Fuel pump prime on D jet FI

[cmscott]

Hello All,

The latest problem Im having sounds very electrical. My car is a 1968 VW Squareback with the D-jet still installed. The problem is that I have an intermittent start or stall issue. When I turn the key to the ACC position and the fuel pump primes the lines, it doesnt always prime for the same duration. I can feel the relay under the dash and under the rear seat click when I turn the key to the ACC position. IF the fuel pump prime duration is like its supposed to be, 2-3 seconds, the car starts just fine and all the injectors show to be firing according to the noid light. IF the prime is only about a half second, the car wont start. It seems like whatever tells the fuel pump to prime for 2-3 seconds isnt responding very well. Its kind of hit and miss. Sometimes the car will run and sound perfect then just suddenly dies. Ive stuck a noid light in the back of the injector and no fire shows although the trigger points bounce the ohmeter back and forth all day long (check good). Every time the car dies, the fuel pump prime duration is very short when I move the key back and forth in the ignition switch. And every time the car dies the injectors arent getting the SIGNAL to fire. Any ideas? I tried to go to the parts store and buy a FI relay with the bosch cross reference and, of course, they sold me the wrong one. The old one is back in there now. Any help or ideas on what to check next would greatly be appreciated. BTW, I have a FI wire harness on order. Even if its not the harness, I was planning on getting one anyway.

[Tram]

Check fuel pressure when this happens. My best guess is the pump is getting sketchy.
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[cmscott]

So if the pump pumps below the 28 psi that the injectors need, would the injectors sense that and not open below that pressure? I ask because when this happens and I try to restart it, none of the injectors are even getting signal. I check this with a noid light. Would the ECU somehow tell the trigger points to stop sending the "fire" signal to the injectors if fuel psi was below the needed pressure? Im just not sure how smart the ECU really is, thats why I ask. I dont have a fuel pressure guage right now, Ill have to borrow one tomorrow. And by the way, the fuel pump doesnt seem to be getting hot, only warm. I have recently, in the past six months, cleaned the fuel pump (diesel backward thru it method) and had the tank professionaly cleaned and sealed. Thanks again.

Chris Scott

[Tram]

[KTPhil]

[cmscott]

I checked that ground, and every other ground I could find in and around the fuel injection system. Ive filed the injector and FI relay (the one under the seat) grounds. Replaced battery cables and ground strap from the transmission to frame, and filed all those, too. All sensors have been checked and proven good. I was just out there and the fuel pump buzzed to life for the 2-3 seconds like it is supposed to and the car fired right up. What about a sticking relay? How would I check that? Like I stated, the FP and FI relays both "click" when the key goes into ACC position. There is one wire that Im not sure where it goes, but its brown, so Im guessing its a ground. It is located just in front (front of car) of the driver side intake runners. It sticks out of the wire harness (it is connected though) that runs behind those runners. Is this a FI related ground? Lastly, is the ECU grounded anywhere? If so, where? I could check that ground, too. Thanks again.

Chris

[Bobnotch]

[KTPhil]

The ECU isn't "smart" at all. Oh, the naivety of the digital generation!

This is not a "computer" as you understand them today-- operating system, digital inputs, programmable decision-making, and outputs. It's an analog circuit that modifies pulse width, nothing more.

No "limp home mode", no default values, no error-checking. Oh, and no software whatsover!

Think of it more like plumbing, with a couple of flow-restrictions operated by thermostats, and one operated by air pressure.

Which is exactly what it is!

[vlad01]

Can't remember the exact number, but there is something like 12 transistors in these ecus. No ICs, no ram, no bus systems, nothing. Modern processors have over billions of transistors now, although an ecu would have more like 10s to 100s millions of transistors. Yes that's right the type 3 ecu is merely an analogue /digital hardwired circuit.

[cmscott]

Can trigger points go out intermittently? Is there anything that could cause them to "miss"? Every time I check them for ohms, volts, and continuity, they seem fine. I ask because every time the car doesnt start or dies, it still has spark, but ALL the injectors wont fire according to a noid light.

Fuel pressure is good when this happens and pump is not hot. When the car dies, it sounds like the key was turned off. No dieseling, no sputtering, no smoke, no gassy smell, and no hunting idle. It just dies like all the injectors stop firing at once.

I read another post from another member about his car having very similar symptoms. I messaged him and he said he ended up just buying a new ECU for it and it was fine after that. I know if the car starts at all, its not the brain, but could it be dying and intermittently going out? I ask because every time the car dies or doenst start, everything else checks out good. Thanks.

Chris Scott

[Mike Fisher]

You can pull your distributor and clean your trigger points with a dollar bill. They do accumulate crud between the spring loaded contacts.

The ECU can go bad. Your '68 should have an A or B ECU.
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[KTPhil]

Intermittents a more likely to be the connectors or wiring at the trigger points circuit, rather than the points themselves, or the ECU.

[cmscott]

Ok, thanks for the replies. I do have a B ECU. And I have cleaned the trigger points. For troubleshooting purposes, what would be a good "parts store" relay to buy to replace the FI or fuel pump relays? Ive heard the rear defroster relay is ok to use or any quality fog lamp relay. I know it has to be "normally open", right? If someone has a "parts store" part number that would help. I was hoping the car wouldn't start this morning so I could troubleshoot it, but of course it fired right up every time I tried it! Figures...

Also, does the D-jet system need a solid 12V to run properly or is there a range it can use? I ask because when all electrical accessories are on, voltage seems to drop to around 11.7-11.8V to important stuff, like the fuel pump. When all electrical is off, fuel pump is getting about 13.4V. Thanks again.

Chris

[KTPhil]

Apparently it runs richer when the voltage drops. That means with a generator, which doesn't charge at idle, voltage will drop to or below battery voltage. Ergo, it may run wich when idling. I have never seen this quantitied, though (like percentage enrichment for a given voltage drop).

[vlad01]

Most likely trigger points or associated connection. But it certainly can be be the ecu, dry solder joints, broken component leads or faulty component quite often do cause intermittent problems. Run the engine an give several good thumps to the ecu and see if it kills the engine. If it does the problem is in the ecu. Also check ecu power supply wiring and connection too.

[cmscott]

So I have a pair of trigger points on order. More for trouble shooting than thinking this is the problem. Back to the first response I recieved from my original post, I crawled up under the car and the pump seems to be getting a little warmer than "warm", but I wouldnt call it "hot". Replaced the three month old filter and the tank has been professionally cleaned and sealed in the past six months. I actually turned the key into the ACC postition and it took about 5 or 8 seconds for the fuel pump relay to click to prime. Could it be a sticking relay? I did the pump-in-diesel thing already to clean it. I wiggle the ignition switch and it doesnt make any difference, so I dont think thats it. Fuel pressure at engine is good, but havent checked it coming out of pump. What should the pressure out of the pump be? What should the volume of the pump be? The "buzzing" of the pump does seem to be a little louder than I remember, but I could just be wanting to hear that so I can blame something already. How can I determine if its a $190 pump or a $20 relay? Thanks again.

Chris Scott


I did check the ECU connections and gave the ECU a good couple thuds and it didnt make any difference.

[JSMskater]

[cmscott]

How would a short-to-ground affect the FI system if the short was to a different component? Im pretty sure I had a short-to-ground because I disconnected the battery negative and I saw some very small sparks. Not big crackles like when the wrench slips! I put a relay in front of my amp for my radio and it seemed to go away, along with the electrical issue. I know amps pull a lot of amperage, so could it have been pulling too much power from the FI system and killing it? I dont have a big "system", just four speakers, an amp, and an mp3 hookup. I drove it around my "proving grounds" (a close radius to my house in case my wife has to bust out the tow straps!) and it didnt even hiccup. And yes, I know I shouldve put a relay in the first place. So could a short-to-ground mess with the entire electrical system? Hopefully it gets me to work tomorrow....Thanks again guys.

Chris

[Bobnotch]

[cmscott]

I do have an alternator. And I didnt even think about the dome light being on. I could turn it off and disconnect the battery again to see what happens, but I think it was on and I didnt see any sparks. I drove the car today to work and back (27 mile round trip) and it didnt leave me walking, so Im thinking it was the larger amperage draw of the amplifier messing with the system. Ill call it "case closed" until the next problem.....

Thanks again guys,

Chris