100mph to barely running instantly

raccaro · 05-23-2006, 06:51 PM

Here's the quiz. How could my 74' 2.0 be running perfectly one second and then have me stopped on the highway with a dead engine? Here's a brief history. The car had a consistent misfire with occassional good running in between. It also got to a point where it wouldn't rev above 3200rpm. Pretty frustrating trying to accelerate safely onto the highway. After checking my fuel supply system and resetting the fuel pressure(all to spec) I dove into the ignition system. I removed the distributor, changed and set the points, changed and checked the trigger points with an ohm meter, reinstalled and set the timing to specs. The car finally ran like I remembered with out a hint of a misfire and revving as high as I wanted. As I headed home from work a couple hours later I noticed some slight misfires or shudders but it kept running. I accelerated onto the highway and it pulled cleanly to 100mph and then as quickly went dead. After coasting off the highway I checked the wiring and everything looked good. It started and misfired for a few minutes and then started running like nothing ever happened. A few miles later I can barely keep it running. I rev the engine a few times, it comes up to speed and then drives perfectly the rest of the way home. I guess the trick question is what component or system can operate perfectly one second and lousy the next without simply failing altogether? Any ideas would help as I running out of ideas. Thanks

h16 · 05-23-2006, 07:19 PM

In case it's of any value ... when I was a youngster in mid-70's, I had intermittent cutout in my 71. In desperation I took it to the local dealer (serious desperation) who determined that I had oil in the lower-end of the distributor, which caused the FI timing/switching system to balk. I am not sure how they diagnosed it, but they solved my problem and got my rig to run reliably. The symptoms were that it would run, then just cut out. I don't recall missing; it was all-or-nothing.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Sounds like an electrical problem of some kind. I had a bad fuel pump wire once that would kill the motor dead while driving. Usually I could "bump start" it as it was coasting after it died, and it would come back. Took quite a while to chase that one down, though...

Keep checking the electrical stuff. Loose or broken wires can cause all sorts of weird intermittent problems. Try wiggling different wires while the engine is running and see if any one in particular will kill it.

Also check things like the battery connections. And, of course, your grounds.

--DD

pbanders · pbanders's Garage

Agree with Dave, probably electrical. I've had the exact same fuel pump problem he mentioned, check the connection from the harness to the pump for corrosion. Dizzy problems, loose connectors, etc.

John Rogers · 05-24-2006, 11:35 AM

trigger points.

hardflex · 05-25-2006, 05:06 AM

i had trouble with the fuse for the fuel pump on the relay board. The contact surfaces were dirty, so the connection intermittent. Connection=fuel pressure, no connection= it dies.

Cheap fix though, just clean the surfaces with steel wool or a wire brush.

tod914 · 05-25-2006, 08:01 PM

My 75 had the ECU go on it, simular problems like you mention. Maybe once you get all your grounds and contacts clean you can try swapping components with some good known ones if you have a fellow teener in the area??

hardflex · 05-26-2006, 03:37 AM

BTW, you can tell if it's an ignition problem or fuel system problem by watching the tachometer. If the points are working as they should the tach should read the proper RPM's, If it reads zero while the engine's still spinning, it's an ignition problem.

spoke · 05-26-2006, 03:43 AM

When this event happens, does your tach jump or fall to zero?

I had the strangest engine cut-out issue. Sometime would die when driving, sometimes wouldn't start. Turns out the wire for the tach which goes on the coil was shorting out in the wire bundle across the engine. I found it in frustration when I pulled all wires on the coil and started re-connecting one at a time. Engine ran good until I replaced the tach wire, then died. Probably not your issue but something to check.

Good luck,
Spoke

3D914 · 3D914's Garage

raccaro,

Another suspect problem is the Head Temp Sensor. The sensor often comes with a shrink tube over the end of the sensor where the wire is connected. I had these in the past where the wire was almost completely broken, but held together by the tubing. It would static test fine, and even run fine, but with intermittent drop out.

Good luck.

calbrat · 06-23-2006, 09:03 PM

When I got my car 6 or so years back, it always did this sort of thing and I determined that it had to do with fuses, since there were little packs of fuses all over the car but would it was only popping fuses once in a while.

I had someone put a new stereo in for me and he noticed all the ignition leads were all melted from the steering column towards where ever they made their way toward the engine. We replaced these and there hasn't been one problem since. Gotta remember these cars are 30 plus years old and the wiring can get weird.