DIS Failure symptoms?
 

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.

Thinking a coil or DIS but odd that it improved once you drive the car

No codes, I do get a code 61 but that is related to the tune/chip

It also waits to present itself between a shift...1-2 etc

Re: DIS Failure symptoms?
 

I doubt it's ignition if it improves. Sounds like warm up issues. Have you made any further mods to the car? What happens when you get off the throttle?

Re: DIS Failure symptoms?
 

If you need a DIS to check the problem out PM me Lee.

Re: DIS Failure symptoms?
 

The car has only died once, you have to modulate the throttle to keep it going, off the symptoms stop obviously.....engine pops and bucks pretty violently until it levels out.

Re: DIS Failure symptoms?
 

Thanks for the offer Frank, I have a few spares; I thought maybe it might just be a loose connection somewhere also...I had to replace the starter last night so I checked everything and the issue still presents.

I just find it odd that it improves with use

Re: DIS Failure symptoms?
 

This is a cammed car by the way

Re: DIS Failure symptoms?
 

Modulating the throttle suggests fuel. R U saying this happened on,y after replacing starter? Small vacuum leak? In between shifts, throttle closing, high vacuum, motor going lean.

Re: DIS Failure symptoms?
 

The ones I have seen go bad are total failures and one that was good below 400 rpm and fell apart above that. I had to use a dis checker to find that one.

Geoff has my checker at the moment but when I get it back you are welcome to use it. I will be picking it up 6 May when i move Queenie from Detroit to the NCM.

Tyler

Re: DIS Failure symptoms?
 

No it was happening before I changed it...I did not swap DIS as I thought it might be a vac leak

Fuel pumps are running 13.4 volts...pressure is normal

Re: DIS Failure symptoms?
 

I would think if it were lean I would not hear such pronounced popping in the exhaust

Re: DIS Failure symptoms?
 

Lee:

This might be a long shot, but I had a similar heat related misfire. I discovered that the female pin sockets in the ECM plug for the fuel injectors had been stretched by my volt meter and the corresponding male pins on the ECM weren't making good contact. Temperature and vibrations would cause a misfire that would clear again with no obvious clues.
Took me a dog gone long time to figure it out.

Good luck.

'Crabs

Re: DIS Failure symptoms?
 

So it happens when the car is warmed up and turned off then restarted?
That is the issue presents again for the first 10sec?

Re: DIS Failure symptoms?
 

Usually its after the car has sat:

Start the car, drive it down the block turn on the main road....bad shuttering popping. Always shortly after a startup, have not had it occur when its warm or being driven.

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

I think its the calibration; its fairly generic and I did not run the car in cold weather, car seems better today but its warmer and sunny.

Re: DIS Failure symptoms?
 

Lee,

If the car is cold and your hitting the accelerator and it stumbles, then the likelihood is the AE is too lean. There's a table for AE Comp v CTS or possibly
MAT that may need tweaking. At operating temp sounds like its ok.
I keep saying you can't expect a modded motor to behave without doing some custom tuning for it. It's not a question of just sticking in a chip and go.

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

While I agree, this was not present last year with the same tune....trying to rule out mech issues....thought maybe weather, not sure thats it

Re: DIS Failure symptoms?
 

Did you check too see if you have fuel in the tank?:-D:-D

I had a problem with my 90.. in Open loop car ran like crap, once in Closed Loop it was fine, it did similar things your car is doing. I swapped the ECM and it fixed it.. since you have a few cars, swap the ECM into another car and see if the problem follows, you could do the same with the Ignition module, move the one you think has issues into a car that runs fine. That is one way to narrow it down for you

Re: DIS Failure symptoms?
 

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....

Re: DIS Failure symptoms?
 

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?

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

:happy1:

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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.

Re: DIS Failure symptoms?
 

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.

See paragraph issue above.

I didn't speak to him but the OP said
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?

I see

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?

I agree driveability is important.

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.

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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

:cheers:

David

Re: DIS Failure symptoms?
 

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.

Re: DIS Failure symptoms?
 

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

Re: DIS Failure symptoms?
 

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