Engine 90 LX hesitation under load

HarshFyasko66 said:

So I was in neutral coasting to a stop. Car started to surge from 600-1000 rpm then died. She started right back up with no issues. The surge doesn’t happen at idle.

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Check these:
VSS Sensor
24lb injectors instead of 19's
ECU part number

Newb here. My 90, 5.0 5 speed has developed an occasional "stuttering" type of engine miss at low RPM and lite throttle. Running it up through the gears at full throttle (thru 3rd anyway) it seems to run smooth and strong like it always has. I only seem to get that "stuttering" miss when like cruising on a city street and I shift up to 5th and the RPMs drop around 1300/1400 and lite throttle just to keep up with traffic. Its intermittent and I can't "make" it happen.
Supposedly (as told to me by the guy I bought it from) it has a 303 cam and Explorer upper/lower intake and this "Intense Tuning" module. (please see attached pic)
All my years of fooling with cars told me it was a plug wire going bad. So, I put new plugs, wires, distributor cap and rotor. The miss is still there!
Incidentally, when I changed the plugs, all were burning that nice light tan color except #4. It was definitely darker (almost black) like it was burning more rich than the other cylinders.
Ideas?
Thanks in advance.

KaptKane said:

Newb here. My 90, 5.0 5 speed has developed an occasional "stuttering" type of engine miss at low RPM and lite throttle. Running it up through the gears at full throttle (thru 3rd anyway) it seems to run smooth and strong like it always has. I only seem to get that "stuttering" miss when like cruising on a city street and I shift up to 5th and the RPMs drop around 1300/1400 and lite throttle just to keep up with traffic. Its intermittent and I can't "make" it happen.
Supposedly (as told to me by the guy I bought it from) it has a 303 cam and Explorer upper/lower intake and this "Intense Tuning" module. (please see attached pic)
All my years of fooling with cars told me it was a plug wire going bad. So, I put new plugs, wires, distributor cap and rotor. The miss is still there!
Incidentally, when I changed the plugs, all were burning that nice light tan color except #4. It was definitely darker (almost black) like it was burning more rich than the other cylinders.
Ideas?
Thanks in advance.

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Piggybacking on someone else's thread is a very poor way to start you association on Stangnet. People get confused as to who posted what for what problem and it becomes very messy.

Start your own thread and I will do my best to help you.

Sorry bout that. Like I said, Newb here.
I'll try and start a new thread.

KaptKane said:

Sorry bout that. Like I said, Newb here.
I'll try and start a new thread.

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HarshFyasko66 said:

My apologies for being gone for so long had some issues come up with family then had to head overseas. Finally back and with the free time COVID has given me has allowed some wrench time in.

since I was gone from the car so long I decided to start from fresh.

Ran my reader for a KOEO test and pulled a code 11. Then performed a KOER test and got Codes for the O2 sensors showing lean. Along with MAF low voltage. These where the same codes as before so time definitely didn’t magically fix the car!

A friend of mine overseas mentioned the A9L computers sometimes having it’s capacitors corrode out can cause some issues. So I cracked the ECM open and instantly saw corrosion on said capacitors. I did some soldering work and noticed a few of the motherboard wiring routes looked damaged. I sent the ECM to a guy who repaired it and gave me a warranty.

I put the “new” ECM in and the car ranhorrible for about 10-15 mins then started to run fine.After a good 45 min drive it started to feel like it was missing and began to surge at idle and while under acceleration. Oh and the check engine light came on.

once I got home ran the KOEO test and pulled a code 11. Then performed a KOER test and got a code 98 and a code 66. Now the code 98 I’ve never seen before can anyone help with that? The manual for the reader says the ECM is in FMEM. I tried to erase the code by performing code clearing procedures of disconnecting the battery and turning headlights on but no success.

again sorry for the long post but I figured the more info the better. Thank you for any help and advice!!

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Code 66 or 157 MAF below minimum test voltage.

Revised 2 Nov 2019 to add details on MAF testing

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.

Computer wiring harness connector, wire side.


Computer wiring harness connector, computer side.


Diagrams courtesy of Tmoss and Stang&2Birds

ECC Diagram for 88-90 5.0 Mustangs


ECC Diagram for 91-93 5.0 Mustangs


94-95 Diagram for 94-95 5.0 Mustangs[/b]



How the MAF works

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. Changes in RPM causes the airflow to increase or decrease, 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.

Actually, MAF pins C & D float with reference to ground. The signal output of the MAF is a differential amplifier setup. Pins C & D both carry the output signal, but one pin's output is inverted from the other. The difference in signal between C & D is what the computer's input circuit is looking for. The difference in the two outputs helps cancel out electrical noise generated by the ignition system and other components. Since the noise will be of the same polarity, wave shape and magnitude, the differential input of the computer electronically subtracts it from the signal. Then it passes the signal on to an Analog to Digital converter section inside the computer's CPU chip.

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).
89-90 Model cars: 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.

91-95 Model cars: Measure the MAF output at pins C & D on the MAF connector light blue/red 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.

MAF output readings: Use the computer connector diagram to help choose the proper pin connection on the computer when measuring the MAF output voltage. The idling voltage check can the done with the voltmeter directly stuck in the backside of the MAF connector.

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

If the output of the C&D pins exceeds the specs above, there are two possible problems:

1.) The MAF sensor is defective and needs to be replaced.
2.) The MAF sensor is installed in a different housing than the one it was designed for. The sensor is designed to work with a specific MAF part number or model MAF housing.

Check the resistance of the MAF signal wiring
For the next 2 checks make your measurement with the MAF disconnected from the wiring harness.

Pin D on the MAF wiring harness and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF wiring harness 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.

Reconnect the MAF to the wiring harness and proceed to the next section.



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



Code 98 - basic computer internal tests not passed before it started processing the request to dump codes. Do a Key On Engine Off test before starting the engine. Wait until you see the 11 flash before pressing any buttons if you have a hand operated scanner. The computer is operating in Limp mode, so fix any codes it dumps prior to doing anything else.

These were codes i got:
Motor off 10 14 22 31 41 66 96
Motor on 6 21 41 31

my issue was totally different. Towards the end if i floored it, it would nearly die out completely till i let off throttle. Ie: no fuel (only knowing this in hindsight) it ended up being a fuel pump.... Not saying your is a fuel pump.

My point is: imo, i wouldnt worry about chasing most codes. From what i expierenced only though, so far, i didnt fix anything else and it still runs good with all those codes popping up. Idles good. Also it has loow compresiion on 1 cylinder if not 2. Burns oil like a syph (?) Has a stock MAF w/ 24lb inj. (Not my doing lol).

So my ultimate point is i bet its something simple/mechanical.

TFI, ignition coil, spark plugs.Something like that.

Thats how i roll. Im a guesser, but i try to use intuition and feel. Ive been lucky on a few problems i had. Though they did take some trial and error. Richker is an actual guru. So listen to him, not i. Lol. Just throwing my thoughts out there.

Now some codes may be more important, hold more weight for sure. Didnt read the end of his post before my post. Example: if code 98 throws it into limp mode, that's something i wouldnt ignore. Ok i would if it still ran strong. But. Lolol. Only if it ran strong.

I assume you'll clearly feel/know if ur in limp mode? (Thats what she said)