injector signal from ECU

kh · Post by kh » Tue Feb 22, 2005 4:47 pm

I have a 73 coupe d-jet that I am trying to get back on the road.

Does anyone have an idea why the signals to my injectors from the
ECU are really low?

At 1st, I thought there was no signal at all, but they are there but too
low to get my injectors to fire.

Injectors work fine when hooked to 12V.

Hooked up my 1218 tester and all is well but nothing from the injectors.
They should be clicking away on test-3.

Trigger points check out and I checked injector ground at back of engine and at ECU plug.

Paul Anders great info on the ECU leads me to suspect the ECU output drivers http://members.rennlist.com/pbanders/ecu.htm
but dont know what could have happened since this car used to run.

THANKS!

vwbill · Post by **vwbill** » Tue Feb 22, 2005 5:12 pm

Maybe Ray can help with this one! I know the ground fi ground term under the intake tubes should be chkd and the fi points in the dist. Can you hear them firing when you open the throttle with the key on? I think they should fire like twenty times? Could it be the throttle pos switch being dirty or bad wind? Maybe you have a bad connection at the ecu? Im sure if you've been to the 914 site you have chk lots; that is a great info!
I didnt know the injectors were 12volt? I thought they were less then that? Sorry Im not any help. Did you check to make sure the dist fi cam isnt worn or the shaft moving around? not much help,,sorry bill

albert · Post by **albert** » Tue Feb 22, 2005 6:49 pm

allo, your injector can play from 2 to 12 volts in relation with your air flow distributor ,, and make sure ,all the ground wire have new therminal connector on the ground block ,,,

raygreenwood · Post by **raygreenwood** » Wed Feb 23, 2005 4:04 pm

Weak drivers of course are possible...but unlikely ...as these things are robust as hell! But...are you getting the same level of reading on all four? If so, it my be either low power to the injection system, poor grounds...or most likely ...tarnished connectios at the ECU. Ray

Guest · Post by **Guest** » Wed Feb 23, 2005 5:28 pm

Dang it does sound like a ground problem doesnt it?

I addressed all ground connections that I know about including

the ground point for all the injectors on back of engine.

Power to the ECU looked great and my ecu and connector look
pristine.

All 4 injectors are inactive, and showing the same low signal.
If I pull an injector connector, the tester detects it fine.

The ecu seems to control the pump fine. The tester can control the pump
and if I hook the trigger points connector to my spare distributor
and give it a turn, the pump cycles and the injector signal is observed.

MGVWfan · Post by **MGVWfan** » Wed Feb 23, 2005 5:39 pm

Wow, an electrical problem...or maybe not!

According to info on Paul Anders' site, you should not see 12V steady-state DC across the injectors. They're low resistance devices (2.7 Ohm resistance), and the ECU has a 6 Ohm ballast resistor in series with the injectors. When you add up all the DC losses in the ECU (driver transistors and ballast resistors), the injector drive signal ends up being something like 4-5V. If you lookat the injector voltage with an oscilloscope, you'll see about 12.5V at the beginning of the injection pulse, followed by a rapid decay (fractions of a millisecond) to the steady-state (DC) value of just shy of 5V.

Now, here's a possibility. When I tested my injectors at 3-5V, I noticed only one clicked. The other three were stuck shut by varnish and gum.

I had to force some carb cleaner through the injectors while energized with 4V from a variable voltage supply, then after soaking and turning the voltage on and off for 15-20 minutes, with 20 psi of air pressure on the inlet, they all finally unstuck and started clicking. If your '73's been off the road for a while, I'd suspect varnish and gum sticking the injectors. They're really stout, those D-Jet injectors, and the ECU appears to be pretty stout, too.

vwbill · Post by **vwbill** » Wed Feb 23, 2005 10:47 pm

This sounds like the dist is the problem or FI points; if you can put a backup in and get signal. Your dist is in all the way and you dont have a FI cam problem or the wrong Dist FI bottom cam like a rebuild I bought that was a different FI cam(different opening points) on the bottom shaft of the dist. I also had a problem when the top shaft clip came loose and let the shaft move. Do you get the Fi points to read when you turn the dist around the fire curve? Have you tested the resistance of the wires from the FI point connector and the ecu? Sorry I cant be anymore help! bill

wallacehartley · Post by **wallacehartley** » Thu Feb 24, 2005 12:00 am

I would be inclined to follow MGVWfan here for a bit, at least initially - the varnish and crap cant be good. It can't hurt to clean them internally at any rate, whether varnish is the root of your problem or not..........

kh · Post by kh » Thu Feb 24, 2005 1:05 pm

As for clogged injectors, I checked two of them and they seemed to squirt fine. I assumed the other two were the same since no activity from them either.

I 1st checked that an injector can handle 12v. Then I experimented with
an old injector and touched it with 12V from a spare battery.

The test injector clicked normally. The injectors on the car, I left on
the fuel rail and stuck them through the lids of some clear vials that
remind me of urine sample cups.

I hooked test leads to one of these injectors and from a safe distance
energized the injector with 12V from my spare battery.

Out came a beautiful cloud of atomized golden go-juice.
I didnt try this on all 4, but assumed the same since no activity from
them either.

In fact, the original 4 injectors that I removed from the car years ago wont fire when plugged in to the car either.

I only used the spare distributor as a lazy way to stimulate the injectors
without cranking the engine and independent of my tester.

It is my humble/ignorant belief that cranking the engine, using my tester,
or using my spare distributor - all exhibit the same symptom - No injection fire.

But this car has sat for 5 years. I am the 2nd owner and bought it here in San Diego circa '81. I drove it for a few years but by 1990 neglect had taken its toll. Back in 99 I resolved to get this car back on the road.
I replaced all hoses, injectors, tune up parts etc.
She ran pretty good, but a bad master cylinder stalled my momentum.

Blink and fast forward 5 years. I guess STA-BIL doesnt cut it for this
long. Drained and cleaned the fuel system best I could but my beloved expensive new Bosch fuel pump is gummed up or dead forcing me to retreat to a stand-by. I then went through hell unclogging my return fuel line to get the pressure under control. My poor regulator moaned but all my new hoses held.

In theory, I checked MPS, CHT and trigg points.

thanks again!

vwbill · Post by **vwbill** » Thu Feb 24, 2005 2:37 pm

I know this is frustating! You have pulled the Throttle position switch on the throttle body and cleaned and adjusted it? If you said the injector signal is fine with your backup dist and they fire in pairs and you are moving the throttle to get this signal and you have tested the injector and they are in working order. So you have working injectors a temp working dist with good fi points and the ecu works with the backup dist so the grounds seem to be good for the injector what do we have left guys? If the pump is working doesnt that mean the tps is working. So what is different in these situations. It seems to be the dist. too me. You seem to be saying the injectors work fine with the backup dist. and the ecu is controling the pump when you move the tps so I'm guessing that is telling the ecu to fire them if they work with the backup. I'll have to read my fi book, where is that darn thing! You'll get her with the help from the other guys! bill

raygreenwood · Post by **raygreenwood** » Thu Feb 24, 2005 3:19 pm

The ECU does not control the pump really. It is a simple timing circuit that buzzes the pump during the first bump of the key. The TPS will have nothing to do with the startin. In fact...you can disconnect it while idling with no change. This sounds like a trigger problem. You should remove the dizzy.....pull, clean and check the triggers, then with the VOM connected to the triggers, turn it by hand checking that each of the points is opening and closing by electrical check. Then pull the points plate out of the dizzy..and look at the cam. make sure it is not rattleing and loose on the shaft. Make sure the plug on the dizzy is making a clean connection. Ray

kh · Post by kh » Thu Feb 24, 2005 5:25 pm

Begging your pardon, I am a long term 412 owner and have a stack of documentation. Im also equipped with a trunk full of spare parts but alas, only a shot glass full of experience and a thimble full of common sense.

My understanding is that the ECU does control the pump after start.
That is what I thought I was simulating by turning my standby distributor by hand with the contacts connected. I had already turned the key to start and then left on. The pump was apparently energizing out of phase with injector pulse when I turned the spare distributor by hand.

Two distrubutors with trigger contacts that <I think> check out, show
the same symptom.

Also I concluded that they really dont have anything to do with the quality of the signal to the injectors - just the existence of it.

Perhaps I have not sufficiently proven that signal quality to the injectors is
my problem. My theory is that I have consistent injector signal, but it is
not of sufficient amplitude to satisfy the injectors.

The only thing that I could imagine would affect signal quality to the injectors are ECU, injectors, the wire between them and a common ground.

8 injectors apparently not firing when hooked to the car, but 3 those proven to trigger if hooked directly to 12V.

Howzabout those injectors. I dont have them with me to confirm the part numbers but they were all the same. Yellow with pressed on straight nipples. I think they are 0 280 150 044 but I see Anders shows 0 280 150 009 for a 1.7 914. Any difference in input sensitivity?
My circa '72 parts book shows vw #311 906 031B. I have some other
injectors that came off a 914 that I have not tried, I believe 3 were 009s but one was an odd 005.

vwbill · Post by **vwbill** » Thu Feb 24, 2005 6:12 pm

Hey The ecu does regulator the time and duration of the opening of the injectors. I was reading the book and got the thought when its says the operation of the starter motor is sent to the ecu! Do you think the wire coming from the starter could actually be causing a problem? It does say the duration is also govern by the engine speed and load and sensed at the dist contacts(the timing of the inj are contrl by the dist points) and reported to the ecu. The load is sensed by the MPS at the intake. It seem from the book that the TPS shut the fuel supply when the throttle is closed and the engine speed is high (over 1800) then back on under 1250. It does request more fuel from the ecu when the pedal is pressed calling temp enrichment or inj timing. then it says on some eng. if the pedal is at full or certain spot a certain amount of fuel is injected. I'm confused with what the ecu does when the TPS(TVS) is disconnected? I'll scan and send what my book says in a little while but I had my laptop drive crap out so I'm working on my older luggable,lol! Sorry you're having such a epic problem! I wouldnt have gonna my to turn over with out the guys here.! Bill

kh · Post by kh » Thu Feb 24, 2005 9:52 pm

Well I believe its ECU pin 18 from the starter/solenoid.
I thought this could be the problem when I didnt think I was getting
any signal to the injectors. I was only showing 11.7 to the ECU.
Figured a remote start switch would test that theory.
Didnt help. I ended up putting one of those low voltage relays on
the starter to rule it out for good.

Having said that, I thought I proved long ago that the car will run with this terminal grounded.
The cold start wont fire in San Diego anyway, I dont think.
Everything I read now says the car wont start without this signal from the
starter.

As for the TPS, dont know. I had ruled it out as a potential solution so
it is the one thing I have not looked at. I do have a spare.

I believe a disconnected MPS and CHT cause an ultra rich condition so
should be able to disconnect the TPS,MPS & CHT since Im on the bone dry
side of lean.

wallacehartley · Post by **wallacehartley** » Fri Feb 25, 2005 3:19 am

I am gonna be honest and admit that I am here to learn about these cars. My plan is to prep one and take me, my beloved and our 2 youngest men and drive up to say, Dar es Salaam, or Nairobi at least. What I am reading here illustrates to me the value of building a second ecu into the other side of the car as a back-up unit. It would be useful in testing as well.

Are we certain that the ecu doesn't await a signal from a sensor somewhere; say crankcase temp or CH temp, before attenuating to the 'jectors to fire?

What are all the sensor inputs? How many and from where? What should that signal look like? Can we get a successful firing test by bridging sensor inputs, or attaching VR's to the ecu?

Has anyone a list of all sensor inputs and what they should measure out at?

Why not design a test routine, perhaps even a jig, to test and fault-find these systems? And we can leave it here on this thread, for future reference?

Can you detect my German Engineering ancestry?

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