 years old from talking to people that are familiar with there meters. The MAS looks pretty abused.

The car only does this once its up to temp, it runs good before in open loop and once it enters closed loop I believe that the correct way it works its all down hill from there. Any slight load (1200-1500RPMS) it falls on its face like its out of gas. I have a ECT sensor that is new that came with the car, thinking that might be worth installing?

Thanks again

Richard

 

[jrichker]

Code 34 Or 334 - EGR voltage above closed limit –

Revised 26-Sep-2011 to add EGR cleaning and movement test for pintle when vacuum is applied to diaphragm

Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat clean or, replace the EGR valve ($85-$95).

Recommended procedure for cleaning the EGR:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. There is a basket to set the parts in while they are soaking. Soak the metal body in the carb cleaner overnight. Don’t immerse the diaphragm side, since the carb cleaner may damage the diaphragm. If you get any of the carb cleaner on the diaphragm, rinse it off with water immediately. Rinse the part off with water and blow it dry with compressed air. Once it has dried, try blowing through the either hole and it should block the air flow. Do not put parts with water on them or in them in the carb cleaner. If you do, it will weaken the carb cleaner and it won’t clean as effectively.

Gunk Dip type carb & parts soaker:

If you have a handy vacuum source, apply it to the diaphragm and watch to see if the pintle moves freely. Try blowing air through either side and make sure it flows when the pintle retracts and blocks when the pintle is seated. If it does not, replace the EGR.


If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. 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 1.5 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1.5 ohm.

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.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.

The following sensors are connected to the white 10 pin connector (salt & pepper engine harness connectors)

This will affect idle quality by diluting the intake air charge


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).

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 pins A or B. 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


Swap your MAF for one compatible with your computer & tune.:
The MAF body and sensor are designed to match each other. Therefore you can't swap sensors between different part number MAF bodies and maintain proper calibration. The assembly is designed to match the computer’s internal program, and swapping a different MAF can upset the computer's calibration. In other words, your monster MAF probably won't match the calibration of your 5.0 Mustang computer.

The OEM Ford MAFs are not calibrated to injector size. The injector sizing is done in the computer’s internal programming. Aftermarket MAF’s “lie” to the computer in an attempt to fool the computer into changing the injector pulse on timing to match the increased airflow.

The only other MAF that is a one for one swap for a 93 and earlier 5.0 Mustang is the 94-95 Mustang MAF.

94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

Once your replacement 70MM MAF is in place, disconnect the battery for about 10 minutes. When you reconnect the battery and start the engine, the computer will relearn the settings for the new MAF.

*1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

 

[Blurry Lines]

Thank you for that information, I cleaned the EGR very thoroughly tonight and the vacuum held via the diaphragm and I couldn't hear any leaks while blowing in the either of the holes in the EGR housing.

I have a new MASS coming Friday from C&L, I inspected my old MASS and the gel inside the sensor is burnt in one area, no black visible but the area looked was extremely hot at one time. I guess this could be the issue??

I replaced the ECT because I had a new one spare. After all the work the car hesitates cold or hot now Idles great!!! Thanks to your recommendations I set the fuel pump at 38-39psi with the vacuum off.

I hope this new meter fix's the problem! I am not the best at a multimeter but I might have to get good at it. I will keep the post's current on my findings and what questions and help I might need.

Thank you again,

Richard

 

[Blurry Lines]

Well this is still on going, ready to have a bonfire. I traced a bunch of wires and the end result is I found the green 8 pin connector by the computer has the pink and orange wire and the pink and green wire has been stripped of insulation about a 1/4 inch of bare wire which might of shorted when I went of the railroad tracks when this first noted this problem. The railroad track are pretty rough.

Those circuits from what I can tell are tied into the VSS which I got a code for and the ECT,ACT, EGR, TPS and I think another sensor which I can't remember at this time. I got codes for these and thinking the computer was doing its job I replaced them and still left with a busted car. I guess this is good lesson test things out first before replacing parts, good inspector I was LOL. Here is the down side the computer smells not burnt but not a real good smell either and finding a computer for these cars that is a good match is interesting for my car being a 93 and auto.

I have tried the major chains and they are obsolete they say. I found a company that rebuilds you existing on and sends it back for 173.00. My main problem is that all sensors are new except the bap sensor so if the computer doesn't fix it what then? Other than those wires possibly shorting the computer out I am at a complete loss on whats going on?? I have never had a car that I just couldn't figure out.

The fun of a old car that to many people have had their hands in I guess. I have named the car Christine... dam car is possessed or its like my ex-wife and is just interested in money!

Anyone have any thoughts on whats left that I have over looked?

I even bought another vehicle to drive due to the issues transportation to work. I'm almost at the point of selling it...convert it to carb and send it on its way.

 

[jrichker]

Here's some diagnostic work for you to do that can help determine if your computer has problems.

Computer will not go into diagnostic mode on 91-93 model 5.0 Mustangs

How it is supposed to work:
The grey/red wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1.5 ohms when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe.

What sometimes happens is that the test connector grey/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60. Only an experienced electronics technician can open the computer up & repair the trace if it burns up and creates an open circuit.

The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring :
With the power off, measure the resistance between the computer test ground (grey/red wire) on the self test connector and battery ground. You should see less than 1.5 ohms.

If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the grey/red wire and pin 46 on the computer wiring connector : it should be less than 1.5 ohms. More that 1.5 ohms is a wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1.5 ohms. More that that and the computer’s internal ground has failed, and the computer needs to be replaced.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix for the computer internal signal ground.

If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More that 1.5 ohms is a wiring problem

The following is a view from the computer side of the computer connector.

wire side view of the computer wiring connector:

Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the grey/red wire goes. Almost every
sensor on the engine except the MAF is connected to it.

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

See the graphic for the 10 pin connector circuit layout.