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91 VW Jetta Diesel-Help!

I’ve had this Jetta Diesel for about 2 years, and generally it’s been a pretty good car. Here’s what’s going on with it now: When driving on the highway, all is going well until I come upon even a slight incline, at which point the acceleration starts to go, and even though I’m pushing hard on the gas pedal, the speed starts dropping to about 40mph. Then, sometimes, as this is happening, the engine totally shuts off, the battery light goes on, and I have to pull over on the side. If I turn the engine off, wait a minute or two, it starts with a little chugging. I can then drive it a couple miles, before it shuts off again, this time while slowing down and braking when taking an exit. Same thing- engine dies and battery light goes on.

We’ve replaced the fuel valve and the low pressure fuel injector pump. Still same problem.

Any ideas, please?

How many miles on the engine? Have you changed the fuel filter?

I would also suggest a compression check. I forget what is normal compression (it is a lot higher than in a gasoline car) and requires a special tester for the higher pressures. What kind of mileage are you getting?

Sorry I will be off line for a while, so if you respond someone else will have to answer.

There are 185,000 miles on it. And the fuel filter has been changed.

We get great mileage. 45-50 mpg highway. Don’t know if there has been a compression test done. Do you think there is any possibility that this could be a fuse failure?

No chance on the fuse. It’s time to have an diesel injection lab check out the injection pump. Nothing lasts forever…

You may have more than one problem.
Lack of power could point to low compression as Mr. Meehan says. This requires a special diesel compression tester and figures should be up in the 500-600 PSI range for a normal engine; low 400s means problems.

Injector pump timing being off could also cause a loss of power.

The part where it shuts completely off for a while COULD point to an intermittent electrical fault in the fuel shut solenoid circuit.

The battery light should light if the engine stops; that is normal. By fuel valve, do you mean fuel shutoff solenoid? There is no other fuel valve. Also there is no low pressure fuel injector pump in a VW diesel except the one internal to the injection pump. This repair requires a Bosch injection pump specialist; most mechanics can’t do VW diesel fuel injection pump rebuilds or repairs.

Regarding low compression, a VW diesel can run quite well with compression less than specified but starting can be a problem with low compression.
I can only suspect a leak in your fuel line that is allowing air into the fuel line from the tank. Diesel fuel is drawn from the tank by the vane (low pressure) pump inside the injection pump on the engine and a small leak in the line will draw in air; not good at all for diesel performance.

I suggest that you post your question on See Forums, Technical and then TDI and Diesel forum. There is plenty of experience there with VW diesels.

how about air filter? try either reinstall or replace fuel filter to correct connection that keep air out, sometimes air goes in fuel filter that cause what you described. let me know the results!

Yes my understanding is that he replaced the fuel shutoff solenoid. He also installed a after market pump and tied into the power wire on the injector pump to fix the low pressure fuel injector pump.

None of this fixed the problem.

Any possibility that replacing the Relay 109 could help? Read about it on another forum. I know so little though, that maybe my car doesn’t even have a Relay 109???

You misunderstand me a bit in regards to the fuel shut off solenoid. I’m not saying the solenoid is or was bad; just that there could be an electrical problem in the car that causes a lack of power to keep the solenoid working.

Once a diesel is running it is impossible to shut it off so that is the purpose of the solenoid; to cut off fuel flow and stop the engine. If one has an electrical glitch (relay, igniton switch, fuse block, misc. wire connector, etc.) then it’s possible for the engine to shut off intermittently when this problem occurs.

The shut off solenoid, located on the injection pump, without 12 volts applied will instantly shut down the engine completely. In the unlikely event that the solenoid is receiving rapidly intermittent power, it may be possible to lose engine power as described but I have never heard of such a situation. I can’t imagine how a hill could affect this.

To establish or put to rest this possiblity, I suggest that you run a single temporary wire with a ring lug crimped and soldered to one end mounted to the stop solenoid power wire terminal; run the wire in an expeditious manner to a cheap, small 12 volt lamp with lampholder inside the cab and ground the far end of the wire to the cigar lighter socket or to the ignition key. The lamp should be on steady at all times when the ignition key is on and, of course, when the engine is running.

There is an outside possibility that the auxilary fuel pump, if mounted under the hood is still sucking air from a leak in the fuel line back to the tank. Check if your car has the water separator underneath the car near the rear right passenger seat. These may have been gone by 01. If it is there, it can be safely removed with fuel line substituted if it is the source of an air leak. Look for fuel wetness.

I’m not implying that a hill will cause the fuel shut off solenond to become inoperative. That is why on my first post I suggested that there may be 2 separate problems with this car; one involving lack of power and the other a complete shutdown.

I would also point out that a timing belt change can affect the injection pump timing a lot even if everything is reassembled right on the money.
This is also why a diesel belt change should always have the pump timing checked as part of the procedure.

1991 is most certainly not a TDI; still an IDI. TDIClub site does not cater to IDI.

To the OP, you did not mention turbo. If your car has a turbo, that could be a factor.

Hi - I drive an 84 MB 300D that does the same thing when either of the two fuel filters is clogged… OR the in-tank fuel strainer is clogged with sediment or algae (usually the last thing people suspect). An easy test would be to blow out the fuel line backwards from the engine compartment with compressed air (you’ll have to bleed the lines again to get the air out of course afterwards) but if the tank screen is loaded up it will disperse and the car will feel like it has new-found horsepower at least until the dislodged junk recoats the screen and/or filters again. Wouldn’t hurt to just have the car jacked up, drain the tank and have the tank and screen cleaned too. Not sure where you live but if you’re in a cold area you need all the fuel flow you can get as the fuel thickens in winter. Good luck!

Sure sounds like a fuel starvation issue, something’s plugged up. If you want to keep this old VW going, you might consider getting the Bentley manual: