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4000Q starts rubs for 20 seconds and dies

4000Q starts rubs for 20 seconds and dies

 
Old 05-28-2018, 11:25 AM
  #1  
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Default 4000Q starts rubs for 20 seconds and dies

just bought this car yesterday after searching for years and had to trailer home due to it not wanting to run. I have good spark and compression hence Iím thinking some fuel issue.
It will crank and fire once running for about 20 seconds and then die out. After that she will not fire again just spit and sputter. When you turn key pump primes 7 out of 10 times and the time it runs pump continually runs.

I dont have a manual for it yet, can anyone tell me what tells the pump to run ? Iíve cleaned all grounds and checked for massive vacuum leaks so Iím thinking it has to be that pump not supplying fuel.

Any help is much appreciated!
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Old 05-29-2018, 08:38 PM
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The fuel pump runs because of the hall sender in the distributor. I guess the theory is that if the engine dies it'll shut the pump off. However, it does make it difficult to diagnose a fuel issue with that in the mix. For diagnostics purposes, I would remove the fuel pump relay (#10) and jump the slots with a piece of wire. Here's a diagram for that:



If the fuel pump runs, great. If the car starts and stays running with it like this then you have a result. There are other things to check out, but that's where I would start and it's the simplest.

BTW, the fuel pump relay is what causes the pump to prime. There are some relays that don't prime and some that do. The fact that yours is intermittent may mean there are some bad connections inside it, although they can be intermittent in priming but be perfectly good. We're not talking about advanced technology here. If you open it up you'll be able to see if there are any crack solder joints, which could be your non-running problem.

-Rog
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Old 06-05-2018, 04:34 PM
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Default No dice yet

So Iíve jumped the fuel pump relay and you hear it running but wonít run. Iíve pulled number one plug to test for spark and I have great spark. I had thought maybe something in the ignition switch it self (previous owner put a vw switch in) but it does start every now and then and run for a thirty seconds to a minute.

I also changed the fuel distrubutor actuator cause cause I know that controls lean/rich and figured if that had gone car wonít run either, but no luck there.
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Old 06-05-2018, 05:52 PM
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Okay, so what I would do next is take the air intake boot off so you'll be able to get to the air meter. Then pull your injectors (I know, not a super fun job) and stick each one in a bottle. Long hose pliers are really helpful to pull them and also to reseat them when you're done. Jump your fuel pump so it runs continuously and lift the air meter flap. A magnet is useful to give yourself a handle. Mainly you'll be checking to see that the injectors all spray, spray well, and that the amount in the bottles are all the same.

I'm kind of suspicious of the distributor. You're getting good spark when you test it but intermittent problems are like that, they work when you test them but still give problems. That would also be giving a no-fuel situation.

Did the car sit for awhile? If so, did they say why?

-Rog
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Old 06-06-2018, 05:02 AM
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Default Iím leaning towards fuel

car was running and then started doing this and the guy was frustrated and gave up selling it way to cheap 🙂
I kinda figured I had to pull injectors just didnít really wanna. I know I have fuel to distributor, but after cranking as long as I did the plugs shouldíve been soaked and they were as dry as a bone.

Is it just vaccum that controls that fuel distributor? Possible diaphragm tear ? Again sorry to ask stupid questions, my manual will be here Friday lol
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Old 06-06-2018, 11:21 PM
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Well, the fuel distributor is controlled by air lifting the metering flap and letting more fuel come out of the injectors, but it's also controlled by the ECU, which is supposed to sense how much pressure it needs to send through the system. This fuel system, CIS, was awesome when it was all mechanical, but when they switched over to having parts of it be electronic it became perhaps better when it was new but much harder on us here in the future where components are starting to break down and all the extra bits make it hard to diagnose. I completely understand anyone wanting to get rid of it in frustration.

-Rog
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Old 06-07-2018, 03:16 AM
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Default Got it to run

Decided to pull air boot and saw how injectors got fuel from air box. Lifting the rod and plate the motor would run and stay running due to it forcing fuel from distributor.
I had thought maybe an obstruction wasnít allowing plate to move (mice building a nest etc) but it was free so looks like Iíve found my problem and Iíll be looking for a distributor assembly.
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Old 06-07-2018, 07:57 AM
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Before you swap it out you might check to see if anything was messed with by someone trying to fix things without knowing what they were doing. Suspects would be the idle screw, and the CO idle screw. You may need to wait until you get your manual for those as I don't have any pictures handy and it's more of a process. To me it sounds like the fuel distributor may be working properly, just not in the correct way. You may even have a lingering vacuum leak somewhere. Have you tested it with smoke blown into the vacuum system? That's really the only way to be sure.

Some links that might be useful:

https://audi.humanspeakers.com/tuning-cise.htm
https://audi.humanspeakers.com/timing2.htm (Skip the timing part for now, maybe this will help with the basic settings part.)

-Rog
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Old 10-16-2018, 05:24 PM
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Also check that the ECU has it's fuse in place.. Often gets mistaken for a 'spare' fuse, then gets reused somewhere else..

It should be the only fuse in the 'side' row of fuses, that are closest to the fender. Look down in the fuse openings, and only one of them actually has contacts for a fuse. That's the EUC fuse, and withiout it, may run, but not well. Fuse #20-someting..

As mentioned, is also a good reference.. https://audi.humanspeakers.com/tuning-cise.htm

Last edited by Katman; 10-16-2018 at 05:26 PM.
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Old 11-05-2018, 02:04 PM
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Default Finally got injectors out to test

sorry for the long delay, work with boats and havenít had anytime to devote to the Audi.
So I pulled injectors out (which sucked) and put them into bottles. Seem to have no fuel going to the injectors really. As you can see in the pic that fuel amount was three attempts of pulling on the air plate.
What I donít know, cold start valve had tons of fuel, does it push all fuel to that over injectors? Fuel in pic looks super dirty and it may be clogged/crap in them, but I also blame the fact that the injectors were covered in oil. The gf is a chef she helped as much as possible trying to keep them upright, but...
any help would be super appreciated!!
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