1993 Fox engine stops running at random times

[3than]

I have a 1993 VW Fow that runs great. About once or twice a month it will be running just fine when all of a sudden the engine will stop running, a second later it will run causing the vehicle to jerk violently then the engine will die. When trying to start immediatly after this happens the engine will turnand sputter as if it wants to start but is being sufficated.
I have found that when this occurs I will undo the latches on the air filter compartment ,reach up into the air filter compartment housing and work a flap back and forth corrects the problem and the vehicle will run great until I need to do this agian.
Is something getting stuck? What should I replace? Is there something I can do to recreate his problem for a technician?

thanks
ethan

[noodle32]

You need a new Ignition Control Unit - I know someone that had a similar situation and everytime the car would warm up it would just die - replaced it and not only stayed on but worked like new! If that doesn't work you may need have your Mass Air Flow sensor (on top of the air filter) replaced - or your Idle Stabilizer Valve - but I would go w/ that ICU first - Hope this helps!

[3than]

Since correcting the problem involves me unclipping the air filter compartment and fiddling around with the flaps that are found inside of the air filter compartment should I start with the Mass Air Flow sensor first? It sound less expensive than the ICU

,Ethan

[Ely Mae]

what is an ignition control unit... I think I need the same exact thing.

[noodle32]

First I wanna say that this part can be found near the left side of the engine compartment near the cowl that hides the windshield wiper mosor (next to it not under it) but anyways what this does basically is ensure's that you have enough spark when you start up your car - usually when you know that you may need to have this part replaced is when your car kinda 'stumbles' to idle at times - (when it starts up with a lower than usual idle I'm saying) and it just feels kinda hesitant - what this does is it sends a signal to the hall sender basically telling it 'hey - I need more spark on the double!' and the hall sender will respond instantly by increasing the idle to its 'ideal' idle speed based on calculations made by the ECU based on temperature, pressure, air/fuel ratio, etc. some people don't realize that they even have an ICU and decide to buy the aftermarket MSD ignition control unit instead to ensure the best possible spark detonation at all times - from when the engine is started to when its being idled, accellerated/decellerated, and turned off again - this can also affect your gas mileage as well! (and we all know how important that stuff is to us all - well most of us at least Hope this helps! Just remember though I would recommend (for this car) that they do make ICU replacements OEM designed w/ or w/o heat sinks - and if you can find one w/ a heat sink I HIGHLY recommend it - it'll keep this part cool so that it lasts much longer - I mean with all the electricity and heat going through one little part I would definately recommend it Good luck!

[boschmann]

Originally Posted by Ely Mae

what is an ignition control unit... I think I need the same exact thing.

If you have a Fox the ICU or Hall efect ignition control unit would be located on the underside of the right side of the dash behind the glove box, near the larger engine control module. That is assuming you have a CIS or Digifant II Fox, Digifant I (California emmission) Foxes did not use an ICU. Usually when an ICU goes bad you lose all spark, but on rare occurances I have seen an ICU that will quit when hot, then after a minute will begin working again. It is usually simple to diagnose as there is no spark for the few minutes it is inoperative. However, even under this scenario, the Hall sender in the distributor should be checked also. Again, Hall senders in the distributor (and a bad wiring connector at the distributor) usually will just quit, but are just as rarely able to work intermittently when hot, causing loss of spark.

[noodle32]

I've been having this happen alot lately - it'll start fine when cold - but once it gets hot it takes well - alot longer - but i always turns over - just cranks for awhile - I appreciate the advice though !

[boschmann]

Originally Posted by noodle32

I've been having this happen alot lately - it'll start fine when cold - but once it gets hot it takes well - alot longer - but i always turns over - just cranks for awhile - I appreciate the advice though !

What year & vehicle are you talking about?

[noodle32]

1990 VW Fox

[boschmann]

You should have a CIS-E system. You need to check the fuel pressures, which is somewhat complicated & requires a special gauge set. The other thing to check is the engine coolant temperature sensor, it's on the coolant flange where the radiator hose connects to the cylinder head near the distributor. Using a multimeter you can test between the two pins. Resistance should be 2000-3000 Ohms cold, and decrease steadily to 250-350 Ohms at operating temperature.

[noodle32]

I was wondering though - should the fuel pressure regulator have fuel coming out of the port that goes into the manifold? Cause mine doesn't - it looks really old and kinda rusted up looking - I was under the impression that excess fuel was to be recycled through this part back into the manifold where it would be re-inserted back into the fuel tank? Sorry if I sound dumb just kinda misled here - but any help would be appreciated!

[boschmann]

For some reason in that last post I stated it didn't have a cold start valve, but it does. I deleted that to avoid confusing anyone. There are three lines on the regulator, if you loosen any of them fuel will come out. The one that comes out at the end returns fuel back to the tank, the large port on the side is the fuel into the regulator from the fuel distributor & the small one on the side I think is a feedback to the differential pressure regulator on the fuel distributor. As I stated any diagnosis of these components requires a special CIS fuel gauge set, I've seen them for around $100. Also, you would probably need a special wiring harness adapters for the differential pressure regulator. That is how you adjust mixture & check operation of various components (O2 sensor, potentiometer, etc...). A couple of other things I thought you could check yourself is to pull the cold start valve when the engine is hot & make sure it is not spraying when you crank the engine. You can also spray starting fluid around the base of the injectors to see if the seals are leaking, see if the engine RPM's change.

[noodle32]

I forgot to mention that I recently upgraded to a larger diameter intake tube I found at the junkyard - its about a half inch wider than the one I had on there - at first it had a hard time starting up but each time got harder and harder until it was nearly impossible to start after turning it off and letting it rest awhile - but after about 10 minutes or so I am able to start on the first crank everytime - my mechanic mentioned that because more air is now getting into the intake a time - the air/fuel mixture screw needs to be adjusted to recalibrate the correct ratio - says it'll cost about a hundred (being that I'm a regular customer) w/o any complications - so I hope that's the reason why so I don't have to worry about it anymore - I'm guessing it needs more air cause if I crank it long enough the engine smells as if its being flooded (and drains the battery quickly) but hopefully this is the solution I'm hoping will bring my car back to starting normally Thanks for the advice though!