Hey guys.
customer recently brought in a 91 GTI. We thought it was a fuel leak at first but realized quickly that the gas was leaking out of the exhaust flange from INSIDE the exhaust. We pulled the plugs and found A LOT of fuel inside the cylinders. The car has spark but is for some reason jetting WAY too much fuel into the combustion chambers. Any help would be appreciated.
Thanks Jesse
16V or 8V engine?
I'm not familiar with the 16V engine but if this is a USA or Canadian 8V model it should have Digifant injection. If so, then check two things...the vacuum line that controls the fuel pressure regulator at the end of the fuel rail on the passenger side of the car (it looks like a little brass colored metal can/valve on the end of the fuel rail behind cylinder #1 on the back side of the valve cover). Make sure that vacuum line to it is OK. It's easy/cheap to replace too with typical rubber vacuum hose (the OE hose is cloth covered but I don't think that matters). if it looks bad, just replace it. Careful pulling it off because if the engine is hot *and* if the fuel pressure regulator is bad/leaking internally, you might get some fuel spillage. So make sure the engine and exhaust manifold is cool when you do this. if you do get spillage when you remove the vacuum line, then the fuel pressure regulator is bad. Replace it (it just unbolts and you just bolt the new one in place and make sure to get a new o-ring too).
If necessary either before or after, you can depressurize the fuel system and get some of that excess fuel out of there by starting the car and pulling the fuel pump fuse. It should idle for a bit and then stall out.
The 16V engine I think is CIS-E Motronic. I'm not too familiar w/that engine but I think (someone correct me if i'm wrong) the fuel is metered by a fuel distributor and individual fuel lines being sent to the injectors. The fuel distributor or something controlling it might be faulty but I don't know any more detail than that.
And the vacuum lines themselves are ok too (none leaking)?
I suppose that's possible but I don't know how to troubleshoot that one.
Check for short-circuits to chassis in the injector harness.
The ECU pulls one injector pin down to chassis (ground) in order to open it. The other pin on each injector should be at battery voltage.
You can remove the injector harness plug and crank the engine with spark plugs removed. That should identify any leaky injector without removing it.
Check the ground wires to either the intake manifold or to the coolant pipe on the cylinder head, the pipe over the trans. Sometimes these wires break causing the engine to run rich. Also check switches and wiring at/to the Throttle Body.
Coolant Temperature Sensor could also cause a rich running engine along with faulty 02 sensor wiring. Fuel Pump Regulator is a common problem and may not always consistently leak! 8^o
there's rich, and then there's outright flooding. this one sounds like it's flooding from how they described the fuel situation after removing the spark plugs.
CTS and O2 sensors can cause rich running, yes, but never heard of them causing flooding like this.
fuel pressure regulator could still be it (even if not leaking), yes, or something w/the fuel injectors (and/or what controls them). My money is that it's something in that area of the engine and not the inputs to the ECU from (a bad) CTS or O2 sensor. Just a gut feeling though, that's all.
SOOOO many could be-s and even multiple problems. might be a partial ign. problem where the spark is not strong enough to fire extra fuel being dumped inside of the engine.
I would need to see it and test components. AND you might as well test everything to start ruling out possible problems. ;-)
later, dave (One out of many daves)
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