Electrical 1992 5.0 Running rich with surging idle (surge checklist has been done)

1fstpnycb

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Aug 10, 2011
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I have been at this problem for months now and I can't seem to find a resolution so I'm hoping the more skilled people here can help before i start spending of money on having someone diagnose so here goes. I have seen several forums on my issue but everything i have tried doesn't seem to fix my problem. I have a 92 5.0 hatchback with some motor work done. Heads, cam, intake, piston, etc and a local dyno shop tuned the car. About a year ago now, I was just letting my car idle in front of my house and turned it off to go inside. I come back outside to start up and leave and I don't hear the fuel pump kick on and the engine won't turn over. I jumped on stangnet and read some of jricher's testing scenarios. After testing several things along the way, the fuel pump ended up staying on and not shutting off so somehow the problem changed on me. After changing the distributor injector pulse sensor with no luck, it ultimately turned out that the computer was bad so i sent it off to get repaired and when it came back, it still didn't work so i bought a computer from fox mustang restoration online and traded my core. I get the computer and plug up my performance chip, start the car, and it is immediately running rich and idling poorly. I attempt to drive it with no luck. Since then, at cold start it runs very rich and idles poorly. I will shut off and restart the car several times with no change. I will then go unplug the MAF and plug it back in several times along with backprobbing to test voltage. After several times of playing with the MAF, the car will start and idle cleanly and not be rich. To note, at this point the engine is warmer so if any sensors related to engine temp are being impacted by this, there may be a trend there.

So, i come back here and check jricher's surging idle checklist and this is what i've done and found to date.

1. MAF sensor check - I have a SCT BA2400 MAF sensor on a 90mm tube. After some initial checks, i was getting bad/inaccurate readings so i bought another BA2400. So far, I have backprobed both MAF sensors across pins C and D at idle and KOER, i was getting unsteady voltage from 0.4 - 1.00 on the original MAF sensor (on the car prior to the computer crapping out) and 1.00 on the newly purchased MAF sensor. When i idle up, i do see the voltage raise as i would expect. The issue i'm having at this point is i don't see a steady 0.6 volts and I don't know if both MAF sensors are bad or the computer i bought it causing this issue. To note, the car will run rich with bad idle upon initial cold start and after i unplug and replug the MAF in (i.e. play with several times) the car will eventually start, idle fine, and lean out. For the record, i still think the MAF sensor in some way is my problem but i don't know what else to do other than keep buying MAF sensor until one works.

2. TPS - I had issues a few years back with high idle at start and changed the TPS which fixed my issue. The TPS is only about 2 years old

3. Dump codes - I dumped engine codes KOEO and KOER and go the follow: KOEO- Code 66. I was messing with the MAF and unplugging and replugging in which likely threw this code. KOER, i was getting codes 21, 42, 13. I knew the car was running rich and I knew the idle was all over the place when I was dumping codes. It was surge to between 600 and 1400 RPM

4. ECT - Since i was getting code 21, i backprobed the ECT and got about 2.8 volts at ambient temperature and then would run the car and watch it decrease as i would expect down to about .9 volts. There was an instance where when i started the car i was getting above 3 volts and it was about 70 degrees outside so I decided to change the ECT just to rule it out. I now have a new ECT installed. Ultimately, I was getting pretty accurate readings through most of my test.

5. O2 sensors - the o2 sensors aren't that old and i wasn't getting a code for them so i have not changed them out. If there is a recommendation to do so, i can.


Ultimately, I have tried everything I can think off based on information from the surging idle checklist and help from my father who's an engine builder and his friend who is a mechanic and we just can't seem to figure this issue out. The worst part is that its not a consistent issue. At cold start, its rich and surging and after it warms up a little and i play with the MAF sensor enough, it will lean out and idle correctly. At this point, i don't know if its still the MAF, the computer i just bought causing an issue, or something else i still haven't checked or know about. The only thing that has changed from the car running fine until the point where i currently am, was a new computer. After the new computer was installed is when the rich running and idle problems began but i don't know if there is any correlation here or if the computer chip tune is reacting differently to this computer vs the other one.

Can anyone help??
 
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1fstpnycb

New Member
Aug 10, 2011
9
0
1
I have been at this problem for months now and I can't seem to find a resolution so I'm hoping the more skilled people here can help before i start spending of money on having someone diagnose so here goes. I have seen several forums on my issue but everything i have tried doesn't seem to fix my problem. I have a 92 5.0 hatchback with some motor work done. Heads, cam, intake, piston, etc and a local dyno shop tuned the car. About a year ago now, I was just letting my car idle in front of my house and turned it off to go inside. I come back outside to start up and leave and I don't hear the fuel pump kick on and the engine won't turn over. I jumped on stangnet and read some of jricher's testing scenarios. After testing several things along the way, the fuel pump ended up staying on and not shutting off so somehow the problem changed on me. After changing the distributor injector pulse sensor with no luck, it ultimately turned out that the computer was bad so i sent it off to get repaired and when it came back, it still didn't work so i bought a computer from fox mustang restoration online and traded my core. I get the computer and plug up my performance chip, start the car, and it is immediately running rich and idling poorly. I attempt to drive it with no luck. Since then, at cold start it runs very rich and idles poorly. I will shut off and restart the car several times with no change. I will then go unplug the MAF and plug it back in several times along with backprobbing to test voltage. After several times of playing with the MAF, the car will start and idle cleanly and not be rich. To note, at this point the engine is warmer so if any sensors related to engine temp are being impacted by this, there may be a trend there.

So, i come back here and check jricher's surging idle checklist and this is what i've done and found to date.

1. MAF sensor check - I have a SCT BA2400 MAF sensor on a 90mm tube. After some initial checks, i was getting bad/inaccurate readings so i bought another BA2400. So far, I have backprobed both MAF sensors across pins C and D at idle and KOER, i was getting unsteady voltage from 0.4 - 1.00 on the original MAF sensor (on the car prior to the computer crapping out) and 1.00 on the newly purchased MAF sensor. When i idle up, i do see the voltage raise as i would expect. The issue i'm having at this point is i don't see a steady 0.6 volts and I don't know if both MAF sensors are bad or the computer i bought it causing this issue. To note, the car will run rich with bad idle upon initial cold start and after i unplug and replug the MAF in (i.e. play with several times) the car will eventually start, idle fine, and lean out. For the record, i still think the MAF sensor in some way is my problem but i don't know what else to do other than keep buying MAF sensor until one works.

2. TPS - I had issues a few years back with high idle at start and changed the TPS which fixed my issue. The TPS is only about 2 years old

3. Dump codes - I dumped engine codes KOEO and KOER and go the follow: KOEO- Code 66. I was messing with the MAF and unplugging and replugging in which likely threw this code. KOER, i was getting codes 21, 42, 13. I knew the car was running rich and I knew the idle was all over the place when I was dumping codes. It was surge to between 600 and 1400 RPM

4. ECT - Since i was getting code 21, i backprobed the ECT and got about 2.8 volts at ambient temperature and then would run the car and watch it decrease as i would expect down to about .9 volts. There was an instance where when i started the car i was getting above 3 volts and it was about 70 degrees outside so I decided to change the ECT just to rule it out. I now have a new ECT installed. Ultimately, I was getting pretty accurate readings through most of my test.

5. O2 sensors - the o2 sensors aren't that old and i wasn't getting a code for them so i have not changed them out. If there is a recommendation to do so, i can.


Ultimately, I have tried everything I can think off based on information from the surging idle checklist and help from my father who's an engine builder and his friend who is a mechanic and we just can't seem to figure this issue out. The worst part is that its not a consistent issue. At cold start, its rich and surging and after it warms up a little and i play with the MAF sensor enough, it will lean out and idle correctly. At this point, i don't know if its still the MAF, the computer i just bought causing an issue, or something else i still haven't checked or know about. The only thing that has changed from the car running fine until the point where i currently am, was a new computer. After the new computer was installed is when the rich running and idle problems began but i don't know if there is any correlation here or if the computer chip tune is reacting differently to this computer vs the other one.

Can anyone help??
@jrichker I suspect you may have the most insight here. Any ideas?
 

jrichker

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@jrichker I suspect you may have the most insight here. Any ideas?

You have 2 problems, fix the MAF problem first.

Do you have cone filter in the engine compartment or 90°bend in the ducting for the MAF ? It sounds like the airflow through the MAF isn't smooth like it should be. Clocking the MAF may help some.

The cone filter for the air intake is a big NO-NO. It sucks up hot turbulent air from the fan and from around the engine. This disturbs the airflow through the MAF and causes an uneven air/fuel ratio. This cause many hard to find air/fuel problems such as surging idle, backfiring through the intake, and erratic throttle response. The stock airbox and flat panel filter is one of the best cold air intakes made. All that is needed is to take the silencer horn off of it.

Don't do this: it is a big NO NO.

attachments\562733


Try cleaning the MAF element & then "clock" the MAF by rotating the entire MAF housing to see if changing its position helps.

Code 13 & 415 - Key on Engine off - ISC did not respond properly (extends to touch throttle then retracts for KOEO) – ISC

Key on Engine running - Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too high)

If your idle is above 725 RPM, the computer will set this code. Normal idle speed is 650-725 RPM. Higher than that means that someone has mechanically set the idle speed by use of the idle speed screw, and has effectively disabled to computer’s ability to control idle speed.
 
Last edited:

1fstpnycb

New Member
Aug 10, 2011
9
0
1
You have 2 problems, fix the MAF problem first.

Do you have cone filter in the engine compartment or 90°bend in the ducting for the MAF ? It sounds like the airflow through the MAF isn't smooth like it should be. Clocking the MAF may help some.

The cone filter for the air intake is a big NO-NO. It sucks up hot turbulent air from the fan and from around the engine. This disturbs the airflow through the MAF and causes an uneven air/fuel ratio. This cause many hard to find air/fuel problems such as surging idle, backfiring through the intake, and erratic throttle response. The stock airbox and flat panel filter is one of the best cold air intakes made. All that is needed is to take the silencer horn off of it.

Don't do this: it is a big NO NO.

attachments\562733


Try cleaning the MAF element & then "clock" the MAF by rotating the entire MAF housing to see if changing its position helps.

Code 13 & 415 - Key on Engine off - ISC did not respond properly (extends to touch throttle then retracts for KOEO) – ISC

Key on Engine running - Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too high)

If your idle is above 725 RPM, the computer will set this code. Normal idle speed is 650-725 RPM. Higher than that means that someone has mechanically set the idle speed by use of the idle speed screw, and has effectively disabled to computer’s ability to control idle speed.
I do have a cone air filter but it’s up in the fender well and not in the engine compartment so that shouldn’t be an issue. I also can’t clock the MAF that im aware of the because the tube is bolted on in one location as opposed to held on by a clamp. Any other ideas you could think of?
 

jrichker

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I do have a cone air filter but it’s up in the fender well and not in the engine compartment so that shouldn’t be an issue. I also can’t clock the MAF that im aware of the because the tube is bolted on in one location as opposed to held on by a clamp. Any other ideas you could think of?
A piece of screen wire in front of the MAF or the screen wire from a stock 55MM MAF might help. There is supposed to be at least 6" distance from a 90° bend and the MAF body.
 
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1fstpnycb

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Aug 10, 2011
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A piece of screen wire in front of the MAF or the screen wire from a stock 55MM MAF might help. There is supposed to be at least 6" distance from a 90° bend and the MAF body.
@General karthief I attached a picture in this thread so you could see what I’m running but I have enough distance between the MAF and a bend. I can search for a screen. Would it be worth it to change to MAF wiring as well from the EEC to the MAF and buy a new MAF connector? What voltage should i be getting across C and D when uplugged from the MAF sensor? I was getting roughly 4.5 volts so I assume that is reference voltage?

@General karthief @jrichker Is there any chance that the EEC could be bad? The car was running fine prior to the EEC going bad and the only change was a new EEC.
 
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General karthief

wonder how much it would cost to ship you a pair
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Do you have the original maf and sensor?
you can clock the maf by unbolting the tube and loosen the clamp, rotate it to the next bolt hole, although I think this will do no good. I'm leaning to a vacuum leak. Also make sure the alternator is over 13 volts at idle.