Fuel Injectors not firing, bad ECU??

[apocacist]

I'm sure this type of thing has been covered ad nauseum here, and believe me I've spent countless hours reading through things and searching. There is one thing that I cannot find: how do you test if the ECU is bad?

I have gone through every test in the L-Jet manual. Everything looks good, the FI wiring harness is good, etc etc. Here's what I'm seeing:

I pull the injectors out, place them in containers, turn the key and nothing sprays. If I bridge the terminals in the ECU harness to the injectors, and turn the key, they spray great.

Now, if the ground pulse from the "-" terminal of the coil isn't getting fed into the ECU, then that could explain this. However, my multimeter just isn't fast enough to measure that quick of a drop. I have a 3.5V-120V test light that does indeed flicker... but I can't tell if the 12V signal is dropping to 0V as it should or just dropping to a lower value.

The other problem I'm seeing is that I get a nice bright blue spark off the main coil wire but only a bright yellow spark off of the spark plug wires. (new cap, rotors, wires, electronic ignition instead of points/condensor). Is it possible that the coil (also new) somehow isn't getting fully discharged and therefore the signal going into the ECU isn't dropping all the way to 0V?

And here's one more thing, which is ultimately making me hesitate to buy a new ECU: the bus was running great but would horribly misfire and buck at high speeds once warmed up (I have a new and tested T2 sensor) and also couldn't hold an idle when warmed up. When it died, I was driving it much longer than I should have been (about 45 mins) and it was bucking terribly. It hasn't started since.

Any help would be greatly appreciated!!

[raygreenwood]

You cannot fire the injectors just by turning the key on. You "might" get them to fire once ...as you note with a dumped coil...but as you surmise you will not be fast enough.

Putting things really crudely....First....the ECU needs to see air movement with flow through the meter to turn on the pump. The ECU sees the firing cycle of the coil....creates a square wave to run the injectors...injectors open...coil cycles...wave collapses...injectors close (might be vice versa)..cycle starts over.

First...pull your injectors out of the ports and lay them on rags. Hot wire your pump direct to battery and check you fuel pressure both with no vacuum at the FPR and with vacuum using a hand vacuum pump. Turn the pump off and time how long it takes to bleed down. If you correct pressure and are not losing pressure too fast after shut down and your injectors are not leaking from the tips....the pump, the regulator and injectors are at least sound for fuel flow.

Check the resistance of your injectors. If they match the book....and can be clicked open with a 9V battery...and in those 2-3 seconds they have a good spray pattern....they are good and no further testing is needed unless you send them out for cleaning.

I suspect you have a loose ground...and this can include the ground strap at the battery or transmission...or even a poor ground at the fuel pump or main system power relay.
Or a bad spot on the carbon trace in the AFM....this will cause bucking at certain throttle positions....but this usually will not cause lack of start.

Other common items that can cause bucking and "may" digress to a very hard start condition is a torn or frayed copper ground braid on the distributor breaker plates.

This bucking can also be caused by bad connections at the female connectors inside the harness...when they crack or fray in the strain relief area. They can easily escape detection with a volt meter because their connection issue is caused by vibration while running.

The bucking and then no start...is also a common feature of a plugged up sock filter in the fuel tank. Ray

[apocacist]

Thanks for the input, Ray. I'm 99% sure that the fuel delivery system is okay. If I bridge terminals 36 and 39 in the AFM connector (to turn on the pump) and then bridge the injector terminals in the ECU connector, they spray great. And I've somewhat verified fuel pump and pressure by connecting a hose to the fuel line, turning they key and aiming the hose away from me... it sprayed like 15 feet.

A test light flickers on the injectors, but again, i cannot tell if they are actually going all the way to ground or not. As best as I can tell, the signal only drops to about .5V (again, REALLY hard to tell with my multimeter) which I don't think is enough to fire the injectors.

(edit) I have a new FI wiring harness. When I tested my 40 year old one, I found leaking current all over the place... pins connected with 40ish ohm resistances when they shouldn't be. So, I'm glad I got the new harness, even if it wasn't the ultimate culprit. (end edit)

I've been strongly suspecting something with the distributor. It has a single vacuum advance and when I hook up a hose and suck as hard as I can, it only moves a degree or so. I don't think this would prevent starting though.

Is there any way to measure the pulse coming off the distributor/coil accurately without using a professional oscilliscope?

[Tcash]

, electronic ignition instead of points/condensor)
Which electronic ign. Pertronix will not work with fuel injection. Unless they came out with something new.

Put the points back in.

Determine if it is fuel or spark.
Cranks Won't Start Test

Make sure the coil is a resister coil.
http://www.ratwell.com/technical/BlueCoil.html

Ignition High Tension Leaks

Good luck
Tcash

[apocacist]

I have a brand new, within spec, bosch blue coil.

I'm using "hot spark" https://www.hot-spark.com/1-air-cooled-vw.htm

It is sparking... again, not sure why i'm not getting a bright blue spark. I do have a new set of points/condenser as a backup... But to be honest, and perhaps a little bit embarrassed, I'm not exactly confident I'm setting the gap correctly. If the points are opening and closing, is that at least good enough to get a rough start/idle?

I'll step out to my shop in a bit and take a hard/close look at my distributor.

[SGKent]

many electronic ignitions won't work right with FI. L-jet relies on the pulse from the points going into the coil primary to tell it that it is time to open the injectors. Why some people have no trouble with electronic ignitions and others do I can't fully tell you. See the Probst book for an explanation how L-jet works. Make sure the trigger wire to the ECU is connected to the correct terminal on the coil. You can pour a table spoon of gas into the plenum etc and see if the bus will run on that for a few seconds. If so then for sure you have a fuel problem.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[Tcash]

Tune up

How to replace or adjust the points and condenser on your VW
https://m.youtube.com/watch?v=MoQbmuMploc

[aeromech]

Why people choose to replace points with the distributor installed is beyond me. Just so much easier to do off the engine. You’re supposed to reset the timing after changing points anyhow. So much easier to clean and lube. The find high lobe and set the .016 gap. Place a dab of distributor grease on the cam and spin it around. Recheck the gap and install back into the engine. It’s not possible to index it wrong like some other engines.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[mikewire]

I had a similar issue after putting my FI engine into my 1972 Deluxe. The problem ended up being one terminal wire that appeared it need to be grounded, but did not apply to my application (located near the high altitude switch) and needed to be disconnected.

So maybe double check that out!

My thread is here if you'd like to follow my troubleshooting steps: https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=40
_________________
-Mike

@countdowngarage
@bigskyeuro

1972 VW Kombi 9 Passenger Deluxe w/ 2.0L F.I. VWAC swap
1965 VW Beetle Deluxe Bahama Blue

[furgo]

I can only offer an answer to one of your questions myself. Hopefully what others have said can steer you in the right direction.

[apocacist]

Gents, I haven't looked at my distributor yet. I took my well needed 7th day of rest today

I've seen some conflicting things about how the coil operates. Here's my understanding, and I would be grateful if anyone with expertise could confirm or correct me:

The coil has a "+", "-", and center (high voltage) terminal. 12V is applied to the "+" which very quickly brings the "-" up to 12V. At that point, the coil is energized. When the coil is discharged through the distributor, that causes the "-" terminal to drop to 0V or ground. It then is quickly brought back up to 12V as the coil is re-energized and the cycle continues. Therefore, the "-" terminal ought to have a 12V to ground square wave type of signal coming off of it. This connects to ECU pin #1 through the wiring harness. The ECU uses this signal to time the injector pulses and the length of each injector pulse is determined by a myriad of other signals input into the ECU from the various other senors attached.

Based on the behavior before it died, I really strongly suspect it's related to the distributor signal and not the ECU, despite all the L-Jet tests telling me to replace the ECU. I don't know exactly what the ECU does with the ground pulse from the distributor/coil, but if it redirects that pulse to the injectors to make them fire, then if that pulse isn't going all the way to ground, neither would the injectors.

I'll get out there and do my points/condenser in the morning, check the braided copper wire inside the distributor, and check the one ground that I haven't yet checked (the one for the transmission?). Unfortunately though, without a good way to test the coil/distributor pulse, I will have no way of knowing if I even did my points correctly . Well, unless it starts after that.

[Tcash]

[furgo]

[raygreenwood]

[furgo]

(double post, sorry)
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[Tcash]

[apocacist]

Thanks everyone for all the info. And especially those graphs showing the coil and injector pulses. Those are awesome and exactly what I was looking for. It really helps me to understand how the L-Jet system works.

Well, I took out my distributor and completely broke it down, cleaned and lubed every part, and put it all back together with new points and condenser. The copper braided wire connecting the breaker plates looked good and was well soldered onto both plates.

I don't have a dwell meter, but I am getting sparks. I was unable to locate any ground underneath the bus near and on the transmission though. However, I have checked the 3 sensor grounds underneath the #3 intake manifold, the system ground off of the double relay, and the battery ground. If I'm not mistaken, this takes care of all the grounds used by the FI system.

Still nothing. The engine is turning over from the starter but it doesn't sound like any ignition is taking place. I'm going to go through all the checks in the L-Jet manual one more time before I replace the ECU.

P.S. I removed the ECU, took the cover off of it, and visually inspected the components. I'm not seeing anything obvious. However, there is one transistor on the side that appears to be connected to all four injector pins that cannot be simply visually inspected. It looks like this: https://radio-antigua.com/images/10814%2027.JPG

I am unsure at this point if I feel like it will be worth trying to replace that one component. It's worth noting, however, that the ECU from BusDepot.com has a core deposit which means they intend to fix them... I'd really like to know how they do that!

I will post again after running all the L-Jet tests. Thanks everyone!

[apocacist]

I found a mechanic that specializes in old VWs nearby in Longview, TX. I kind of thought I was all alone out here in East Texas! I will probably give them a call and see if I can bring them my ECU to have them test it.

[aeromech]

These ECU’s are pretty tough. Before dong anything else open up the ecu and take a close look at the circuit board. Look for burned areas/broken solder joints. Do the sniff test. Usually you can the fault.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound