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The Case of the Dying Car

LeedomtoFreedom

New member
Joined
Oct 11, 2017
Location
Ingleside
Dear detectives,

My car has had an intermittent issue where while driving (idling or moving) the ignition seems to cut off and the car will roll to a stop. After several minutes of sitting, the car can be cranked and will start again.

I can hear the fuel pump and can feel fuel pressure in the line when the car loses ignition

When the car failed once, I tested for spark at the coil, no spark

The CPS, while fairly new, is a cheapy cheap China make.

I'm using LH2.4

Whatcha got.
 
Check for codes and see if it set the engine speed sensor code. I've had this sensor cause strange no starting intermittent stalling and never set a code. But it is good to check. See if it stalls when you move the wiring.
 
I had this happen on my 740 last summer (2.3 with Regina), and it turned out that there was a short in the harness side of the connector for the crank position sensor. I discovered that I could wiggle the wire around the connector and cause the engine to cut off as if you just turned off the ignition switch.
 
While thinking about this another intermittent came to mind. that is the ignition amp on the left inner fender. They can heat up and stop working. After cooling they work for awhile again. The connector corrodes too.
 
Sounds like an ignition power stage. You might even be able to save it you give it some new thermal paste. You can test it with a DVOM when it fails pretty easy, if you refer to the green books. Don’t buy the beck arnley part, get the Bosch.

Edit: just saw this was mentioned already as the ignition amp. Yeah they heat up and die when the thermal paste hardens and pulls away from the heat sink. I think they might have some sort of thermal overload, because I’ve had a few that were cured by giving it new thermal paste.
 
Update, gave it the wiggle test with no results. Haven't checked for codes yet.

I'm thinking about buying a CPS just for good measure, as it's something I want to replace anyway.

Because intermittent issues are the most difficult to tackle, how might I check the power stage without being on the road. As it consistently dies at the intersection of Higgens road and Roselle road, which is the busiest intersection in Illinois, not ideal for little checkups.

Is it the same process as thermal paste on a PC? Just pop it off, put a pea of paste, reinstall.
 
Update, gave it the wiggle test with no results. Haven't checked for codes yet.

I'm thinking about buying a CPS just for good measure, as it's something I want to replace anyway.

Because intermittent issues are the most difficult to tackle, how might I check the power stage without being on the road. As it consistently dies at the intersection of Higgens road and Roselle road, which is the busiest intersection in Illinois, not ideal for little checkups.

Is it the same process as thermal paste on a PC? Just pop it off, put a pea of paste, reinstall.



How check powerstage? LED test light to the input signal. It's a 5v square wave. Bulb test light to coil negative. That signal spikes to 400v!. If you have signal in, but nothing out==powerstage.



I haven't done much practice with a meter, but I'm sure you could use one. You can meter check the crank sensor resistance and see if it goes out of spec, but resistance checks aren't my favorite. You can also measure the output voltage of the crank sensor in AC voltage. That is also in my sig.


Or use an oscilloscope. I used one yesterday to look at the pulse width ground signal from the HVAC control module to the blower control module/resistor on a modern car.


EZK thread:

https://forums.tbforums.com/showthread.php?t=322395
 
Update, just swapped my alternator with a different, known good one, re-did the thermal paste on the power stage, and replaced the battery with a different but newer one that I had.
 
Update again, none of this fixed it, still dying in the road. Might bust out the parts cannon.

This time, it did it within 2-3 minutes of driving. revs fell flat, and I rolled it into a gas station.
 
Jumper your fuses (search to find out which ones) and make 100% sure your in-tank pump is working- listen for the buzz..
 
This seems like it will happen if you just sit parked and let the problem happen. The best time to troubleshoot is when the problem is happening. So try running the car parked in a place where you have access to your tools.

The no spark condition you describe just doesn't seem right to me. Because you then write that you feel fuel pressure. So with that in mind, the fuel wont flow till the computer thinks there is spark. For that to happen where you have fuel but no spark means it is somewhere in the ignition that isn't part of the circuits that the ezk would acknowledge a fail with a code. For example a engine speed sensor fail should/would give a code and the ezk would not make spark. Thus you have no fuel pressure either. But a bad coil wire or plug wire shorting out and causing a stall wouldn't be noticed by the ezk and you would have fuel pressure since the computer sees a rpm signal.

So try looking around make sure pins are good on the power stage connector. The coil should be checked with a resistance check. The connections cleaned and tightened. Also make sure the top of the coil isn't dirty. A dirty coil provides a short to the ignition so it may cause a stall or intermittent miss. If you have the coil wire with a right angle connector with a horizontal coil this can cause a short as the coil wire runs next to the strut tower and cause missing and stalling.
 
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