DIS Failure symptoms?

[XfireZ51]

Originally Posted by LGAFF

Well not too bad today, buts it warm...I had the tech 1 on and noticed the BLM Int went to 70 when it stumbled....

Right, its adding fuel and trying very hard to do that w an INT of 70. Its your pump shot and it needs to be adjusted for CTS.

VE table needs to also be tuned since the AE (Acceleration Enrichment) is a derivative. It ll starts at the VE table. What was the temp of the motor when it stumbled?

[rkreigh]

I had a DIS module get flakey on my 93. when the car would sit outside, and there was heavy moisture in the air the car would buck and spit and stumble until it ran enough to "dry it out"

thought it was just bad plug wires but it finally started to code (don't remember what it was, it was a long time ago)

as long as I drove the car often and it stayed inside snug, warm and dry, it never happened.

this was my LPE 475 car, ported, billet rods, forged pistons, stock cams

car only made 400 at the tire, which was really disappointing since I "thought" it was a 368 from the LPE dyno sheet (engine stand) that showed 563

seriously doubt that dyno sheet was from the car I bought

or it was the worse case of "happy dyno" I've ever seen

car was strong and ran great, but it wasn't anywhere 563 based on 400 at the wheels. and it needed a tune to get there. first few pulls were at 378. boy was I disappointed.

sorry for the ramble, good luck finding the problem

[scottfab]

Originally Posted by LGAFF

Well not too bad today, buts it warm...I had the tech 1 on and noticed the BLM Int went to 70 when it stumbled....

Sure feels familiar. What side went to 70? I mentioned this before, O2 sensor.

[XfireZ51]

Originally Posted by scottfab

Sure feels familiar. What side went to 70? I mentioned this before, O2 sensor.

Bad O2 would be consistently bad, not just when cold and at small AE increments.

[scottfab]

Originally Posted by XfireZ51

Bad O2 would be consistently bad, not just when cold and at small AE increments.

That would be incorrect. Sorry. You have to understand the different (many) failure modes of an O2 sensor.

[XfireZ51]

Ok. Please explain and then tell me how it explains the symptoms Lee is describing better than what I think the issue is.

[Funracer]

Originally Posted by XfireZ51

Ok. Please explain and then tell me how it explains the symptoms Lee is describing better than what I think the issue is.

[scottfab]

Originally Posted by XfireZ51

Ok. Please explain and then tell me how it explains the symptoms Lee is describing better than what I think the issue is.

I'm not going to go for "better". I'm going to caution about ruling out the simple things.

First read my previous post on one of the failure modes. (heater) then note the the O2 sensors can behave intermittence from a coating of contaminates on the zirconia element. I suspect the one I had that went bad of failing in this way since it worked fine sometimes then would go "lazy" sometimes. Once the system adjusts to they lazy O2 reporting (uses richer block/trim) then starts working well again the trim will go low) run lean until adjustments happen again.

Best isolation I did was to reset (battery disconnected) and collect data while running down the road. I could see the struggle.
I swapped the two O2 sensors and saw the switch side to side. I was fortunate to have the long leads on both.

We all know intermittent problems are the worst. I say rule out the simple possibilities before going to more elaborate ones. If this car had always had this issue it would be different. As it is I am left thinking it ran well at one time. (mods or no) So look for and proceed to isolate from easiest to hardest components.


1. consistent fuel pressure? (pump issues)
2. O2 sensors ? (intermittent)
3. injector ? (intermittent)
4. Redesign cals

[LGAFF]

Yes, ran fine last year....as noted...and maybe nor relevant, weather was much warmer(cal??)

I agree could be the 02, but it needs to be tuned also

[XfireZ51]

Originally Posted by scottfab

Sure sounds like it's OPEN LOOP related so yah I agree with others, fuel related. With the popping it sounds rich when in open loop. Maybe a nasty sticking open injector. Could be very time consuming to isolate. If you have a way to, find out what block/trim looks like on both sides.
Also comes to mind is the O2 sensor heater. It is suppose to bring the sensor up to temp fast. If the element is blown then it'll be slow to respond until the exhaust heats it up. Just some ideas, food for thought

Here's your post. And I am doing this not to be argumentative but rather instructive.
If it is O/L as you point to here, then the O2 has nothing to do with it. Whatever the fueling issue is dependent on the base VE table(s). In O/L, the O2 isn't causing the ECM to modify the fueling. Having spoken to Lee about it, it appears to happen in cooler weather and before the motor is up to temp. It doesn't go into C/L until about 75C CTS. I know that since its my calibration he's using. And because he's using a copy of my cal, I also know that it's likely a bit lean since his motor has both larger intake and exhaust cams while my cal is for a larger intake cam only. There are modifier tables for the AE pumpshot and one of them deals w CTS, another w MAT, and yet another on Delta TPS%. These modify the calc'd PW in the corresponding VE table cell his motor happens to be in. If the VE is lean, the AE shot will likely also unless adjusted. That's why it's so important to get the driveability right. It's the base of the tune. Everything else revolves around it. And I know Lee's car has not been tuned properly for driveability. Given the specific conditions of Lee's problem, I suspect the cal needs to be tweaked. To me this seems to explain what is being observed in a manner much simpler than a flaky O2 sensor. Especially if its happening in O/L.