Runs Perfect in Diag mode, but hardly runs otherwise? Help!

[DrCheeto]

Hey guys, Another n00b HEI question.

My 93 started intermittently cutting out and not starting, and then one day completely lost spark. I went ahead and did the HEI swap as listed.

The Car runs now . Kind of. It runs SUPER rich, the exhaust pops like firecrackers, it surges, and won't idle by itself. I've triple checked the wiring, everything is as shown in the diagram...

It was running perfectly (when it would start) before the swap, now it's totally undriveable.. Any suggestions?

[DrCheeto]

Ok, So I hooked the original igniter back up and the car runs exactly the same.

I put the car in diagnostic mode to see if any codes could lead me in the right direction, and All I got was a VAF code (my fault , i had it unplugged when I started it previously).

I forgot to take the car out of diagnostic mode , and started it, and it runs perfect. No Popping in the exhaust, no gas fumes, idles fine....

WTF? I hate to sound so dumb, but I'm totally clueless on this one.


Any Ideas?

[Mad Cow]

Did you try starting normally with the VAF unplugged? Mine doesn't even start without it.

[DrCheeto]

It will start with the VAF unplugged, but it will only idle, I cannot give it any throttle.

When it's in diagnostic mode, it runs fine, but with no timing advance. When i disconnect the jumper, the timing goes all over the place, and starts running super rich.

I'm stumped.

[Mad Cow]

Unplug the battery and hold the brake pedal down for a few seconds, you might hear a relay click. That resets the ECU, could be causing your problem. I reset mine after I change any sensors or do anything with the electronics really.

[DrCheeto]

Unplug the battery and hold the brake pedal down for a few seconds, you might hear a relay click. That resets the ECU, could be causing your problem. I reset mine after I change any sensors or do anything with the electronics really.

That didn't help...

[Nd4SpdSe]

In Diag Mode, the motor just runs the way everything is setup, in regular mode, the ECU adjust everything. Maybe something is off, like your timing (or the disty rotated a bit) and the ECU is trying to compensate in regular mode, but in diagnostic mode, it runs fine, and the ECU doesn't adjust.

[Daninski]

In Diag Mode, the motor just runs the way everything is setup, in regular mode, the ECU adjust everything. Maybe something is off, like your timing (or the disty rotated a bit) and the ECU is trying to compensate in regular mode, but in diagnostic mode, it runs fine, and the ECU doesn't adjust.

WTF I uasually agree with your postings but this time, why would the ECU improperly adjust the engine? If something is off it would be worse in Diag mode as the ECU isn't trying to fix it eg. timing. So if it runs fine in Diag mode then his timing must be good.
I agree clear your ECU memory and once you do let the car run for 15-20 minutes so the ECU can relearn.

[Nd4SpdSe]

In Diag Mode, the motor just runs the way everything is setup, in regular mode, the ECU adjust everything. Maybe something is off, like your timing (or the disty rotated a bit) and the ECU is trying to compensate in regular mode, but in diagnostic mode, it runs fine, and the ECU doesn't adjust.

WTF I uasually agree with your postings but this time, why would the ECU improperly adjust the engine? If something is off it would be worse in Diag mode as the ECU isn't trying to fix it eg. timing. So if it runs fine in Diag mode then his timing must be good.

It's something that was encountered on Kp2t's car, but his timing belt is physically off, but the disty manually set to compensate in diag mode, it ran run, but in normal mode, it didn't. His resolution was to disconnect the cam sensor plug on the disty.

Like I said, and you said, the car is running good in diag mode, so everything is OK there, but in normal mode, it isn't, and in normal mode, that's there the ECU starts controlling everything, tweaking and adjusting to get optimal efficiency and performance. Obviously something not right, and I would guess it's something that the ECU is adjusting to make it wrong.

An ECU reset isn't a bad idea, maybe it's confused, literally, lol.

[Daninski]

When I installed the KL02 VAF I ran the car and it was ok then I cleared the ECU and it ran much better.

[DrCheeto]

Ok, wait... I'm confused here.

Wouldn't the car run WORSE in diag mode if say, my timing was off? From what i've read the computer runs on set values in diag mode, while not relying on the crank/cam sensors as a reference.

If say, my timing belt had jumped a tooth, or my disty was way off, I'd think that it would run WORSE on factory values than with the ECU trying to control it...

I guess what I'm getting at is, I know there are 2 crank sensors, and I believe a cam sensor. Does anyone have any first hand experience with one of these failing , and the symptoms they cause?

[Daninski]

Yes it should run worse as the ECU will adjust things to be within parameters such as your timing. Move your disty around and you'll find the ECU keeps it at approx 10deg

[DrCheeto]

Yes it should run worse as the ECU will adjust things to be within parameters such as your timing. Move your disty around and you'll find the ECU keeps it at approx 10deg

Worse in Diag mode or worse when not in diag mode?

I'm just thinking i'm going to wind up needing a distributor. I can pull the timing cover and double check the marks, but I really don't think that it jumped time.

[DrCheeto]

I think I figured it out.

I disconnected the crank sensor (the one on the pulley side), and it runs fine out of diag mode... I can't find my multimeter to test it, but at least i can drive it for a couple of days like this.

[mazdamx3freak]

sorry i didnt read this eirlyer. Yes your crank sensor is bad or in some cases just dirty. The reason your car is running in diag. mode fine is due to there beening a second crank sensor located inside your dizzy. Just replace the one near the crank pulley and it will be all better