No-start electrical problem, suspect ECU...?

Just bought a 96 passat with the 1z for a song and tryna turn it into the family grocery getter... seemed a fitting replacement for our old 1980 dasher 1.5l IDI which has recently been retired from daily use. Now, i'm quite familiar with that engine and pump but the B4 has me scratching my head with a strange problem that i can't diagnose. I'll enumerate the facts and maybe has an idea? don't have the shop manual yet (ordering one tonight), i'm sure a schematic will help but here goes...

* about 9 times out of 10 the engine will crank with no fire. when it does start it starts immediately. engine runs well and it's never conked out whilst running.
* this did not happen before i made my electrical "fix". the starter would not crank with the ignition in start position and after trying unsuccessfully to find the clutch lockout switch i wired past the interlock, reasoning that this was fine since it started just fine with key on / jumper to the start terminal on the starter.
* when i turn the key to the on position the glow plug light sometimes flashes twice rapidly and then turns off, more often doesn't light at all (though the CEL does light) this is seemingly a flag for the relay 109 malady but i checked it, it's the gray updated one and i removed the cover so i could watch it contact, also tried jumping the terminals with relay out. also, jumping the shutoff solenoid has not made a difference. and i removed the solenoid and it seems to work just fine... i guess i can try what i just read about removing the plunger to make sure, but it seems to be ok.
* while driving the check engine light is on (though this has only been the case since this whole episode started) and periodically the glow plug light will flash while the vehicle is idling, stops if you give it some gas. also it now idles at around 1100 whereas i believe it used to be more like 850.
* when i bought the care the ECU was hooked up and hanging under the dash... in the proper mounting location there was another one, presumably the original. the new one has a large dent in the housing. it was a proxy sale and the guy i talked to couldn't tell me anything about the history or what the p/o might have been thinking. tried plugging in the old ECU and nothing changes... runs the same when i can get it to start, which is once inna blue moon...
* key on, there is often but not always a chattering sound from the IP which lasts about 6 seconds. seems to come from the top of it but i can't really feel the vibrations so hard to say for sure. *** is that?

so my experience with VW diesels ends with that old dasher which would never have these types of issues... with the shutoff blocked open can the computer still keep it from starting? is there something in the starter interlock circuit that serves a function beyond safety? i wanna suspect the computer since there's such a complex web of electrical gremlins but it's a pricey gamble and both ECUs act the same... any help is appreciated, its driving me up the wall... and yeah, i'm buying the shop manual...

When you say that when it starts it starts immediately, do you mean that it doesn't crank a bunch, or that when it catches it catches good?

I'd be nervous about the electrical stuff, but there doesn't sound like any other problems that wouldn't otherwise be described as a problem with air incursion in the fuel. So...

Do the problem starts occur after sitting for a long period of time? Short period of time when warm/hot? Generally there's SOME pattern. (parked uphill, parked downhill etc.)

Does this have a clear line going to the IP? If so, are you seeing any air in that line after the car has sat?

Sounds like it could be a crank position sensor to me. It'll allow it to crank but the engine doesn't know the timing so it prevents fuel from being injected. I wonder if a wire is chafed or crossed. It really needs a scan. If the ECU is the black case, you need a VCDS to scan it, if it's silver, it's OBD-II and most scan tools should work.

Bad wiring to the IP will cause the same thing. Check the wires under the collet shown in the picture, which is just to the left of the injection pump. They're a known chafe point on these engines.



There is no clutch interlock on a B4. That clutch switch is for the cruise control interrupt.

The chattering is probably the stop solenoid being pulled in, which shuts off after the car doesn't start in 5-10 seconds.

Try and get a scan if you can. It'll help a lot.

when it starts it starts within a second of cranking. otherwise not at all for love or money. and it never stumbles or dies once running. and so i think it's in the initial computer power on sequence... and seemingly very random. either it decides to deliver fuel to the pump or not... i will attempt to borrow a scan tool tmrw, it is the silver ecu so mebbe the autozone one will give me at least a number or two... but yeah, the causal chain with the electronically controlled pump is a mystery to me, had thought it was just for tuning and that it would at least provide fuel with the shutoff pinned but not so... also, i guess i'm not familiar with the vehicle and compared to the 1980 dasher it's zippy as hell, but nothing seems to indicate obvious limp mode, it's quite responsive once running. guess i got a lot to learn. abacus, is there a way to test CPS function aside from blind replacement?