Dan Martinic

Good work! Now, did you move or touch anything during that half hour rest?

Jacob AbuKhader

Nope. I had no start condition with both ECUs and wanted to double check voltage to the injectors so while the car would crank and not start I measured it. After about a half hour the car will start again with either ECU installed so that’s what I did. I measured voltage again once it started up and ran.

Another weird thing, during a nostart I started cranked the car over with one injector plugged in and the car actually started. Same story with two injectors. But 3 and 4 plugged in and the car just cranked again.

It seems there’s a voltage drop somewhere so now I have to wait for the car to stall again and try to find the drop.

Another anoying thing my interior lighting all shorted without my fuse popping and now my oil pressure gauge isn’t reading anything. I don’t get why the fuse isn’t popping it’s the correct amp fuse.

I hate electrical gremlins.

Dan Martinic

Oh my.

Your experiment: was it two injectors worked, all four plugged in didn't? Or, was it one and two plugged in worked, then three and/or four by themselves didn't?

Try plugging in #1 injector wire into only number three or four injector and see if the behaviour is the same (ie. starts like only number one injector is plugged in)

In other words, try and see if the above behaviour is related to injector harness wires three and four or injectors three and four

Dan Martinic

I am also wondering if it's possible that the load of three or four injectors plugged in vs just one or two is having an effect on some failing component. I hope Peanut or someone knows the relevant component or driver

Grant Coles

This is from Clarks garage on the fuel pressure regulator "Testing Without question, one of the best checks for a faulty FPR is to check the fuel pressure at the rail. If you have access to a 0-100 psi fuel pressure gauge , check the fuel pressure at the rail using FUEL-01. Normally a faulty fuel pressure regulator will result in a very high fuel pressure. So, if your fuel pressure is well above the specs provided in FUEL-01, you probably have a bad FPR.

One of the most common failure modes for the FPR is to fail closed to the point that fuel rail pressure is extremely high. The high differential pressure across the injectors causes them to draw excessive current. The excessive current is seen by the injector drivers which subsequently shutdown. If you have a condition where the car will not start or starts and almost immediately dies, try disconnecting the wire for one (1) injector. Attempt to start the engine. If it starts and continues to run, the fuel pressure regulator is likely bad. Bear in mind that running on only three cylinders, the car will run very rough. By disconnecting one injector, it reduces the current enough to keep the injector drivers from shutting down.' Could this be your problem? The thread is too long to go back and see if your fpr has been tested

Dan Martinic

That's an excellent suggestion Grant.. but he does have a permanently installed FP guage and last we heard, it's been showing normal FP. However, the relationship between the injector driver(s) (they are batch fired so could be just one?), the wires, and the injectors or one of those could be it. There are dramatic differences when changing ECUs

Jacob AbuKhader

Apologies everyone. I’ve spent all day trying to get my interior lights working again with zero success. I repaired the headlight switch only to have the same thing happen again. Now I have to pull apart the entire dash again.


Dan the test I did was two injectors started the car all four didn’t. I had it running for about an hour while working on it and it finally died while idling. Something is getting hot/ causing a voltage drop.

And yes my fuel pressure regulator is new and yes my fuel pressure is testing normal. I’ll head back out right now and see if it will start and try plugging and unplugging the injectors randomly 2 at a time and see if it starts

edit: confirmed, doesn’t matter which two injectors are plugged in it always starts with 2 plugged in. 3 or more and the car just turns over doesn’t fire.

Jacob AbuKhader

Okay so more no start conditions today. I tried junketing the car again both ways and same results. Terminal 30= no start but running pump, terminal 86= running car.

Is there any DIRECT correlation between terminal 30 on the relay block and the supply voltage to the injectors.

Either the transistors within the ECU are failing on both, there’s another chip that drives the injectors that’s fried in both ECUs, or there is a voltage drop somewhere from the relay block to the injector plugs within one of the ICs on the digital side of the motherboard or analog side of the motherboard or within the actual wiring harness itself. The ECU harness is brand spanking new but the accessory harness is 36 years old. Just because the wires don’t look burned up doesn’t mean something fishy isn’t happening.

How can i test the ljet electronic ignition system with a load applied to it. A meter won’t pick up a voltage drop I need to add a load in the form of a bulb to the circuit

Jacob AbuKhader

okay fellas. What do you make of this?

peanut

Power to the injectors is supplied by the first DME relay and is constantly hot whilst the ignition key is switched to on.

Unless there is a short or a poor connection to the injectors the issue is more likely to be at a ground point because the injectors are pulsed 'fired ' by the ECU which internally grounds the injectors to complete the circuit.

This injector ground pulsing lasts around 2-15 milliseconds long depending on the rpm of the engine and the engine load ,temperature etc .

Usually when the engine will start with 2 or 3 injectors connected but not with 4x its due to excessive fuel pressure . Disconnecting 1x injector is a common diagnostic test for a over-rich mixture or non starting engine.

However as this ECU supplies a separate ground to 2x pairs of injectors within the ECU and it will start with 2x but not 3x injectors , it does suggest that their is an overload issue within the ECU on the grounding chip.
This could be due to high resistance at one of the ECU ground points or a connector somewhere

I have maintained all along that as there could be a fuel pressure issue you should buy a proper fuel pressure guage and connect it to the fuel rail so you can get an accurate fuel pressure reading and response instead of the mickey mouse guage fitted to the car

What you might try is to start the car with the Injectors connected to cylinders 1&2 then try connect one of the other injectors 3 or 4 and see what happens.
Then do the reverse . Connect injectors 3&4 and start the car then connect injector 1 or 2 and note the difference in response.

This might isolate the issue to one bank of Injectors 1&2 or 3&4

Jacob AbuKhader

Peanut thanks for the info. I did what you suggested and it didn’t matter, both sets of injectors started the car, just not all four plugged in.

1,3 started and 2,4 started but all 4 plugged in and it was back to cranking endlessly. Same story with only 3 plugged in..

If you don’t trust my fuel pressure gauge the tech at the dealer measured my fuel pressure when it was there and reported that my fuel pressure was normal.

Pulling one injector does not start the car it has to be two.

The 2 volt readings on everything has me very confused. When I previously measured my injectors they had 12 volts.
Same goes for my ignition coil. How are they even functioning at all with 2 volts?

peanut

they arn't !
you cannot measure the voltage of the injectors with a multimeter whilst they are working .

You need a occiloscope to show the injector voltage whilst firing

As I have said previously they are grounded by the ECU .
Even on idle the injectors are firing 900 to 100 times a minute (once every crankshaft revolution)
A multimeter isn't capable of indicating voltage at that speed.

The grounding of the injectors is done internally by the controller chip in your ECU the one your friend replaced.
They are injector specific as all injectors have different resistive values . Wouldn't surprise me if you have the wrong controller chip or injectors

I said the injectors are fired in blocks of 2 ie cylinders 1&2 and 3&4 .........so you go and test injectors 1&3 ? why did you do that ?

if I ask you if you have cleaned all your grounds I bet you'll tell me of course I have but if I were to ask you which specific ground points you cleaned that are used by the ECU to ground the Injectors you probably wouldn't be able to tell me.

Please try to read all what is written and try and answer all questions even if they don't seem relevant to you ,otherwise it is very difficult for people to help you from a distance

Jacob AbuKhader

I should have been more clear. I did not start the car unplug the injector harness and try to measure 12 volts. I turned the ignition on and measured each side of each plug. It should be 12. I read 2.


The ignition coil should also be supplied 12 volts via the black and green wires. Again you can see in the video it reads 2 volts. I asked because I have read 12 volts before on the ignition coil not 2.

I cleaned the ground on the bell housing, I cleaned the ground up front by the driver side headlight, I cleaned the grounds on the rear by the tail light housings and I cleaned the ground underneath the fuse/ relay block.

Ill unplug the injectors again. I tried unplugging it in the batches they fire in. I thought they fired 1,3 together and 2,4 together. Not a big deal I’ll just try it again correctly.

Jacob AbuKhader

So i managed to get my hands on another DME. This one hasn’t been meddled with in anyway. My car has run perfectly for now 3 days straight, with over 30 miles without a stall, and over 1.5 total hours idling. I never made it that far with any of the other DMEs they certainly wouldn’t have lasted this long without a stall.

As for the voltage readings, turns out my meter was busted. I double checked all my voltages again (again the correct way) and sure enough I do in fact see 12V where I’m supposed to.

As far as pulling the injectors go, I haven’t had to do this because, the car hasn’t stalled.

So good news!

Im not going to call it fixed just yet. I’ll post back when I’ve hit over 100 miles without a stall. So far though it’s looking peachy.

Dan Martinic

How many thirty-plus year old DMEs does it take to fix a voodoo running issue?

One. A good one. LOL

Broken multi-meter? That's a new one.. never think to check if they're working properly or not. Good luck and I hope that's a wrap on this!