CIS Problem?--AGAIN!!!

John Cody Forbes cody at
Mon Jun 26 13:20:29 EDT 2006

L DC wrote:
> Sorry, I did not get a response so I'm reposting this.
> Many Thanks again Cody!!
> Could you please clarify a few things?
> Cody Wrote:
> < You are correct on leaking fuel into the combustion
>> chamber, which is why I don't think you have bad
>> injectors.
> So, if the car had leaky fuel injectors, the car would
> still start, but it would run crappy, right?
> I mean, fuel + air + spark in the combustion chamber
> will make the car start, albeit crappy perhaps and
> might shut off if the combination is not right.

If the injectors were leaking it would be hard or even impossible to start 
due to flooding. Once running the leaking injectors are spraying full time 
so the problem is insignificant. The big problem occurs when you shut the 
engine off and the leaking injectors drain the pressure into the ports and 
chambers through any open valves.

>> Other possible pressure leak-downs occur at the
> check > valve on the fuel pump....
> So far I'm ruling this one out given the fuel pump,
> Pierburg, came with a brand new check valve.
>> ...and the pressure accumulator in front of the right
> rear wheel under the car.
> This could be a possibility as I would bet this car,
> as most its era, has the original pressure accumulator
> This a pic of the accumulator from your web site,
> right Cody?
> Do you know if a part from an Audi non T, not Q from
> either a 5K or 100 is interchangeable with that of the
> 5KTQ?

Yeah thats the rusted nasty accumulator on my black 5ktq when I bought it, 
it was replaced with a brand new one later that day ;-). It didn't fix the 
problem I was having though. I'm going to bet they are the same for almost 
all CIS cars, even 911 accumulators look identical.

> In what other places could there be a pressure
> leak-down, aside from the obvious fuel lines running
> under the car or engine bay?
> But even with a pressure leak-down, isn't there still
> enough pressure being built by the fuel pump to at
> least make the car start?

As for other places to leak down pressure, I think it's limited to the 
warmup regulator, FP check valve, accumulator, injectors, and leaky fuel 
lines. There is not enough pressure being built under normal circumstances 
because CIS runs at very high pressure (60psi sometimes as high as 100psi), 
and the pump only runs when the engine is being cranked. With all the volume 
in the lines, fuel distributor, accumulator, etc. it takes a while to build 
pressure. That said, I don't think the problem with your car is related to 
pressure leakdown. Because your car still wont start even with the fuel pump 
running constantly (fuse in relay) I think your pressure is fine, and the 
problem is somewhere else. See if you can get it started, then let it warm 
up and shut it off when hot, then immediately try to re-start. If it does 
start when hot then I'm going to point my finger at the warmup regulator 
mounted to the block on the drivers side.

> It almost seems to me that the car is simply not
> getting fuel delivered to the combustion chamber.
> Maybe I'll disconnect the fuel line leading to the
> fuel filter and if I get fuel there and I will pull
> one of the fuel injectors to see if spraying.

Pulling an injector is a PITA unless you've done it before and have a feel 
for it FYI. They like being stuck very firmly to the head. It is a good way 
to see whats going on though.

> So which do you recommend Cody, option 2 or 3?
>> Option 2:
>> Factory wiring. You can use the much safer method of
>> using the factory wiring so the pump automatically
>> turns off if the engine stops (ie. in event of an
>> accident). This is the most simple method, but it
>> does leave the OEM fuel pump fuse and relay in the
>> way in case they go bad. For this method follow the
>> diagram I made exactly.
>> EOM fuel pump.... meaning if anything goes bad in
> that wiring, the pump won't run, right?
> Also, by taking this route I assume I will be using
> the "green and yellow" wire that comes from the OEM
> fuel p relay and not from any nearby hot wire,
> correct?

Correct, if the factory wiring, fuse, or relay go bad it would shut off your 
pump. Also correct on the green and yellow wire.

>> Option 3:
>> Direct to ECU. You can run a whole new wire all the
>> way to the ECU.
>> It's alot more work, but I recomend the second
>> choice.With this choice it's actually slightly
>> different then the wire diagram I made. The ECU
>> turns the GROUND on and off, not the positive, so
>> you have to run the wire from the ECU to the new
>> relay (where I labeled "from green and yellow wire),
>> then the other wire from the coil of the relay
>> (where I labeled "Chassis Ground")goes to the
>> battery positive. The other two go exactly how I did
>> the diagram.
>> The pin on the ECU connector is pin #21
> For this method, I assume the relay labeled "From
> Battery + " would then go to a chissis ground, right?

No, from battery + would still be exactly that. You would have 2 battery + 
wires to the relay, then one going to the pump and one going to the ECU. To 
do that you can just run one battery+ wire, then when you crimp on the spade 
for one connection also crimp in a 3 inch section of wire with another spade 
on it so you can connect to both parts of the relay.

> Would the wire running from the new relay to pin 21 on
> the ECU hook up easily or would it require soldering?

Well you could crimp it with a butt connector, or you could solder it. I 
won't say which I think is better because theres a big debate on this list 
between the two that I don't want to start up again. You would cut the wire 
comming from pin21 a few inches (5 or so) from the connector then connect it 
to your new wire with your method of choice.

> Just curious, what happens to the other wires that the
> fuel pump hook up to?
> One is a ground, the other would hook up to the wire
> (hot) running from the new relay, what about the other
> 2? I know 1 of those other 2 wires is a hot wire also,
> can't recall on the other.

There are only 2 wires to the fuel pump. The other 2 on the connector on the 
tank top are for the fuel gauge.

-Cody Forbes
'86 5k noT noQ
'86 5k noT noQ - Parting Out
'87 5ktq
'87 5ktq - Fast. Really Fast. 

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