DIS Failure symptoms?

[scottfab]

Originally Posted by XfireZ51

....snip...
If it is O/L as you point to here, then the O2 has nothing to do with it.

I'd agree with that. But please note in my post. The Open Loop suggestion was about speculation of fuel and is a separate paragraph.
The second paragraph introduces a separate suggestion (topic) and does not imply fuel or Open Loop.

Originally Posted by XfireZ51

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.

See paragraph issue above.

Originally Posted by XfireZ51

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 didn't speak to him but the OP said

Originally Posted by LGAFF

Having an issue, when I first start driving my 90, the car will miss and sputter for a short time(10 seconds) then run fine, no related codes..... as the exhaust is poping its unlikely fuel.
....snip...

He also mentioned that the car stalled and died once. Does your cal get run only after the first 10 sec or so? Could the problem be something outside the cal table? Could the MAP vacuum line have oil in it? And gurgles free? (sucked out) Or could it be a massively leaking injector whereby the excess fuel causes popping in the first 10 sec while being burned off?

Originally Posted by XfireZ51

I know that since its my calibration he's using.

I see

Originally Posted by XfireZ51

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.

I see, so because he's using your cal and the car has not been tuned it runs rough for the first 10 sec or so?

Originally Posted by XfireZ51

.... snip... And I know Lee's car has not been tuned properly for driveability. Given the specific conditions of Lee's problem,

I agree driveability is important.

Originally Posted by XfireZ51

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.

Sure would be a shame to spend a lot of time tweaking the cal only to find a failure in vacuum or a sensor or injector. While it is doable to fix or hide a hardware issue in software you can end up chasing your tail.

I'd agree with your assessment of O2 sensor if it's Open Loop only. I wonder though if it really is open loop only? Still the the reported issue goes away in 10 sec. Sounds like he needs to try a different chip (of any kind) to see what happens in that first 10 sec. Grabbing and using the most obvious symptom like the 10sec one seems wise.

The goal is to help get the car fixed. A step by step "what to try next" is in order. I'd say the next step has to be gather more info/symptoms.
Possibly attach a data logger if possible.

[Tyler Townsley]

Having chased DIS problems/differences for 2 years in getting Queenie running I can try to add some notes that helped me. A DIS module has 2 modes, under 400 rpm and over 400 rpm. Under 400 it runs on an internal logic ckt then transitions to the ecm control ckt. If you use a dis checker you can see on a scope the breakdown of the DIS if that is the problem. The car does not run when using this tester. I like to put a plug in each wire and lay them on the plenum. This does 2 things, it allows you to see the rhythm or lack of it. It also allows you to see if a specific plug has a weak spark.

http://thepandatrap.com/tyler/prototype1/90_ign_mod.jpg
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Not sure you have the above for reference. I will be at Britts next week moving Queenie from Detroit to the NCM for display and will have the checker with me. The advantage of this is you can run the complete DIS ckts with the plenum off the car and watch the signals on a hand held scope.

I tend to think the problem is not with the dis rather a leaking injector. I would start the car for about 5 sec and turn it off and pull the plugs looking for 1 that is wet/damp. You can then chase the spark or fuel delivery of the actual offending cyl.

Tyler

[LGAFF]

I did check the injectors when I pulled the plenum to replace the starter; not leaking under pressure, will pull the plugs and check

[LGAFF]

We can rule out ECM, swapped the ECM from my 91....same symptoms, will run it with a different chip today. I did run it with a different chip for a 368 w/ intake cams. I did not take it on the road, just around the neighborhood. It did seem to struggle after a few minutes and die(same symptoms as before).....but I want to test it under the same conditions and make sure it is apples to apples. The sputter and stall happened as I was backing...so hard to rule out tune at this point

[GOLDCYLON]

Originally Posted by LGAFF

We can rule out ECM, swapped the ECM from my 91....same symptoms, will run it with a different chip today. I did run it with a different chip for a 368 w/ intake cams. I did not take it on the road, just around the neighborhood. It did seem to struggle after a few minutes and die(same symptoms as before).....but I want to test it under the same conditions and make sure it is apples to apples. The sputter and stall happened as I was backing...so hard to rule out tune at this point

Lee just a thought since you have so many cars swap out the quad drivers. Will rule those out as well. D

[LGAFF]

swapped the eprom, same result....althought keep in mind maybe this one could have the same issue?

91 Vette Drs 368 with large intake cam, stock exhasut

[ZZZZZR1]

Originally Posted by LGAFF

Tested the fuel pumps each put up 50psi and held pressure....given the consistency between the two I think they are fine.

Fixed an issue with a 1991 Z in Florida that had a broken clip on the fuel pumps and it was intermittent Car was parked for 5 months because 2 mechanics couldn't troubleshoot it

His car would drive for 10 minutes and cut out / die consistently

Replaced the pumps / clips and issue was fixed

Not sure if this is our issue but thought I would pass along what I saw



David

[XfireZ51]

Lee,

A 90 won't run very well w an EPROM using a 91 calibration. Must be same BCC for that year car. Now it will run in any year ECM however. One other issue w the 90 prom is the knock filter on board later year chips while 90 is external.

[LGAFF]

Surprising although the motor was less responsive....idle and driving were normal

[LGAFF]

Got a code 64 finally I think that confirms its the 02; lean right