Engine cutting out...im at the end of my rope!!

[FLG]

OK so heres the story...

Car was running fine, no issues for awhile. One day im driving and i noticed between shifts it would flash a CEL and than it would go away...this eventually progressed to the point where at around 2500-3000 rpm if i was cruising..CEL would come on for a split second, engine would die, and than catch itself. Sometimes it will happen at lower RPM while switching gears. Some days is better than others, might not happen at all...might happen a bunch of times.

So after some checking, i noticed my crank sensor (which was new) wasnt in spec in terms of Ohm reading..so i replaced it. Same problem.

So than i just went on a spree and replaced anything that might have been it, some things (relays) i feel i should have replaced anyways due to them being as old as the car.

So heres what was replaced

-Crank sensor (also is withing proper distance from teeth on harmonic)
-Main and fuel relays
-AFM (used but resistance track looks fine, hasnt worn through)
-DME
-TPS
-Cleaned all grounds
-Temp sensor checks out good

There are no vac leaks.

The ignition system is only a few months old, oxygen sensor is also new

Heres what i noticed when this happens, i can ususally get it to happen in any gear but its easier to get it to happen in 5th when just driving along, its not very fun when it happens in 1st and your head goes straight for the wheel! Generally between 2500-3000 rpm.

One thing i noticed, when this happens the CEL come on and the tach drops down to 0 rpm (never quite gets there as the car catches itself before than) so im fairly certain this is not a fuel related issue as the tach would just move down as if i let off the gas, not shoot down as if it was unplugged.

At first i thought AFM, but this happens with BOTH of the AFM's i have...its possible there both worn out, but in the exact same spot? Also if it was the AFM wouldnt the tach still be reading correctly? I will try bending the tabs in the new one to have it cross a few part of the resistance bar but im not so sure its the issue.

Also i can only get this to happen while moving, engine idles absolutely PERFECT and i can rev it all day long passing 2500-3k and it will be fine.

I was also thinking that the harmonic might be bad and slipping causing the CPS so get messed up readings...but i feel it wouldnt be so RPM specific.

So im back to square one...maybe a bad AFM, maybe not.

Could also be wiring, but again..RPM specific, and makes no difference weather i hit a bump or not car could be on a smooth as glass surface and still cut out.

Im going to bend the contacts on the AFM tomorrow so it passes over a new spot on the bar, if the problem still persists...im out of ideas

The fact is, because the tach drops down my thoughts are either

CPS
DME
Slipping harmonic
Main relay

But CPS is good, checked out within spec

DME has been replaced, same issue occours

Slipping harmonic i feel wouldnt be so RPM specific and would happen even if i was revving it in neutral

Main relay has been replaced

[jlevie]

The tach going to zero in an event says that the DME is shutting down or loosing timing data. The flash of the CEL says that there should be stored fault codes if the DME isn't loosing power. The first action should be to see if there are any stored fault codes. Any fault codes retrieved are probably going to be a side affect of a loss of timing data rather than the cause of the events. But if there are no fault codes the DME may be shutting down.

Possibilities for DME shutdown include a problem with the main relay, its socket, or wiring. A bad DME ground (on the right front shock tower), bad fusible link (in the small cable from the battery), loss of START signal.

Loss of timing data could be a bad CPS, incorrect air gap between the CPS and harmonic balancer (should be 1mm), a problem in the engine wiring harness, or a wobbling harmonic balancer. If the toothed wheel on the harmonic balancer slipped, the engine probably would not run as the timing would shift.

To see if the DME is loosing power or START signal, connect a test light to the DME power input and see if the light goes out during an event. An led is the best choice. If the light does go out, repeat the test using the START input. Make sure the DME ground is good and check the resistance of the fusible link.

Make sure the bolts on the harmonic balancer are tight and see if the balancer wobbles when reving the engine. The balancer can do funny things when the engine is loaded if the front main bearings have a lot of wear. On one occasion I strapped a web cam & light into the engine bay and had a passenger watch while the car was being driven to catch a problem that only showed up under load.

If a known good CPS and a known good DME doesn't eliminate loss of timing data the engine harness is suspect. Changing the harness is rather a pain and there is no guarantee that a used harness will be any better and a new harness is rather pricey. But when you have tried everything else a different harness is all that is left.

I've used a battery powered storage scope to capture the timing input data to the DME to see what the signal looks like. In that particular case I'd been chasing this sort of problem for a year and a half. During that time every part of the engine management system had been changed once or more, the engine changed, and when the car was wrecked at Road Atlanta, the car was changed. The car at that point was on its third engine harness. It turned out that all three harnesses were bad, as proved by scope data. The fourth used harness was the charm.

I hope that other than the DME & AFM the parts you changed were new, not used.

[FLG]

Thanks for the input!

I will do some more troubleshooting today.

All the parts that have been replaced were new (less the AFM and the DME) the crank sensor was used but made sure it tested good before hand (didnt want to invest 100+ in a new sensor only to find out problem remains)

[Cinnabar325is]

, incorrect air gap between the CPS and harmonic balancer (should be 1mm)

Not trying to sidetrack here, just a fast question. How can you adjust the airgap (I know mine is more than 1mm). But the CPS bolts straight to its bracket and the bracket bolts straight to the block and there doesn't seem to be any built in adjustability.

Unless I'm missing something obvious, it seems I'd have to shave the bracket thinner to get the CPS closer to the trigger wheel.

[Keith M]

Mine did the same thing and I tested/replaced everything. As a last resort, I replaced the harness and the problem went away. It may not be your problem, but it's something to consider if you can't track it down.

[jlevie]

Not trying to sidetrack here, just a fast question. How can you adjust the airgap (I know mine is more than 1mm). But the CPS bolts straight to its bracket and the bracket bolts straight to the block and there doesn't seem to be any built in adjustability.

Unless I'm missing something obvious, it seems I'd have to shave the bracket thinner to get the CPS closer to the trigger wheel.

There is clearance in the bolt holes that secure the bracket to the block to allow adjustment of the air gap.

[jlevie]

Thanks for the input!

I will do some more troubleshooting today.

All the parts that have been replaced were new (less the AFM and the DME) the crank sensor was used but made sure it tested good before hand (didnt want to invest 100+ in a new sensor only to find out problem remains)

I've seen sensors with the correct resistance cause this problem. The only things I trust are a new sensor or a used one that I have proved is good (by using it on another car).

[FLG]

I had a new sensor on the car (months old) and even with the sensor change it still had the same problem. So im guessing its not the CPS sensor.

Air gap is correct.

I REALLY hope this isnt a harness issue. Ive went around and poked and prodded and moved wiggled as many harnesses as i could...no issues.

On another note, i pulled my plugs to see how they were....seems im running a bit lean and noticed some missing throught the rev range...thinking injectors need a cleaning. But ill worry about that later.

Also i removed the ground on the fender and cleaned it off, cars not movable ATM as i noticed the breather hose was very brittle and when i removed it, it broke...so waiting on a new hose before i can do any futher testing,

[jrdeamicis]

Ill throw out a left fielder.

Code relay control? It can disable your car from starting but if its dying it can turn on and off, flashing the CEL and killing the car for a second.

[FLG]

Replaced injectors man they were dirty.

Since I've cleaned the ground on the inner fender drove all day and so far so good...well see!

Sent from my Galaxy Nexus using Tapatalk

[SpecM]

Code relay control? It can disable your car from starting but if its dying it can turn on and off, flashing the CEL and killing the car for a second.

never heard of this

where is it?

[Keith M]

never heard of this

where is it?

Me neither. Please elaborate.

[TurboJake]

He's referring to the OBC code disable.

[Killacortes]

Same thing has happened to me man. I suspected a fuel related issue but sounds like its not. On my car it would hesitate just like how you said. Cel blinks for a second and all. I started using shell gas only and it went away. Weird I know. But that's how mine went away

[cabriodster87]

My car has a similar problem, except i have to disconnect bat to turn off CEL . So mine will stay off as long as i don't go WOT, it dies for that split second too. I give up so i unplugged it.