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Dan
Dan, Technician
Category: VW
Satisfied Customers: 21476
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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92 vw cabrio: floods..injectors pumping too much fuel into the system

Resolved Question:

92 vw cabrio. engine floods out because injectors pumping too much fuel into the system. how to fix?
Submitted: 5 years ago.
Category: VW
Expert:  Dan replied 5 years ago.

If your fuel injectors are putting out too much fuel, its is most likely caused by the fuel pressure regulator sine that what controls fuel pressure. Here are instructions to replace. Let me know if you have questions. Thanks

 

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Customer: replied 5 years ago.
Already replaced that part with another not new regulator, didnt help. Some history: Bought car with rusty cylinders due to head gasket leak. Total replacement engine installed. Now trying to start it. Have already replaced that part with one from old engine, made no difference. So much fuel goes into engine I can see liquid fuel leaking from crack in exhaust manifold. (I know i gotta fix that). I pulled all 4 plugs and cranked without fuel hooked up to clear cylinders. reinstall plugs, attach fuel line, start it. runs about 30 seconds, then stutters and dies. fuel starts leaking thru exhaust manifold crack. cant restart without pulling plugs to purge fuel again. is that part the -only- thing that regulate the pressure? might be possible both I have are bad. System has plenty of fuel pressure...when I go to bleed it off theres lots of pressure there.
Expert:  Dan replied 5 years ago.

You can start out with fuel pressure test so you can know if fuel pressure is the problem or if injector pulse is the prolem. If your return line is clogged, this could also cause high pressure. Also, if you have low compression or do not have good spark, the fuel will not burn up and could cause this problem. Compression should be 131 psi minimum. If low, squirt a drop of oil in cylinder and check again. Let me know if you have more questions. Thanks

 

Application/QualifierPressure 1 (PSI)Pressure 2 (PSI)Pressure 3 (PSI)
RangeNoteRangeNoteNote
Digijet, Digifant44.0Y01136.0Y012Y013
Y011: System pressure without vacuum (PSI).
Y012: System pressure with vacuum (PSI).
Y013: Residual system pressure (PSI).

Customer: replied 5 years ago.
I know theres a barb on the end of the fuel containing pipe. The barb has a removable screw to block it off. I would assume thats where you hook a pressure gauge to test the fuel pressure. I would like to leave this issue open for the moment. I'll go find a pressure gauge to test with. I need this car to run and this seems to be the last issue before we can try to drive it. I wish there was some way to continue this discussion offline until we get this resolved.
Expert:  Dan replied 5 years ago.

We can continue this discussion, just come back and reply to the question. Yes that is where you test the fuel pressure. If fuel pressure is too high regulator is problem. If fuel pressure is right, verify compression is good. If compression is good hte problem is the injector circuit, here is how to test. Let me know if you have questions. Thanks

 

Check Brown/Yellow wire from the PCM pin #12 to each of the fuel injectors is not shorted to ground. The fuel injectors are bank fired on this application so a short to ground in this wire will cause all 4 fuel injectors to open fully.

2. Remove or cut the Brown/Yellow wire at PCM pin #12 and crank the engine. If the fuel injectors are no longer held full open, the internal injector drive circuit in the PCM is shorted to ground. In this case, the PCM will need replacement.

3. If the PCM internal injector drive circuit is found faulty, be sure to verify the actual resistance of each fuel injector. 15 to 20 ohms resistance is normal. Injectors that show lower than normal resistance can stress the PCM internal injector drive circuit and cause a shorted condition.

Customer: replied 5 years ago.
During the test I did when I had the injectors out.....when I turned the key on, all 4 fired for about 3 seconds then shut off. Each one sprayed about 2 tablespoons of fuel. When I cranked the engine they fired again, but just about continuously. That almost sounds like the note you said about all 4 injectors being fully open. Serious thanks for quick answer.

The fuel injector cable has 2 wires as input. I took it apart on my old engine, that cable assembly. The 2 input wires split out to all 4 injectors. 2 wires to each injector.

I'm long time vw nut but new to cabriolet model. Any chance of a pcm diagram to know which wires are which? I think you're on to something with the ground idea.
Expert:  Dan replied 5 years ago.

Here is a wire diagram I pulled up. There VW diagrams are a little confusing. Let me know if you have questions. Thanks

 

graphic

Customer: replied 5 years ago.
Hooked up fuel pressure gauge. Registers 43/44/45 psi when cranking. The parts store also said theres a coolant temp switch that can affect how much fuel is being pumped...I'll switch that too. I changed out one of the fuel injectors with a substitute. The replacement sprayed just as much as the the original. As per your ideas, that leaves the pcm as the culprit. Any other ideas?
Expert:  Dan replied 5 years ago.
I really could not immagine the coolant temp sensor making that large of a difference. You can buy the pcm used from www.car-parts.com and have it shipped to you. Sort by price and you should be able to find one used. But considering the wiring is good, the injectors test out. It sounds like your pcm is the problem. Verify this by checking fuel pressure to make sure its not too high. IF fuel pressure is like it should be, replace the pcm. Let me know if you have questions. Thanks
Customer: replied 5 years ago.
As an interesting thing......I hook the power to the injectors and crank the car. Does not start. Disconnect the injector power and crank the car. Car starts and runs until the fuel runs out. Does this jive with the current problem idea? Since there is no power, the level of fuel goes down allowing the car to run until it runs out. Thanks for the hint on the pcm...it was close to $300 when I checked at the parts store. Pass me some ideas one more time on this comment and I'll close this out with an accept and thanks.
Expert:  Dan replied 5 years ago.
The injectors have power at all times and are controlled by the pcm sending ground to each one. But considering it ran when you disconnected the injectors does not make sense. Using a voltmeter check both connectors at each injector. They should all have constant power and no ground since the pcm controlls ground. If any of them have ground you have a wiring short. If they dont have ground, pcm is problem. I"m about to leave for a few hours, so if you have something else to ask I'll get back to you later. Thanks
Customer: replied 5 years ago.
Just to clarify, with the injector power disconnected, it does not immediately jump to life. Has to crank 5 or 6 revolutions until the level of fuel in the cylinders gets down to a level able to burn. The engine then runs until the amount of fuel already in the cylinders runs out. When I hook up the injector power again, it then pumps so much fuel in, it immediatly floods, thus no start. Disconnecting the power cuts off the additional fuel and lets it burn what it already has. THANKS. I'll keep playing with this. I'll do the ground test and let you know.
Customer: replied 5 years ago.
I hooked up a second fuel injector wiring harness I had into the fuel injector power lines.
Key switch in off position and battery hooked up. Set tester to continuity setting.
I touched negative to battery (-). I touched positive to one of the fuel injector individual wire. I was able to get continuity on 1 wire in each pair to ground. For instance, holding the individual fuel injector wire plastic housing, the left wire showed continuity to ground. The right wire did not. Tested for dc volts and got .5 volts dc on meter. If I didn't test this right please let me know
Expert:  Dan replied 5 years ago.

You tested right. You can unplug the pcm and do the same tests on the pcm control side. You should not have any ground, if so, wire is bad. If no ground replace pcm. Let me know if you have questions. Thanks

Customer: replied 5 years ago.
Haven't tested ground at pcm side yet..but did this.

plug injector power wire
crank, engine doesn't start due to flooding
remove power wire
crank, after about 5 revs, engine starts and runs 10-15 seconds due to overfueling when plugged in.
engine starts to die.
plug injector power wire for 1-2 seconds, then remove.
engine revs up again since has huge slug of fuel
engine runs 10-15 seconds
engine starts to die
plug injector power wire for 1-2 seconds, then remove.
engine revs up again since has huge slug of fuel
repeat this.

Was able to keep engine running 2 to 3 minutes this way.
So thats pretty definite the engine can run with less fuel being dumped into
the system. The fuel injection power wires run up into the wire harness. As far as I can trace them they appear ok. I may have to cut the wrapping off the harness to follow them all the way back to the pcm and/or check make sure there are no breaks or grounds on the way.
On this car, there is a box on the drivers side right in what I would call the rain tray, outside of the car.
It has a large wire plug on the passengers side of the box. I'm guessing this is the pcm because of the wire bundle. Can you confirm?
Expert:  Dan replied 5 years ago.
I agree it is the pcm, but before you buy a pcm make sure fuel pressure isnt high. If fuel pressure is around normal it is the pcm. If fuel pressure is high, a clogged return hose or fuel pressure regulator has caused problems. Let me know if you have questions. Thanks
Dan, Technician
Category: VW
Satisfied Customers: 21476
Experience: Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
Dan and 7 other VW Specialists are ready to help you
Customer: replied 5 years ago.
As per previous answer, a fuel pressure gauge shows about 40 to 45 psi when cranking.
Sooo...the pressure falls in the range that you said it should.

I'll be on the pcm hunt. If you're interested in any personal follow up, I'mCustomer@ hotmail.com

I'd be glad to let you know how this turns out if you care to hear.

Thanks for your help.
Customer: replied 4 years ago.
Replaced pcm with used unit...car starts and runs like a dream.

Ty.
Expert:  Dan replied 4 years ago.
Thats good to hear......Thats what we both thought it was but its always good to make 100% sure thats the last possible problem. I'm happy it worked out, thanks.

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