BIG_MODS

iTrader: (9)

7730 ECM
AutoProm
Accel Coil
Lots of clean-up in the harness (pics below)
Auto Meter Tach

I’m having a misfire (huff and puff stumble) at around 5k rpm, doesn’t matter if it is full throttle or part throttle. While this is happening the shift light is coming on, but in my chip I have 6k programed as the rev limiter.

I’ve also noticed while cruising down the highway that the engine will briefly miss and the shift light will start to flash precisely when going over a bump.

1 month ago while at the track the car ran fine right up to the 6k rev limit. Then it sat for a month and a half while I was getting the radiator repaired and now I have this problem.

I’ve checked while the car is stationary and not running:
Coil to ground- good
Coil is getting 12.33 volts with key on
Verified AutoProm zif is plugged in properly.

Lots of work (previously) has been put into my wiring harness to clean things up since the car is gutted and everything is visible. It is possible that I goofed something or a wire could be rubbing but I was careful to keep the wires from sharp edges.


I’m leaving for the Power Tour on Thursday and so I don’t have a lot of time to trouble shoot. I’m hoping my friends at TGO can point me in the right direction.


Some pics so you know what you’re working with here (not stock):
A pic of the interior and my IP:


This piece of aluminum holds the ECM, AutoProm, Fuse Panel, Relays, aux power, DRAC, and globs of wire:



Hinged at the bottom, remove a wing nut and it folds down.

So in other words, I could have goofed something here so don’t rule that out, but it ran fine a month ago.

RBob

iTrader: (1)

I recall this build now, the DRAC was the give-way. You added a 40-tooth reluctor on the output shaft of the Jerico, cool set up.

Check the grounds between the frame/body, battery and engine block.

The ECM case should not be grounded to the body. It is grounded via the ECM ground wires to the engine block. By also grounding it to the body this allows the ECM ground wires to carry current for other then the ECM.

Can use some of the rubber isolated standoffs. This is even better as it will also impart some vibration resistance.

It looks like the AutoProm cable end is plugged into a ZIF. If so remove the ZIF, and use a good machine pin socket. Even better would be a PROM into a machine pin socket. Myself and others have had problems with ZIF sockets.

The ECM may be going bad, looks like an AC Delco reman? I have a pile of them that are intermittent. The PCB traces/vias start to go open. Pull the cover off the ECM and with the engine running depress on the PCB at various locations.

Not a lot, just moderate pressure. If the engine stumbles or does funny things, it's bad.

RBob.

BIG_MODS

iTrader: (9)

RBob, Thanks for the lightning fast reply!

The car died on me at idle in the 95 deg heat yesterday and I had to trailer it home. It would start and run for short periods of time but die again. So I spent all evening getting the car home and had no time to trouble shoot.

Looks like you are spot on here. I did this test and it if I press in a certain spot it stumbles, repeatably. Going to get a new ECM now And I will be mounting the ECM using rubber isolators (this car is a tin can rattle trap no suprise that I killed the ECM).

RBob

iTrader: (1)

That will do it. With the number of '7730s I've tested I was surprised at how many failed this test. GM had to have received a huge batch of bad PCBs.

RBob.

BIG_MODS

iTrader: (9)

It hasn't died on me yet, but it is still having the high rpm problems

I'm going to try un hooking the tach and shift light. Also going to plug in the PC.

BIG_MODS

iTrader: (9)

New(junkyard) ecm mounted insulated and isolated to chassis
Tested with the shift light unhooked
Tested with the tach unhooked
removed the Autoprom and installed burnt chip in G1
removed ZIF from G1 and using pins

It still consistently coughs at 4600 rpm. If I roll slowly into the throttle it first coughs at 4600 and the shift light comes on. What could cause this? There isn't much to the ignition circuit. Am I correct in thinking this has to be in the ignition circuit since the shift light comes on whenever it coughs? If the tach wire was grounding out somewhere what would the shift light interpret that signal as?

The next thing I will do is check mechanicals – cap & rotor, ignition module (which is less than year old), ohm out the wires to distributor.

BIG_MODS

iTrader: (9)

Also, it has a VSS code, which it has had for the past year. Dunno why this isn't working anymore.

Also has solid engine mounts. Could have I killed a sensor from the vibration? If it reaches a resonance high speeds and blakes out?

BIG_MODS

iTrader: (9)

Just replaced distributor, cap and rotor.

When doing a 'slow roll' in 2nd gear (for example) it coughs at around 4600 and the shift light still comes one while doing that.

During WOT it coughs through that point but the shift light must not have time to light and it pushes through.


Besides checking to make sure they're not loose and ohm'ing them out, how do you check grounds?



So I'm hoping that this 4600 rpm problem and the stalling problem (with the ECM) are unreleated and I'm going to take off 3 hrs to Muskegon for the HR Power Tour. But I have the trailer loaded to the truck sitting at home with the father inlaw on call

RBob

iTrader: (1)

Sounds like something in the distributor isn't right. And the ECM is getting multiple distributor reference pulses (DRPs). This would have the ECM seeing a higher then real RPM, turning on the shift light and hitting the rev-limiter (cough).

I'm not a fan of aftermarket ignition parts. For coils, distributors, and modules, GM only. I will use a good parts house pickup coil though.


To check grounds measure the voltage drop. Say from the battery to the block while cranking the engine over. Can also do things like turn on the headlights for block to frame grounds testing.

RBob.

BIG_MODS

iTrader: (9)

I had a friend in the car data logging on Thursday night in Muskegon and we did about 50 4-6k pulls at various TPS. He was looking at all sensors for anomalies and found none. This issue seems to be temperature related as it was a cooler night and we couldn't get it to reproduce until the car had time to get warm and soak. This explains why I didn't have the issue in April at Waterford as it was snowing that day.

Good news is I made it to 3hrs to Muskegon and back and this issue did not cripple me though I have other mechanical issues that I need to fix.

Next steps are to replace the Accel coil with a stocker and do the ground check like you describe.

RBob

iTrader: (1)

If changing the coil doesn't do it I'd get a GM ignition control module in there. The one that ends with a part number of 369 is the one to get. I usually get them from a truck u-pull-it yard.

Note that the pickup coil may also be getting intermittent. Can't hurt to do both at the same time. And check the star wheel on the shaft. Make sure that it is tight to the shaft and that the magnets are in good shape. Can still buy the shaft/wheel assembly.

I know it sounds like 'replace everything in the distributor', 'maybe better to buy a new one'. But, unless it is a new GM distributor, don't do it. I've done what I've stated above by doing a complete rebuild with GM parts.

Although, the pickup coil, cap, and rotor, I'll use a good brand from a parts store.

RBob.

TTOP350

iTrader: (8)

Whats your plug brand and gap at? are they tight?

DAVECS1

iTrader: (2)

Man Big Mods, I wish I would of read this post before PT. I was in Muskegon and I would of loved to see your car. Funny thing is while traveling through that area I was having the same problems you were describing. I spent the night at a resort by lake michigan messing with all my ignition stuff. I think my problem was plug wires. I notice wire 8 was fouling the coil mount pretty hard. It seemd to be ok on the way home but I never ran it over 6K again just incae. Pops at that RPM really seems to stress things out.

I am thinking if I still have a problem the pick up coil is my next place to investigate. I have had this issue quite a few time on different cars. THe car runs well enough to get around but breaks up under stress. Change the pick up coil and all problems solved. Never really found a good way to trouble shoot it either. The range in the GM service manual is so large, the only thing you will find is a straight dead short, or open. For under 10 bucks it is a easy part to replace.

I use an MSD distributor, now. I am not sure if it is an improvement or not, but I was routinely going through my GM distributor to sort out issues above 5500 RPM. It is hard to find ignition modules that are reliable in that realm. I have been using a second strike box that seems to help the situation, but it does not replace the ignition module. I have thought about stepping up to a MSD box, but I have scene so many fail at the worst times.

Good luck on finding your problem.

joey 350 LT4

damn some one with the same problem as mmmeeee!!! my car when cold runs like a champ and when its at about 175 according to stock gauge if its moderately cold out. but past that whence heat soake sets in and temps go above 180 ish and if its like 80-90 degrees out side under WOT its stumbles at 3000 then again at like 4500 and symptoms increase as everything gets hotter. ill be checking mine out tonight. also i have all msd with taylor wires accel cap and rotor and parts store ignition module. ill be ohm testing the wires an im going to check the injectors in case i have a dead one. also all parts are at about 1 year old. if i find anything that will help ill let you know.

88305tpiT/A

iTrader: (2)

This sounds like issues I used to have. Turned out to be combination of many things but start with the wiring first.

Check the EST wire connection. Ive also had ignition modules in the distributor go bad in ways just like you are describing. They work fine cold then as the distributor housing heats up they start malfunctioning. Factory connections to the module and coil are also great culprits here. Most will present as intermittent if you still have the factory harness after all these years rotting away...

BIG_MODS

iTrader: (9)

I've been busy fixing other problems (hydraulic throw out bearing again, exhaust, radiator again) and got around to changing the coil. Coil is not the problem. I also moved the 1 ga engine ground and that didn't fix it. Going to check more grounds now.

BIG_MODS

iTrader: (9)

yeah, Dave, we were supposed to get in touch before the HRPT. Sorry, it was a stressful couple weeks prior for me and I didn't even think about. Hopefully you fixed your problem.

DAVECS1

iTrader: (2)

As far as I can tell I had a wire arcing to the plate I made to mount the ignition coil. Once I rerouted the plug wire the IAC started working correctly and the mis went away. I am hoping that was it.

Did you replace the pickup coil in the dizzy?

BIG_MODS

iTrader: (9)

I replaced the whole distributor (Advance Auto piece).

The plugs are Champions as recomended by Trick flow, gapped to .035. I went through and tightened them.

I also made sure the coil was grounded well and replaced the coil wire.

no dice

Going to try and find GM ignition module as recomended by Rbob. If that does work I can always do an LSX swap

BIG_MODS

iTrader: (9)

Could solid engine mounts be causing this?

DAVECS1

iTrader: (2)

Did you try pluggin the prom directly into the ECM? Try isolating the coil trigger wire also. Wrapping it in aluminum foil is a good test. If that works it needs moved or shielded as it is picking up interference.

Try grounding that electronics plate really well.

Plug wires suck, but can often have strang failure modes. Trust me I know the feeling. These gremlins seem hopeless and everyone's suggestions U have already tried or ruled out. It will come though, it just takes time and dumb luck, sometimes. Do not give into the LSx man:-) I need some hi-po SBC gen I friends!

THe other day we replaced everything on my friend's 455 GS and it would still misfire at 4500. everthing was different including the motor. We fixed the initial problem at some point, but figured out after three days and some money that the dial back timing light we were using was broke and causing our issue. MAn we drank after that one!

BIG_MODS

iTrader: (9)

Yes, the Autoprom and ziff socket have been removed

LMAO!

Yeah, I’m breaking some rules that I was taught by the mechanics I used to work with. They’d do all the tune up type stuff first no matter what just to make sure they are working with a clean slate. Might be worth my time and $ to through new plugs and wires at it even though it doesn’t seem logical.

I’ll try your other suggestions, and thanks for the encouragement!

Currently I have the valve covers off the car. Some people on the FRRAX forum are telling me that mechanical issues have caused misfires, so I am currently checking my valve springs.

RBob

iTrader: (1)

Make sure that all engine grounds are on iron, not aluminum. This is battery minus cable to the block, the EFI harness grounds, and any engine to body grounds.

Grounding to aluminum is dicey as it skins over over time and creates a higher resistance.

RBob.

92blazenchicken

i had the same problem on a old 5.0 mustang i had lol it could be a couple of things o2 sensor could be bad and causing car to be running lean at high rpms could have a bad injector or even a slightly burned plug wire thats arcing could cause it

BIG_MODS

iTrader: (9)

While running it is almost nothing ~0.001 V from head to chassis
While cranking it is 0.03V from head to chassis

I don’t assume that I have a problem here? I have not checked from battery (-) to block yet, that will be slightly more difficult.

DAVECS1

iTrader: (2)

What did you find out on the valve springs? Is the miss in the same spot everytime? Did you make a tunning change when this started happening. Maybe you have a bad cell in your tune. I had one cell once give me all kinds of fits, did no see it untill I opened the timing graph and noticed for some reason one of the cells was at -9 degrees.

BIG_MODS

iTrader: (9)

All valve springs appeared to be ok, both inner and outer. I pushed up and down on each one and looked at each with a flash light.

The miss is in the same spot every time, repeatedly when warm. The shift light coming on at this spot is inconsistent. I have opened the .bin file and looked for anything weird in the fuel and timing maps. I’m considering going back to an older file or even the SAUJP2 baseline. I did not make a tuning change when this started.

DAVECS1

iTrader: (2)

I had a motor do this once and the valv springs looked fine until i took them all out and lined them up next to each other and they were all diferent hights.

BIG_MODS

iTrader: (9)

The condition exists with 3 different dizzys, 3 different cap and rotors, 3 different coils, 2 different ECM's. I put in new plugs and wires this weekend and it seemed better but still there.

DAVECS1

iTrader: (2)

Do you have a data log??

Also you my want to take a dial indicator to each of the valves and confirm the health of your cam.

My be necessary to take the springs out and have them check also.

Another helpful bit of info before disassembling the whole thing is to go out and see if the problem shows up on a WBO2

Guest

Is that res bottle your blinker fluid?

BIG_MODS

iTrader: (9)

Good call Dave on the WBO2, its foolish not to try something simple like that. The thought has gone through my mind about the cam being toast as it is a flat tappet with over 0.5" lift with 1.6 rockers. Might try that also, but I'd think i'd be getting way more debris on my drain plug if the cam was shot. But there was a dirty oil change early in the life of this rebuild, so maybe that was it.

BIG_MODS

iTrader: (9)

yes

DAVECS1

iTrader: (2)

Well I found my misfire tonite! Working on my air conditioning of all things! I was getting the vlave cover out of the way when I noticed one of the screw terminal leads to the coil was about to fall out. I tightened it up and all is right with the world. It is the simple things usually. Just have to do the really complicated one to find it.:-)

BIG_MODS

iTrader: (9)

Dave, glad you found your miss fire. I'm sure mine is equally as simple and I will hate myself after I find it.

BIG_MODS

iTrader: (9)

I raised the rev limit to 10,000 rpm and the WBO2 shows super lean only during the misfire. Could a bad CTS or MAT cause a reaction this quick or does this only confirm there is a problem with the engine speed signal?

I'm going to try and data log, but I've have problems with my PC freezing up.

DAVECS1

iTrader: (2)

Unburnt fuel registers as super lean on a WB. That is probably not the issue. I would start checking the wiring. Check you voltage supply to the distributor and the coil.

BIG_MODS

iTrader: (9)

So on Saturday I said F-it… I’m going to the track tomorrow. Went to Grattan yesterday with the Michigan VW Club, ran the **** out of the car , had a great time, misfire and all.

Towards the end of the sessions the misfire would get worse, I’m guessing because of heat soak. Coolant temps stayed under control with the OE rad and oil would get up to 280. A couple times the misfire was so bad I thought the engine might have let go, but it didn’t. I found that how I harshly I shifted effected the misfire. With a fast, almost no-lift shift, it would stumble badly in the next gear and at times wouldn’t recover until I left off the gas for a second or 2. If I did a slower shift it didn’t have this severe problem.

Saturday (before the event) I pulled the valve covers again and re-set all the valves hoping I’d find one that was half a turn off or something. I didn’t notice such a thing and the test proved no change. The only thing that I found a little odd was it was hard to find zero lash on both of the #1 valves and I’m wondering if that is a sign of funkyness with the lifters. So I think I’ll pull the intake next and remove the lifters and see if I can see anything going on. I’ve also heard of a tool for checking valve spring pressures while they are still on the head? I have a car show / cruise event that my uncle puts on every year that I have to go to on 9/24. But before that I have some maintenance to do on DD’s so I’m not sure how soon I can get to this.

1MeanZ

iTrader: (9)

I did not know this. I'm not a wideband expert but I've never heard this. What is the difference between a rich mixture and unburnt fuel in the exhaust stream? I guess if the wideband is only measuring oxygen content in the exhaust stream then a completely unburnt charge could be expelled that would still have lots of oxygen content....

BIG_MODS

iTrader: (9)

I've never been so happy to find something broken:

DAVECS1

iTrader: (2)

So you just explained it to yourself. Temperature also plays a factor. A partially burnt mixture has distribution which brings it in to reading rich on the WB. A complete misfire will be cold and measured as air, and the liquid will not register.

Wow never sceen a pushrod fail quite like that. Congrats on finding the issue. I would check pushrod geometry. That looks like some nasty loading.

InfernalVortex

iTrader: (4)

A broken pushrod? Im guessing itw as broken at the lifter and not the rocker?

BIG_MODS

iTrader: (9)

Correct. The broken tip actually stayed captured in the lifter and the rest of the push rod was pushing on it so it functioned like normal most of the time. Hopefully this is indeed the source of my problem.

BIG_MODS

iTrader: (9)

Replaced all 16 pushrods with new set of Comps. Went 0.050" shorter than stock because that centered the roller on the valve better.

STILL HAS THE SAME FREAKING PROBLEM!

One thing that I've noticed is that during normal cruising (not at higher rpms) the WBO2 will sporadically show supper lean, like 20.9-40:1 only for a flash then it is back to normal ~14:1. I don’t feel or hear this brief leanness, only see it on the WB02. I’d say that this happens every 5-10 seconds. The same thing happens at 4600 rpm, but it is very DRAMATIC then. I don’t know what this means, but it must be a clue.

ALSO, when replacing my push rods I noticed that in some cases there is only 0.010" clearance between my valve springs and stamped roller tip rockers. I was concerned because I've seen videos like this: http://www.youtube.com/watch?v=i_Npz...eature=related and know that springs and valvetrain move around alot at speed. So I called Comp and asked, and the guy there said "as long as they aren't touching it is ok". I wasn't completely satisfied with that answer but I put it back together anyways. Not sure if this is something to worry about or not. When looking at the rockers there might have been evidence of rubbing on one rocker, but I couldn't tell for sure.

DAVECS1

iTrader: (2)

lifters while the pushrods were out? Also the valid lean limit on a WB02 is about 18:1 after that the signal is noise. Are you seing thes blips under acceleration? Cause on cams with large overlap during decel and and the fuel cut, it is normal to see the AFR spike lean.

Another less attractive problem is you have a valve not functioning correctly and you are passing a cylinder full of unburnt fuel. THis would cause those readings.

BIG_MODS

iTrader: (9)

no

It usually seems to hit 20.9 it seams. Sometimes higher.

Steady cruise. Decel it goes full lean, and I know that is normal.

BIG_MODS

iTrader: (9)

Could a bad sensor (MAT, CTS, TPS etc) be faulting out intermittently and cause the ECM to react immediately? Or would the ECM never react that fast?

DAVECS1

iTrader: (2)

The only one that could react that fast to cause an issue would be TPS. The air temp and coolant temp would cause issues with fuel mixture but they would happen over a long duration such as minutes and the problem would be a global variable affecting the whole fuel curve.

1MeanZ

iTrader: (9)

I 100% agree that everything but the TPS and the MAP sensor will cause slower global shifts. That being said, CTS and MAT can also throw your timing all out of whack too. If the ECM thinks the engine temp is 300deg and its really only 180 your timing AND fuel would be all over the place. When we datalogged your CTS reads *C, and I can't convert that in my head so we never did a "reality check" of that sensor's value.

I'll bring all my tuning toys to the cruise on the 24th and maybe we'll take another crack at it.

86T/A_Ram_Air

http://lmgtfy.com/?q=celsius+to+fahrenheit+calculator