Will Not Stay Running??

#1

My car will not stay running. Started doing this at Nationals after a qualifying race. Symptoms are that it will start, idle for a short time and then die. I can also start, idle, rev up and hold and it will still die. It is like it just shuts off. Battery is fairly new and I have replaced FPR, CPS, CTS, plugs, ECU, ICV, O2 sensor, and kill switch. Not all were changed for this issue but I listed them anyway. My AFM was purchased new a few years ago. I have confirmed I have adequate fuel pressure, The alternator is charging after being “excited”. It seemed that I could get through a race without issue but would die when getting to impund. Also, if driving it will cough and then catch again sometimes. I am thinking that with the car moving that whatever is being interrupted is back on line and with the engine rotating it just keeps going. Sometimes I can pump the throttle when it is trying to die and it will stay running for a little longer.

What am I missing? Leaving (hopefully) for a race Friday and need to figure this out. I figured replacing the parts would fix it but no luck so now down to the wire.

#2

Well it seems that when I hold the revs up I can hear it back fire or miss but not enough to probably notice on track. I tested the coil and it seemed good although the resistance from the center pin to the positive side was 7K ohms and the book said 5K ohms. But I seem to remember this before when I tested it.

Still need any and all ideas.

#3

Recall when I fastened a fuel pressure gauge to my windshield wiper? Do that so you can rule out fuel. Next time the engine starts to sputter, immed put eyeballs on the FP gauge and see if it’s all the sudden doing something flakey.

Replace engine harness. Also, carefully clean the round connector that goes to the injectors. All connectors get their V from a single wire so it is a possible culprit.

If the above doesn’t fix it, attack the critical electrical connections.

Pull the engine ground off at both ends, wire brush the contacting surfaces, put some copper or silver based anti-sieze on, and thread them back tight. Also do this at both connectors at the alternator, both conenctors at the battery, and everything that connects to the big 12V power point at the right firewall.

My F/A ratio gauge has proved to be a very valuable diagnostic tool. Buying and installing one would be too much of a distraction for this current effort, but consider it in the weeks that follow.

#4

I have watched a pressure gauge and volt meter while holding the throttle open by hand under the hood. No fluctuation before it dies. I will start inspecting the connections but this does not feel like a random thing. All runs good and then it is just off.

#5

With what you have replaced and the symptoms, my thoughts are than you have intake leaks or a bad engine harness. A smoke test will reveal any intake leaks. The only real diagnostic for the harness is to replace it.

#6

I just can’t wrap my head around how it can be a harness issue. It is like a switch is thrown and it turns off. If I hold the RPM up say around 2000 and when it start to die I can immediately open the throttle to say 90% it sometimes will stay running. I don’t think it is an intake leak but will check again. It runs to good when it runs. No rough idle or anything. I may have an extra engine harness somewhere. I guess this is the harness from the ECU out to the engine?

Keep the ideas coming.

#7

[quote=“ilateapex” post=64808]I just can’t wrap my head around how it can be a harness issue. It is like a switch is thrown and it turns off. If I hold the RPM up say around 2000 and when it start to die I can immediately open the throttle to say 90% it sometimes will stay running. I don’t think it is an intake leak but will check again. It runs to good when it runs. No rough idle or anything. I may have an extra engine harness somewhere. I guess this is the harness from the ECU out to the engine?

Keep the ideas coming.[/quote]
You need to be watching the FP gauge during one of those “starts to die” episodes where you catch it and it keep running. That will likely tell you if an FP hiccup, which could have a number of causes, it what is stopping the motor. Or is will let you rule out FP as a cause.

The signature scenario for an electrical problem is the intermittant scenario. Just because it’s a puzzle doesn’t make electrical less likely as a cause.

That being said, maybe I’m not understanding the symptoms correctly. I interpreted your post as “sometimes it will idle ok for a while, and other times I have to give it gas and keep it at 2krpm or it will die”. Is that correct? Or is it closer to “being able to idle is only an occasional fluke?”

Have you tried monkeying with the idle adjustment screw such that the car wants to idle faster, say 1500rpm?

I’m sure you already know this but the idle problems are usually vac leaks or the IAC valve. Does the IAC buzz at key-on? Vac leaks can be devilish. There’s some good DIY smoke generator ideas on the web. You just need a big metal can and a way to provide low pressure, just a couple psi, air. Or a neighbor that smokes, I suppose.

Welcome to: “Gee, wouldn’t Megasquirt logging be nice?”

#8

Take the cap off the big round diagnostic plug

Check all harness grounds and engine to chassis grounds

Have you tried another ECU?

Bridge the kill switch

put a chicken foot under the hood somewhere

Al

#9

Let me try to clarify. I can start the car fine. It will idle fine. After a minute or two it will die. There is no indication of a fuel problem based on watching the gauge. I also watch voltage between the lug on the firewall and the ground on the strut tower. No voltage issues there.

I can also start car, rev the engine and when it starts to die can sometimes get it to stay running. I can also start car, get running, take off and drive and once in 2nd gear and RPM’s up it will get me where I am going.

Since my first post I have added to the bait and switch list: Coil, clean engine ground at oil pan, clean power terminals on starter, clean injector plug, Inspect C101 (I think), did all the ECU plug checks in the Bentley.

It is as if something is getting interrupted and then coming back on. Injectors or ignition. When this first started happening at Nationals I just about did not make it onto the dyno at impound. The car kept dying and had to be restarted and then jumped. But when on the dyno it put down very good numbers and a smooth curve. I suspect that whatever is causing the problem that when it happens at 5000 RPM it just happens so fast it is not noticeable.

Al, I just installed a new heavyer duty kill switch and the problem is the same.

Ranger, I remember you talking about voltage to the injectors and their electronics. You ran a dedicated circuit or something?

Another thing, the Batt light is not on on the dash anymore. I pulled the cluster and the bulb is OK and the car started without the cluster in and the alternator started charging so I guess it is not needed.

#10

I am not comparing voltage from the big wire at the fire wall to the one feeding the ECU. The big on has 13.89 V and the little one has 13.61 V. It fluctuates when it is getting ready to die. I uncovered the fuseable link at the battery and it looks ok but could the soldier connections be corroding and causing a problem? I cleaned the ECU batt connection as well as the grounds on the strut tower. I was able to keep the car running longer with steady raised RPM. It would start to die and then take back off. Seems to be an improvement but may be in my head.

Also, it now looks like there is a slight dip in fuel pressure as it stumbles. I am going to replace the fuel filter just in case.

#11

Ah, more information…

12.6 on the wire feeding the DME is on the low side as compared to system voltage. Both lugs on the side feeding the kill switch and on the side feeding the car should have the same voltage. If the DME lead (small wire) drops much below 12.6v the DME may brown out. I think that figuring out why you see a difference (and fluctuations) there will cure the problem.

The alternator may also be a part of the problem. The bulb (or it’s bypass resistor in the cluster in very late production) is the source of exciter power for the alternator. Without exciter power the alternator may only minimally charge at high rpm. If the bulb is good start checking out the wiring between the alternator and cluster and check the fuses that feed the cluster.

#12

The fact that it seems to idle ok until it warms up a little caught my interest. The DME provides an rich mixture for the first couple minutes. This symptom points to vacuum leak.

Re. power to injectors. What I did was run a wire that bypassed the master power relay, a known problem child. This provides an alternate power source for a number of things to include the DME and injectors. I ran the MP relay wire to a switch on my dash. The purpose was to ensure that a flaky master power relay, or relay socket couldn’t cause me problems. Once the car started I flipped my switch, and on the cooldown lap I’d turn the switch off.

#13

we had similar problems with mike’s car a few years ago. As Al noted, we removed the jumper insert in the DME diagnostic cap and it fixed the problem. Can’t explain how or why.
Ed

#14

[quote=“jlevie” post=64815]Ah, more information…

12.6 on the wire feeding the DME is on the low side as compared to system voltage. Both lugs on the side feeding the kill switch and on the side feeding the car should have the same voltage. If the DME lead (small wire) drops much below 12.6v the DME may brown out. I think that figuring out why you see a difference (and fluctuations) there will cure the problem.

The alternator may also be a part of the problem. The bulb (or it’s bypass resistor in the cluster in very late production) is the source of exciter power for the alternator. Without exciter power the alternator may only minimally charge at high rpm. If the bulb is good start checking out the wiring between the alternator and cluster and check the fuses that feed the cluster.[/quote]

The voltages I am seeing are 13.8 and 13.6 It is around 12.5 until the exciter gets things going. I’ll check the wiring and fuse and see what I can find. The light used to be there and work (I think).

#15

[quote=“Ranger” post=64818]The fact that it seems to idle ok until it warms up a little caught my interest. The DME provides an rich mixture for the first couple minutes. This symptom points to vacuum leak.

Re. power to injectors. What I did was run a wire that bypassed the master power relay, a known problem child. This provides an alternate power source for a number of things to include the DME and injectors. I ran the MP relay wire to a switch on my dash. The purpose was to ensure that a flaky master power relay, or relay socket couldn’t cause me problems. Once the car started I flipped my switch, and on the cooldown lap I’d turn the switch off.[/quote]

It does not seem to matter if it is cold or warm. I have been able to get it warmed up to where the cold enrichment would not be in effect and it still does it.

#16

[quote=“edavidson” post=64819]we had similar problems with mike’s car a few years ago. As Al noted, we removed the jumper insert in the DME diagnostic cap and it fixed the problem. Can’t explain how or why.
Ed[/quote]

I’m not quite sure what jumper you are referring to. I believe the jumpers in the cap are jumping non used pins. Well maybe that is in the E30 M3, I remember checking it out before but I think it was the M3 I was working on.

#17

Well I changed the fuel filter and no help. I took the cap off the diagnostic plug and that did not help. I tried a smoke test of sort and found a crack in the valve cover and was hoping that was it but Replaced that and no help. Now the voltage is not coming up to 13.6 but I am afraid to rev to high so not to disturb the neighbor. Will get back on it tomorrow afternoon.

#18

[quote=“ilateapex” post=64822][quote=“Ranger” post=64818]The fact that it seems to idle ok until it warms up a little caught my interest. The DME provides an rich mixture for the first couple minutes. This symptom points to vacuum leak.

Re. power to injectors. What I did was run a wire that bypassed the master power relay, a known problem child. This provides an alternate power source for a number of things to include the DME and injectors. I ran the MP relay wire to a switch on my dash. The purpose was to ensure that a flaky master power relay, or relay socket couldn’t cause me problems. Once the car started I flipped my switch, and on the cooldown lap I’d turn the switch off.[/quote]

It does not seem to matter if it is cold or warm. I have been able to get it warmed up to where the cold enrichment would not be in effect and it still does it.[/quote]
We’re confusing each other. You said that the car starts, will idle for a couple minutes, and then the problem starts. I’m trying to point out the coincidence between “idles ok” and “cold enrichment”.

It’s hard to rule out anything at this point. I know that you tested FP with a guage and it showed good, but it’d be worth doing that test again just to double-check.

We can’t rule out vac leak because the nature of the leak could change with heat or vibration. Problems are diabolical.

I’d replace the engine harness and injector harness immed. Or just buy new ones.

#19

Mike, try these things:

Check the bolts to the vibration damper. If the damper wobbles the crank position sensor (CPS)gets bad info and it stumbles. Check/replace the CPS.

Replace the master kill switch or bypass it for testing at a DE.

If it is a later model, replace the wiring bundle that goes to the injectors.

RP

#20

Thanks Robert.

The problem has persisted through 2 different kill switches. CPS has been replaced and checked. I just did the timing belt and the problem happened before and after the change and the damper was installed tight and does not wobble. I will try the injector harness.

What do I do to get the batt warning light to work again?