L Jetronic adventure - injectors not firing

[mark 74 carrera]

Ideas for my next step would be appreciated. Here's what I have done so far.

Bought a car that had been sitting but was running before it was parked. With help from this forum, I got it started and running. The car turns over now but does not start. I was driving it and went to restart after fueling and it wouldn't start. Things I have done:

Searched and read just about every source and post on the L Jetronic system and I have the PDF on the system
Replaced all fuel lines except center tunnel line
Replaced cold start valve (previous one destroyed during removal of old fuel lines)
Replaced fuel pump relay (mounted under battery)
Checked and confirmed injector ground attached on coil
Tested fuel pressure and confirmed at fuel rails (so not a fuel delivery problem)
Replaced all vacuum lines
Tested spark at coil and spark plugs - confirmed at both locations
I will test for power at the injector plugs this weekend (if there is no power, what would be the cause?)

Using a syringe, I placed gas in two cylinders and engine sputters and tries to start until fuel is consumed. So, I know I have spark in cylinders. I am pretty sure that the injectors are not firing. I doubt all four injectors failed exactly at the same time. I think I'm down to the ECU or a sensor that is no longer working. It seems to be an electrical issue that is causing a lack of fuel. What sensor would prevent the ECU from sending signals to the injectors to fire? Is there something else that I might be missing?

Any help would be appreciated, Mark

[Dave at Pelican Parts]

I'm glad to see that you tested for spark, that is often overlooked!

The "dual relay" that hangs off the battery tray sends power to the resistor pack, which is nearby. The power then goes to the injectors the whole time the key is on. The ECU ("brain") provides a ground to the injectors to get them to open, then disconnects that ground to get them to close.

Check for power at the resistor pack. Check for power at the injectors. (It'll only be on one of the two pins in the plug, obviously.)

If you have or can locate a "noid light", you can hook it up across an injector connector to see if the injectors are getting any signal or not. You may also be able to check the non-powered pin on an injector plug to see if it gets a ground and disconnects while the starter is cranking. Many meters won't be able to read a quickly-changing pulse like that, though, so not finding that ground is not definitive.

The white wire from the injection system needs to be plugged into the coil (-) terminal. That tells the injection when to open the injector valves. I think that if the air flow meter is unplugged, the injectors will not open as well, but I am less sure of that.

In general, a vacuum leak will not prevent the injectors from opening at all but will make the mixture lean enough that the engine idles poorly or will not run at all. This is the main thing to check for if you do have some signal going to the injectors.

--DD

[mark 74 carrera]

Thanks Dave. As always, great input. I will not be able to test further until next week but I will update the thread when/if I find the culprit.

Mark

[mark 74 carrera]

I have replaced the resistor pack (It broke when I removed it) I have 12 Volts at the injectors. Both the voltmeter (showed 12v) and the noid light showed voltage with key on. I tested with noid light and could not see a pulse, so it may not be grounding. I watched the light very closely and it burned steady with not a hint of a flicker.

So, am I left with just the ECU as the possible culprit or is there a sensor that could be bad and preventing the ECU from sending the ground signal? I feel like I am close to finding the problem. Plus I have checked the health of the whole fuel injection system, the fuel flow and the vacuum system. Now, if it would just run again.

Any suggestions? Mark

[mark 74 carrera]

I checked into having my ECU refurbished. $100 diagnostic fee and then another $200+/- to refurbish if needed. I decided before I do that let me see if I can find an ECU for sell. Bought one off ebay for $75 plus shipping.

Installed the used ECU and the car immediately fired up. So, it was the ECU. Now, we'll see how long the car decides to run in its current condition. Thanks for all of the help provided, I learned a lot about the L Jetronic and in the end won the day.

I still have oil leaks, brake adjustments, interior and lots of other stuff but I can drive it around now!

Mark

[mark 74 carrera]

What might be the causes of a car stalling after it is warmed up? The car starts immediately every time. I drive it around the neighborhood on the weekends to keep the battery charged. But after it has warmed up, it stalls at stop signs. It will immediately start right back up and I'm on my way.

Idle right after a cold start is about 850 rpm and is steady with no sputtering. I never did have the injectors serviced. Could the spray pattern be bad enough that after the cold start valve senses engine temp warm that the injectors don't atomize the fuel enough?

Should I just raise the idle? What's the best way to do that?

[pgeorgeson]

Dave (or someone). Dumb question, but where is the resistor pack (1973 2.0)? I have no power at the injectors, but I can't find it to test upstream.

[Dave at Pelican Parts]

The D-jetronic system used on the 1.7 and 2.0 914s does not have a resistor pack. That is specific to the L-jetronic used on the 1.8 liter cars.

D-jet opens the injectors the opposite way from L-jet. D-jet leaves the injectors grounded all the time, and the ECU sends power to them to open them. If you never have any power to them, the ECU is not sending any. The ECU may not be powering up (does the fuel pump run when you turn the key from off to on?) or it may not see that the engine is turning, or it may be something else.

First thing is to check for unplugged or broken wires and hoses.

--DD

[pgeorgeson]

Dave,
I guess that explains why I couldn't find it anywhere. Fuel pump is working and I am getting fuel pressure. I am also getting spark. I put a test light (and multimeter) on the injectors expecting to get pulses, but didn't get anything. I did search for broken or unconnected wires but didn't find anything. Now I am wondering about the crank position sensor. Are there any other sensors that come into play?

[Dave at Pelican Parts]

There is no crank position sensor.

There are FI trigger points in the base of the distributor that tell the injection when the engine is turning over, and how quickly.

Just to make sure--the pump runs for about 1.5 seconds when the key goes from "off" to "on", and then stops, right? Or does it run full-time? If the latter, someone has been mucking with the wiring and you need to figure out what they have done.

--DD

[pgeorgeson]

Thanks Dave. I had to chase down CPS issues on one of the other cars, so I just assumed it was the same. You are correct on the fuel pump. It turns on briefly with the key until the pressure is built up, then stops. Is there a way to check the FI trigger points? I would note that the car was changed over to electronic ignition by the PO. Any potential connection/relationship there?

[Dave at Pelican Parts]

FI trigger points are completely separate from the ignition points. There's a 3-pin electrical connector on the front of the distributor near the bottom where the trigger point wires plug in.

It's a bit hard to test them. Best is to use an oscilloscope, but that's not a common piece of equipment. If your multi-meter reacts very quickly, you might see the pins getting grounded, but many meters don't read quickly enough for that.

--DD

[Jrboulder]

I'm pretty sure 914 L-jet uses the ignition points(coil) for FI trigger. It certainly does on my 912E.

Edit: the 1.8 FI wiring diagram shows a wire going from the ecu to N1 which is the coil. Same as the 912E.

[Dave at Pelican Parts]

Jr, we wound up with two different conversations in this thread.

It started as a discussion of the L-jetronic FI used on the 1.8 liter 914s (and the 912E), but then was morphed to a discussion about the D-jetronic used on the 2.0 (and 1.7) liter 914s.

You are quite correct about L-jet using the ignition points to tell the FI when to open the injectors. In fact, it opens all of the injectors at once. D-jet, however, uses the trigger points in the base of the distributor.

I would suggest that pgeorgeson take a look at Brad Anders' D-jet bible to see if he can figure out why his 2.0 system isn't opening the injectors: http://members.rennlist.com/pbanders .

--DD

[Jrboulder]

Oops, didn't notice the hijack. I found it hard to believe one of the world-class 914 experts didn't know that!