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Odd problem - Engine shuts off at high boost for just an instant

crewchiefpro

Hard-core CEG'er
Joined
Feb 26, 2008
Messages
1,180
Location
Citra, FL and Peoria, IL
This one has me stumped and doesn't happen all the time.

If I accelerate fairly hard the engine shuts down for just an instant then continues on as if nothing happened. When this happens, the red light pops on the dashboard just like I turned the key off and turned it on again. The red light will go OUT an instant later, and the engine power returns to pull like a raped ape.

I verified this by driving down the road and shutting just the ignition part off with the key. When I shut off ignition the red light pops on. If I then turn the ignition back on ( but not try to start it ) the engine re-fires and the red light goes off.

I only get this on high boost ( over 12 lbs ) when accelerating quickly. If I bring up the boost slowly it never has an issue, all the way to 18 lbs if I have the nerve.

My guess is something in the wiring is being pulled by the engine torque movement. I had an issue with the injector harness plug where I could move it back and forth at idle and kill the engine. I repaired that connection and now I cannot force the problem at idle.

It is NOT a fuel related issue. Problem is in the ignition wiring somewhere. Since the red light goes out immediately after the engine looses power, it has to be torque related. Anyone know what can turn on the red light on the dash besides the key being turned out of the ignition cycle?

I bought a replacement wiring harness for the injectors, crank and cam sensors but have not installed it until I can determine exactly the problem. Guess I can get my son to ride with me while data logging and see if anything shows up.
 
My car does the same, if I shift hard from 1-2 or 2-3, cuts power for a split second, light comes on solid for 2-3 seconds then goes off.
I was assuming it was a wiring issue as well, maybe a bad ground somewhere.

PS, my car is not boosted, for reference.
 
I am no where near redline, this thing pulls so hard at 3800 it will scare you.

When I put the engine in additional grounds were put on as well. After winter is over then I will try to diagnose it. Don't drive it in winter anyway.
 
....sounds more like a power lead issue rather than a ground ..... as Beans said, altenator or even starter motor definitely high current circuit...... G
 
....sounds more like a power lead issue rather than a ground ..... as Beans said, altenator or even starter motor definitely high current circuit...... G

Radio stops playing but the headlights and dash lights stay on. I will go under the back side of the motor then check the starter lead and make sure the connections are right. I will examine the giant fuse connections also. It is tough to diagnose since it only does it under full load in lower gears.
 
Sounds like a broken wire. Does it do this when the engine is hot or anytime? Maybe you have a wire messing up when it gets warm enough...then the motor torquing over makes it an intermittent connection.
 
Sounds like a broken wire. Does it do this when the engine is hot or anytime? Maybe you have a wire messing up when it gets warm enough...then the motor torquing over makes it an intermittent connection.

I don't go into boost until it is at normal temperature. I am quite sure there is a wire issue, just not sure how to find it. When I return after winter is over then we will take the wiring apart and see if anything looks suspect. I think the problem is in the wiring near the ECU since I thought the engine idle changed when I grabbed the wiring and pushed it back and forth. Of course this only happened a few times and could not reproduce it again. I ran out of time to check into in this more thoroughly before I had to leave for the winter races.
 
could be one of the 3 multi pin plugs on the side of the rear cam cover. I have thin zip ties holding my plugs tightly clamped after a loose plug left me stranded .... G.
 
Not yet, it comes and goes. Thought I had tracked it down to the ecm connector and wiring but it still does it. Today it didn't have any problem in second but did on third gear. Then it was fine for about an hour until I tried to slowly move from a stop and it bucked once. Been fine ever since. Hard to replicate because a built turbo 3.0 will pull so much harder in 3rd gear than most Contours do in 1st, so I have to focus on driving it.

I think I will take the hood off and put a camera on several areas to see what is moving under full throttle.
 
Found the problem ( I think ). This is tough to find for sure since it is intermittent.

The main power cable from the battery in the trunk had been damaged and would intermittently touch ground. Found it near the rear tire as it went over the rear suspension. It was well protected in a plastic sheath but something must have kicked up and caused the damage to the cable. Anyway after removing the entire cable and stripping the plastic protector off of it I could see burn marks.

I am replacing it tonight so we will see shortly.

I will also add two 300 amp fuses to the battery cable.
 
Replaced cable and it seems to run perfectly now. Hard to tell since it rained earlier so all it does it spin the tires in any gear but 5th. No red light, no miss all the way up to 20 lbs of boost in 5th gear.

This car makes me chuckle every time I drive it.

UPDATE: Drove it today in dry conditions and it is officially fixed. This car is crazy when the boost goes over 15 lbs. in second and third.

Moral of the story, if you have a battery relocated to the trunk check the cable often for damage.
 
Found the problem ( I think ). This is tough to find for sure since it is intermittent.

The main power cable from the battery in the trunk had been damaged and would intermittently touch ground. Found it near the rear tire as it went over the rear suspension. It was well protected in a plastic sheath but something must have kicked up and caused the damage to the cable. Anyway after removing the entire cable and stripping the plastic protector off of it I could see burn marks.

I am replacing it tonight so we will see shortly.

I will also add two 300 amp fuses to the battery cable.
Hmm. I certainly am glad that you found the prob don. But i gotta ask why you have your cable running underneath the car, & not inside?
 
Hmm. I certainly am glad that you found the prob don. But i gotta ask why you have your cable running underneath the car, & not inside?


Good point. Actually I didn't do the original battery swap. When I bought the car the battery was already moved to the trunk. You are correct, I will probably move the cable inside as far as possible.
 
As a follow up to my problem with the motor shutting off under high boost. Here is a further update:

Turns out I had 2 problems. I replaced the positive cable from the trunk to under the hood and thought it had fixed it, but a few days later the problem came back. The weird thing is that I had a fuel smell as well. I could not find it anywhere. What I found is the motor moved so much under high boost that the main power lead connected to the 175 amp cable actually hit the fuel line on the body right behind the valve cover. I could not see anything obvious from up top.

When I removed the rear roll restrictor, started the car up and forced the motor back it touched the fuel line with the main cable and shut off the engine !!! It also caused a rub mark on the fuel line and I could see a microscopic pin hole and a small beam of fuel would come out. The fuel spray was so small you could not see it, only feel it and of course smell it. How it didn't cause a fire I have no idea. The main cable was worn through just enough to let it short to ground once it hit the fuel line. This mark on the main lead was so small I couldn't see it, but when it hit the fuel line it would pull back the insulation then pop back into place.

This means the motor moves about 3 inches under torque !!! The motor mounts are filled with 94 and still in good shape. I believe they are just not strong enough to stop 400 plus ft. lbs of torque. I will refill another one with a more solid mix and see if that helps.

I removed the fuel line, cut and aligned it in a different design. Then moved the main cable and covered it with thick rubber. Now I can move it all over and it won't contact anything.

I tested the car all day yesterday and am happy to report the beast is back again. It runs better than ever now that first and second are usable under boost. What I also found is that third though 5th gear is better because it would miss just a bit before and now is happy again.

So, those of you with turbo or supercharged cars check if it is possible for the main power lead going to the 175 amp fuse is able to touch your fuel line or anything else metal.
 
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