Engine Code 66/98 Erratic idle

red5.0fox · Jul 11, 2022

So I have done research on this prior to posting this thread, but I’m not a wiring genius in any way shape or form and have been a little confused on following jrichkers checklist. Here’s what I have done to the car. GT40 upper lower intake, GT40 heads, 24lb injectors/BBK 24lb MAF, 70MM TB and spaced, CAI. I got the code not to long after I did the intake and injector swap. Since then, I have swapped the 24lb maf with another one and the code went away for a short period of time before returning. After doing some research, I figured that it could be a computer issue, and since I have one lying around I figured there wouldn’t be any issue in swapping it. So I swapped it, and the car ran great. Drove it around the block with a couple small pulls, and it didn’t have any missing or anything. That is a problem the car currently has, if I go WOT it’ll buck and stumble, but when daily driving it doesn’t mess up too much. Just idling and WOT. Hopefully you guys might have some ideas.

General karthief · Jul 11, 2022

Fuel pressure?

red5.0fox · Jul 11, 2022

General karthief said:
Fuel pressure?

I suppose that could be an issue.. I haven’t upgraded the fuel pump yet. I know all of the injectors are firing for a fact, so it would have to be just not enough fuel, right?

General karthief · Jul 11, 2022

Depends on the fuel pressure .
Have you done the checklist in order or did you skip around?
What year?

red5.0fox · Jul 11, 2022

General karthief said:
Depends on the fuel pressure .
Have you done the checklist in order or did you skip around?
What year?

Are you referring to the surging idle checklist? And it’s a 92.

General karthief · Jul 11, 2022

red5.0fox said:
Are you referring to the surging idle checklist? And it’s a 92.

Yes

red5.0fox · Jul 11, 2022

General karthief said:
Yes

I have done the checklist but not as of recent, suppose it might be worth a relook.

Mustang5L5 · Jul 11, 2022

I would look at fuel in terms of having an issue with your current setup, vs fuel supply not being sufficient. Your gt40 combo is rather mild and and could easily run on 19# injectors and stock pump. With that said, I agree with running 24s in this case, but it should still run on 19s

With that said, you just need to get a guage on there and see what your pressure is at idle and at wot. Just need to cross it off the list.

This could also be ignition related woth the usual suspects of the TFI/PIP/Coil. In fact, with it generating a code pointing to erratic idle, I’d suspect ignition over fuel given the tach signal is directly tied to it.

Still…gotta go through the motions and test.

If you erase the codes, what do you get now?

Stolen from Jrichker

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.

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.

If you disconnect battery and hook back up and immediately dump codes, you get a code 98. Need a few engine cycles first.

red5.0fox · Jul 11, 2022

Mustang5L5 said:
I would look at fuel in terms of having an issue with your current setup, vs fuel supply not being sufficient. Your gt40 combo is rather mild and and could easily run on 19# injectors and stock pump. With that said, I agree with running 24s in this case, but it should still run on 19s

With that said, you just need to get a guage on there and see what your pressure is at idle and at wot. Just need to cross it off the list.

This could also be ignition related woth the usual suspects of the TFI/PIP/Coil. In fact, with it generating a code pointing to erratic idle, I’d suspect ignition over fuel given the tach signal is directly tied to it.

Still…gotta go through the motions and test.

If you erase the codes, what do you get now?

Stolen from Jrichker

If you disconnect battery and hook back up and immediately dump codes, you get a code 98. Need a few engine cycles first.

Ahh ya I didn’t know that about the code 98 part. Suppose that makes sense. So I could cross that off the list of importance? It SHOULDNT be TFI as that is brand new and replaced, but we all know brand new parts can fail lol. I can toss a gauge on and see what the pressure is. I’ve got it in the garage now, I’ve done a wire tuck on the passenger side so I’m gonna pull off the fender liner and trace the wires to ensure nothing is broken or messed up. Every time I do something that may be a possible fix I erase the codes and run through it again. But even then, every time I disconnect the battery after doing something the check engine light comes back anyway.

Mustang5L5 · Jul 11, 2022

Does the 66 come back immediately? I’d chase that one down first

red5.0fox · Jul 11, 2022

Mustang5L5 said:
Does the 66 come back immediately? I’d chase that one down first

Yup immediately. I’m gonna trace all the wiring and make sure nothing is pinched or grounding out.

Engine Code 66/98 Erratic idle

red5.0fox

Active Member

General karthief

wonder how much it would cost to ship you a pair

red5.0fox

Active Member

General karthief

wonder how much it would cost to ship you a pair

red5.0fox

Active Member

General karthief

wonder how much it would cost to ship you a pair

red5.0fox

Active Member

Mustang5L5

That is…until I whipped out my Bissell

red5.0fox

Active Member

Mustang5L5

That is…until I whipped out my Bissell

red5.0fox

Active Member

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Engine Code 66/98 Erratic idle

Active Member

wonder how much it would cost to ship you a pair

Active Member

wonder how much it would cost to ship you a pair

Active Member

wonder how much it would cost to ship you a pair

Active Member

That is…until I whipped out my Bissell

Active Member

That is…until I whipped out my Bissell

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