motor dies

[molly]

After years of trouble free use,my 84 carrera has developed a fault. It starts fine but as i drive away from a stop,by the time I'm in second gear and the revs are about 3000 it just quits.It will restart and I can drive on till the revs hit 3000 and it will quit again.I have changed the plugs,same thing.I will change fuel filter next.I was wondering if there is a fuel injection part that exhibits this trait when faulty.Thanks for any help you can give.

[DRACO A5OG]

Hmmm. have you checked your AFM, potentiometer, if the tension sweeping arm that glides over the potentiometer membrane is worn down to the point there is no contact, your car will die ergo, no signal.

Search the AFM service a 944 guy was the OP.

Jim

[molly]

AFM...air fuel meter?I was just reading about the cylinder head temp sensor?

[DRACO A5OG]

The CHTS usually affects the hot/cold start issues.

It could be the ref/speed sensors. Before tearing into the Air Flow Meter, check the OHMs on all the sensors, CHTS, REF/SPEED.

It is only when you route it runs up to 3K RPMs tells me the there is a dead spot on the poteniometer swipe, the 944 service shows how to see on a DVM what the voltages are when the arm moves. In fact you will notice the wear is deeper at the 2.5-3.5K RPM range. The fix is a delicate re-tension of the copper arm, do not do too much it will cause a more severe wear, once the membrane is broken, you have to buy a new AFM

[DRACO A5OG]

Heck, check the Dizzy Rotor for slop, If the shims are worn off, it can cause a miss fire, but damn to die totally is back to AFM.

[kidrock]

I'm curious to find out if the motor dies at 3K in neutral.

[molly]

Does not do it wile sitting stationary,it seems that it must be under lode.It does not do it every time but driving briskly I wont make it a block.The car is not warmed up,maybe I should try letting it warm-up and then try.

[molly]

Does not do it wile sitting stationary,it seems that it must be under lode.It does not do it every time but driving briskly I wont make it a block.The car is not warmed up,maybe I should try letting it warm-up and then try.

[DRACO A5OG]

Can to take help and video the symptoms?

While coasting in neutral try Stone's test.

Check the ohms those sensors.

Next would be to check theme solder joints, but that is the last thing.

[molly]

I will work on those things tomorrow,its dark now.Thanks for your help.

[molly]

Is the AFM the part between the air filter and the elbow into the intake manifold?

[Quicksilver]

Originally Posted by molly

Is the AFM the part between the air filter and the elbow into the intake manifold?

Yup that is it.

The 'wiper mod/adjustment' that Draco mentioned is a good preventative maintenance item for one of these cars with a bunch of miles so it is a good idea anyway.

Describe the failure more...
How hard does it cut off? Is it like a light switch?
Does it stay completely dead until you retry starting it or is it more of a 'not running enough to continue'?

The fact that it seems to be load based would seem to say that when the air/fuel demands reach a certain point the game is over. That could be the AFM as the air is part of it but it could be fuel.
A clogged filter or a weak pump could make it dry up past a certain level of load/rpm.

I've heard of reference sensors causing it to cut off past a certain RPM. So that will bear checking.

All of these things are testable so don't jump in and start replacing things. (Well if you know the fuel filter is old you might as well do it anyway.)
- The AFM can be tested with a multi meter.
- Testing fuel flow requires some care cause open gasoline can be dangerous.
- Testing fuel pressure requires an odd fitting and a gauge (preferably with a long enough hose you can see it while driving).
- Testing the reference sensors can partly be done with a multimeter but a thorough requires an oscilloscope. (surprisingly easy to do.)

Work your way starting with the simpler ones and you will find it.

[molly]

It does cut out like a light switch.
It does it stay completely dead until you restart it and it always restarts.Ive never changed the fuel filter,I know I should have.Could be simple fuel starvation. It does run better and has improved idle with new plugs.

[DRACO A5OG]

Good grief, yes no matter what change that filter. It can be pita but worth it.

[molly]

Still starting and running then stops.Heres what I have done.

I checked the ground,changed the fuel pump fuse,put in new fuel pump,checked fuel pressure.40 psi when running then when motor stops jumps up to 115 psi,then pump stops, psi bleeds down to 0 psi.

I then replaced the relay under the seat,when I put my hand on it and key to run I feel one click,start car,car stops I feel another click I turn key off.

I replaced the cyl head temp with new 2 wire one,then I replaced one of the flywheel impulse senders and tried to start,same thing.swaped new impulse sender with other one,same.

Swapped coil for another good coil,same.I removed the car alarm,same.

What are the two relay looking things on left side of motor under cover for.So the current situation is I can start the car and it will run for 10 to 30 sec.and stop as if the key was turned off.Ignition switch?Motronic box?

[molly]

I also have a new cap and rotor and I back dated the heater,and put on a test pipe.

[robhamster]

Check the solder joints inside the DME box. You can search the forum for the best techniques. A magnifying glass is essential. I have an '84 that displayed similar symptoms about 7 years ago and it turned out to be bad solder joints. A simple hit with a solder iron to remelt is all that is needed.

[molly]

I just finished checking the solder joints inside the DME box and all looks good,got it all together and same thing. would start run 10 to 30 sec and shuts off.rechecked all grounds and polished them.I can feel the relay under the seat working like it should.

Something is shutting it off.I'm totally stumped.I'm about to roll it out of the garage and light it up.This my other air cooled car,much simpler

[rick-l]

Originally Posted by molly

40 psi when running then when motor stops jumps up to 115 psi,then pump stops, psi bleeds down to 0 psi.

Does this sound right?

[Tippy]

Someone else had this same issue and the FPR (fuel press reg) was sticking. You found your problem!