VWDiesel.net The IDI, TDI, and mTDI source.
General Information => Troubleshooting => Topic started by: rabbit_diesel on June 16, 2009, 12:39:28 pm
-
I just finished swapping the automatic tranny to a 5 speed on my '92 Mk2 Jetta. When I tried to start it, it seemed like it had too much compression. So I took the spark plugs out and I turned it over again with the starter and gas just sprayed out of the spark plug wholes. I don't think that's supposed to happen. I know this is a diesel website, but please try to help out. I would like to know why it is doing this. I wish I could just put a diesel in it already.
-
Digifant FI will push tons of fuel when cold, even when there is no problem. But the most likely problem is the ground wires that normally are attached to the coolant flange on the side of the head. Even if they look ok , cut them and use a good connector and attach them to the side of the intake manifold, or any other good spot on the motor. Also make sure the temp sensor is working properly.
-
THIS SAME CRAP HAPPENED TO ME!!!!!! RIP THAT ENGINE OUT AND DROP IN A DIESEL :o
no seriously... the car ran, and then dumped fuel into the cylinders to the point the starter couldn't even turn it over. wait about 10-20 hours and it all drains to the sump, dilluting the oil to the consistency of near diesel. its absolute garbage. i absolutely LOATHE these engines.
-
Typically this means the injectors are being left open... usually because the ECU is erroniously telling them to do so.
Some troubleshooting thoughts:
There's no computer to check for codes... gonna have to troubleshoot this old skool, starting with the ECU grounds on the valve cover, as Caveman suggests.
Next would be to get a multimeter on the injector electrical line (all 4 injectors come on at the same time) and see if in fact they have voltage full time. If so, you suspect the ECU... yanking it should make the voltage go away.
The quickest way to test the ECU itself is to swap out one from the junkyard... the Bentley has a series of tests you can perform but they really only confirm that the ECU is getting the right signal... and no set of signals should cause the ECU to leave the injectors on full-time.
-
I was looking at all of the grounds and I noticed there is a ground cable that runs from the valve cover back to the coil mount. That must have broke in half during the tranny swap. I reconnected it and tried it again with no luck. How could that one little ground wire cause the whole ECU to be shot?
-
I was looking at all of the grounds and I noticed there is a ground cable that runs from the valve cover back to the coil mount. That must have broke in half during the tranny swap. I reconnected it and tried it again with no luck. How could that one little ground wire cause the whole ECU to be shot?
Well, I'd be inclined to hunt down a test ECU before calling the ECU a gonner... but in general if you feed power to a sensitive electronic circuit without a proper ground current will flow thru paths the manufacturer never intended, with unexpected consequences.
There should be a thick copper braid (which I believe just grounds the coil) *and* at least one thin brown wire with a white strip, usually two brown/white wires in fact. Are they all there and connected to the valve cover ?
-
Yes, I believe those wires are safely connected to the valve cover along with the braded ground wire that goes to the coil (the one I had to fix). Did I mention that it doesn't have spark?
-
Nope, that's new.
Sounds more and more then like an ECU that's gone to meet its maker... if you can find one to swap it's the quickest way to eliminate/confirm as a suspect.
-
just to let you know what fixed it was another ECU. car was sold shortly after that...
-
There is 2 grounding issues with those models- if the motor was cranked without all the grounds connected, it's a sure fire way of toasting the ECU. Also if the spark plugs are not tight it can cause ECU grounding problems.
-
doesn't surprise me with the ground issues... those cars were rust buckets if not properly maintained.
-
if the motor was cranked without all the grounds connected, it's a sure fire way of toasting the ECU.
That's exactly what could've happened cause the tranny I put into it was painted and I was kind of in a hurry to get her back together and... well, right when I went to start it all lights on the cluster went out :-X and it was making weird clicking noises. I'm just glad that I have a good theory that this is what the problem is. I ordered an ecu box online for 40 bucks shipped. So, all should go well... hopefully ::)
-
My sister had a 92 Jetta 1.8 for a few years,
and one day it would not start for her.
When I got there, there was no spark at all,
and it ended up being the "Ignition module"
(small computer thing on top of the ECU on the metal cover).
The only reason I got it fixed quickly is I had brought an ECU, Ignition module, Coil, and distributor
from a donor car.
I think her hall sender was also troubled,
but that was years ago....
-Brad
-
there was no spark at all,
and it ended up being the "Ignition module"
(small computer thing on top of the ECU on the metal cover).
-Brad
Well mine doesn't have spark and plus the injectors are malfunctioning. Could I also need one of those little ignition module boxes? I sure hope not :'(
-
there was no spark at all,
and it ended up being the "Ignition module"
(small computer thing on top of the ECU on the metal cover).
-Brad
Well mine doesn't have spark and plus the injectors are malfunctioning. Could I also need one of those little ignition module boxes? I sure hope not :'(
this is why you need to go diesel ;D
but seriously, you might just want to find the mechanical fuel injected engine, and swap that in. those things are near bullet proof and don't fail like the one you have now. plus during the nuclear war, your car will still run ;)
-
Well, if you have no spark, I wouldn't automatically assume that you have a bad ECU.
You need to start from the bottom and work up.
Your car runs DIGIFart fuel injection. Fuel is metered by the ECU. On the old CIS systems, fuel flow was continuous and mechanical. On DIGIFart, fuel flow is metered by electronic injectors (true EFI), and pressure is regulated by a diaphragm on the fule rail. Fuel pressure is not as important on the DIGIFart as it was on the CIS, and the injector valves open under electronic control, rather than increasing fuel pressure. The amount of time the injectors are open, is a function of the air flow (measured by the MAF), engine temp (measured by the sensor), and the amount of oxygen in the exhaust gasses (O2 sensor).
Operationally, it's a pretty simple system. However, the ECU's and MAFs can easily screw up operation. The ECU was the most common failure point as noted by others, due to the problem with ground wires. Once the wires broke or lost contact, the ECU essentially was fried.
The ignition however, was a completely separate entity. Not until the MK3 (with a crank position sensor) was ignition timing completely controlled electronically. Up to 1992, the distributor worked just like a normal vacuum advance dist found on most cars. On the CIS, the advance was controlled by vacuum, with spark distribution controlled by the Hall sender and the ignition control module. The Hall Sender (integrated into the base of the dist., and where the plug comes in), essentially works like the 4 raised ridges would on a points and condenser type distributor. The 4 "windows" on the rotating "cam sensor" tell the coil when to fire. The signal is sent to the ignition control module (usually mounted to the ECU, or nearby under the rain tray), which sends the signal to the coil, which sends an amplified spark signal to the plug.
On later models, an ignition "Knock" box and knock sensor were added. Essentially, these controlled the advance, rather than the old vacuum canisters. Even with this advancement, the ignition was independent of fuel control, which was handled by the ECU, and there still was a vacuum element to the advance (remember the old knock boxes with a vacuum hose attached?). ON the DIGIFart, the vacuum element was tossed, and advance was controlled electronically.
Thus, if you are not getting spark, it means you have a problem in one of those arenas: the distributor, the coil, the ignition control module, or the knock box.
The knock boxes rarely go bad, so you can probably rule that out.
Hall senders do go bad. Especially on the Digifant
The ignition control modules rarely go bad.
The Coils rarely go bad.
What you first must do is the following (all of this is outlined in the Bentley manual)
1) Check your grounds. The ignition system usually has its own harness with its own ground wire. Without ground, it won't fire. ALso, check ALL OF YOUR GROUNDS, including the main one which connects the battery to the body, and then to the transmission.
2) Check that you have power to the coil 2. This usually involves checking for voltage at the #1 and #15 terminals on the sides of the coil. If you do, it generally means the ignition control unit is fine, as is the Hall Sender.
3) Check coil resistivity
4) Make sure you have the correct plug into the Hall Distributor (the plug on the side of the dist), and that it's fully engaged (I had that problem once).
5) Check the other components (cap, rotor, plugs, wires, etc).
If you have spark, but it's weak, then you have a bad coil. If you have no spark whatsoever, I'd start with the distributor, specifically, the Hall Sender.
Once you have spark, then look at the fuel system. I wouldn't automatically assume the ECU is bad just yet. Chances are good, but you need to sort out the spark issue and then move forward.
-
this is why you need to go diesel ;D
but seriously, you might just want to find the mechanical fuel injected engine, and swap that in. those things are near bullet proof and don't fail like the one you have now. plus during the nuclear war, your car will still run ;)
No more worries about it... this car is now a diesel. It was pretty much an overnight swap. I had to drain the gas out of the tank and replace it with diesel, lol. It even had a 5 speed that went in with it. I rebuilt the injector pump. Gas stinks. I love this diesel wow :D.