car shut down on highway, then later started back up,help

bb · 07-19-2003, 09:00 AM

I was taking my car out today and had a problem that I have never had on this car. I just got it back on the road after doing some work (exhaust, new fuel injectors,headers...) It is a 2.7 with CIS.
Now for the problem:
I was running on the highway, not really pushin the car, but driving it about 70mph. All of a sudden the car shuts down. It is popping and backfiring real loud(sounded like gunshots). I pulled it off the road and it would not fire at all. I called the tow truck and waited.
Just for giggles I tried to start it about 15 minutes after it had shut off. And it started right up and ran perfect. I cancelled the tow truck and drove it home on the backroads slowly. But all the way home, again , it seemed to run perfect.

What could this be??
Oscar

350HP930 · 09:22 AM

The most likely cause is probably the ignition, followed by the possibility of a CIS failure.

The backfiring would be an indicator that you had fuel but intermittant ignition which is the reason it is my primary guess.

bb · 07-19-2003, 01:49 PM

but what would cause it to run good again once it cooled off?

thanks

Ruben911 · Ruben911's Garage

Oscar, same thing happened to me although not at such a high speed and it ended up being the fuel pump. My car would shut off and then after I waited for the car to cool down a bit it started back up again. As long as the engine did not get too hot the car would work fine with the weak pump. Is your fuel pump the original pump or has it been replaced lately. If it is original, then it may be at the end of it's life. However, you should check easy things first, like ignition.

Ruben

350HP930 · 07-19-2003, 02:34 PM

A dieing CDI box, coil or corroded wiring can be pushed past their limits by things like temperatures and high speed driving.

I have had to deal with both a fuel pump relay failure and a CDI box failure.

A fuel pump failure would most likely just shut the car down clean while an intermittant spark is likely to cause backfires when the unburned fuel goes into the exhaust.

toolman · toolman's Garage

It is probably the fuel pump since it worked fine after it cooled off. The motor in the pump gets hot and quits, then cools off and works again. I have had this problem in a few different cars.

350HP930 · 07-20-2003, 06:29 AM

My car has two new fuel pumps (and a lot of other new CIS components) it didn't need cause the PO took it to a mechanic that sold him on that idea when it had nothing more than a wiring problem.

Cost for me to fix the problem; $0 and my time. Cost to the PO for a lot of stuff he didn't need; over $1,500.

Take my word on this, if the car was backfiring its a likely sign of intermittent spark. Its kind of hard for your engine to create backfires that sound like shotgun blasts when your engine is getting no fuel. Fuel pump failure is just like running out of gas, its a loss of power situation.

While this is not a 100% sure thing its pretty likely. Its also a lot easier to pull your coil wire and check for spark the next time this happens than it is to check your fuel pressure.

RoninLB · 07-20-2003, 07:36 AM

Quote:

Originally posted by bb
I just got it back on the road after doing some work (exhaust, new fuel injectors,headers...)

Hey Oscar..
perhaps you were checking out the dizzy wires , etc and disturbed the dizzy trigger wire that's close to the engine case.. a touch and feel can push a terminal in close contact with the case.. just an unusual thing that can happen..........Ron

jbryant · 07-20-2003, 07:50 AM

Check your battery terminals. I had this exact problem last week and it was a neg. ground.

baratta930 · 07-20-2003, 12:51 PM

I would check the fuse for the fuel pump as well. My 930 did the same thing infrequently for the first 2 years I owned it, and I could never find the problem, then one day I noticed that the fuse was corroded and changed it (and cleaned up the posts), and it hasn't happened since (2 years).

Hope this helps ...

Jim Sims · 07-20-2003, 05:58 PM

If your car still has points check their condition (loose, burned contacts, etc.) and dwell (point gap). Also, check for the small flexible braided wire that connects the point mount plate. Check for loose distributor cap/rotor. Jim

rick conrath · 07-20-2003, 06:10 PM

I just posted a similar answer to another post. Check the connection at the main grounding stud from the rear engine harness. With time corrosion will form on the brass connection rings and cause a severe voltage drop. It gets worse as the engine warms. The last time I had this failure, the car would run and then just die under power. Lots of backfiring, complete loss of power as if you had turned off the ignition switch. Voltage going to the CD box with the key on would drop from 12 volts to .2 volts only after 5-10 minutes. I cleaned up the connections and have not had a problem since. I was not as lucky...the tow truck showed up before I could get it started. My car started when I got it back home in the driveway.
Rick
'78 930

john70t · 07-20-2003, 09:16 PM

The backfiring sounds like plenty of gas igniting in the hot exhaust headers so ignition would be the first thing to check(check strong gasoline smell at tailpipe and wiring).
The pump should make a little noise if it's running correctly.

bb · 07-21-2003, 08:50 AM

When I stopped the pump still made the high pitch sound but the car would not run.

Jim Sims · 07-21-2003, 08:54 AM

It likely isn't the fuel pump or fuel system. Check your ignition system; start with the points if the system still uses them. Jim

rick conrath · 07-21-2003, 09:33 AM

Check your connections and engine ground.
Rick
'78 930