Strange problem on 83N/A

[nathan944]

I drove my car today because it was nice here and it did great all day, until tonight. I started to notice that it would "miss" or jolt a tiny bit every so often but not much at all. It kept getting worse as the night went on and finally started to buck violently upon acceleration at random times. I decided to take the car home and as I was getting off at the interstate exit the rpms dropped and then died. I was able to coast to a gas station. There I tried to start it again a few times and nothing but starter, no attempt to fire at all. I called a tow truck and was waitng for it when I decided to try to start it agian and it fired right up. (this was about 30 minutes after it died.) I was able to drive it home, with the same miss/jolt/buck symptoms. It is now in my garage waiting for you guys to tell me how to fix it.

ALSO a few things that may or may not have anything to do with this.

1. I ran the gas tank pretty low today (1/8 tank maybe), I try not to do this but I did this time.
2. I spayed down the motor early this morning to clean it up a little, but I took great care not to spray any electricals. It also ran fine all day long until the problem started tonight (i do this routinely.

Thanks
Nathan

[AznDrgn]

check the obvious things, cap, rotor, wires, and plugs.

[ae1969]

That sounds like a nasty intake leak.

Take a look at that J-boot for rips.........also all the hoses going to the intake.

[drew1]

fuel filter?

[DannoXYZ]

Check all your intake-hoses and clamps. Sounds like you've got a big leak somewhere. What happens is air flows past your AFM first and gets measured. Then if it leaks out somewhere along the way because of a loose hose clamp or a rip in one of the rubber intake-hoses, that measured air escapes. However, the DME computer THINKS more air is flowing into the engine than actual and meters appropriate amounts of fuel. But you'll end up with too much fuel and results in stumbling (because of the escaping air doesn't flow into engine).

[944 Ecology]

Originally posted by DannoXYZ
Check all your intake-hoses and clamps. Sounds like you've got a big leak somewhere. What happens is air flows past your AFM first and gets measured. Then if it leaks out somewhere along the way because of a loose hose clamp or a rip in one of the rubber intake-hoses, that measured air escapes. However, the DME computer THINKS more air is flowing into the engine than actual and meters appropriate amounts of fuel. But you'll end up with too much fuel and results in stumbling (because of the escaping air doesn't flow into engine).

Actually, Danno, methinks you have it backwards...

A leak between the AFM and the intake manifold causes the DME to think that it is flowing less air than actual and is making the engine run lean. At least , that's the way it is on an 83 944 (the original post).

OTOH, if you are thinking about a turbo car, a leak between the turbo and the intake manifold will cause a rich running condition under boost conditions.

gb

[nathan944]

Thanks for the replies. I just replaced the fuel filter about a month ago so i think i can rule that out. Ill check the plugs/wires/cap today.

[SoCal Driver]

You can't spray down the engine with out getting some of the electricals wet. Start pulling connectors and dry them out.

[Britwrench]

Take the ignition wires off the plugs and check for water left around the plugs. Also make sure the fuel pump relay is new.

You might also want to check the fuel pressure as too high pressure, due to fuel regulator failure, can cause similar problems although usually it's so bad the engine won't run.

There are a number of faults that can cause the problem you have, you are going to have to do some proper logical diagnosis. Hope you have a workshop manual.

[nathan944]

If it was due to water somewhere is it still possible for the car to run great for 40+ miles, and then start acting up later?

[DannoXYZ]

George, you're correct. A leak between the AFM and manifold would cause extra air to get sucked in on both an NA and a Turbo off-boost. Under boost, the Turbo would lose air. Either way a too-lean or too-rich mixture will cause drivability issues.

[Macfreak007]

nathan, take off the distributor cap, and spray it out with compressed air, this will dry it all out. It is possible this could cause the problem, lots of stuff to check... only spray down your engine when you REALLY REALLY need to, these cars do not like it!

[nathan944]

Ok, changed spark plugs (they were pretty nasty) and drove. It ran as smooth as glass. Carl I also cleaned out the distro cap. I asume either the issue wass the spark plugs, and/or moisture somewhere which must have dried uo on its own. The car seems to be fine, lets hope it stays that way

[Macfreak007]

Yup, I am betting thats what happened, whenever we used to wash cars at the shop I worked at, we would always have to blow out the distributor caps of certain cars that we washed the motors off on. Water finds its way in there no matter what! glad you got it!

[DannoXYZ]

The other area that water causes problems is the connector at the back for the speed & ref. sensors. They aren't water-proof and shorts out the low-level signals. I usually disconnect them and blow-dry both ends and re-assemble.