V8 fuel injectors.

**Konradical** · 7th November 2018, 12:01 PM

So the joy only lasted half a day.

Then I spent the other half pulling the loom apart looking for something hidden. And guess what? It is tight.

Unplugged the thermotime sensor and I could get the new ECU to run without the fuel pump. Add fuel pump and it stalled. With the sensor plugged back in, and a near half tank of fuel it now starts as it did on the new ECU.

Tracing the diagrams, only the crank signal to the ecu is on that circuit. The thermotime switch operates the cold start injector which I have isolated.

From memory that switch earth's out initially then disconnects the cold start injector circuit after a predetermined time or temperature... I am wondering how all of this goes together.

**LRJim** · 7th November 2018, 01:27 PM

Originally Posted by Konradical

I am wondering how all of this goes together.

Rubber bands, chewing gum and hope.
Good luck with your gremlin!
Cheers Jim

**Konradical** · 7th November 2018, 01:31 PM

Originally Posted by LRJim

Rubber bands, chewing gum and hope.
Good luck with your gremlin!
Cheers Jim

May have to be a sneaky tow rope from the D4, under the van to ol Rangie I reckon.

**Konradical** · 7th November 2018, 10:29 PM

Here's a question for you.. when hot, what components of the Flapper EFI could completely shut down the engine?

Not a cough or a splutter, just off.

So I have ruled out fuel pump or pump relay. There is pressure there when asked.

There is spark, so that rules out ignition module (been modded), coil and everything up to the plugs.

The coolant temp sensor is 400ohms, measured at the ecu plug and the sensor.

The only things I can currently think of are thermo time switch, which is only in the initial cranking circuit, engine speed signal wire, TPS and AFM.

I'm getting an engine signal, so that's out.

I do know the injectors aren't firing as the fuel pressure remains constant when engine is cranked.

I have replaced the terminals on the earth wires behind the LH head just in case. They test as 0.5ohms at the ecu plug to body ground. I have also tried running seperate earth's to no avail.

Today I found if I could cool down the ECUs, they would start and run fine. Both of them. Once the engine cut out for whatever reason, I could only use the original ecu without the fuel pump to get me moving.

With help of mate(2700km away via WhatsApp) we identified some dodgy looking parts on one of the ecu boards. I also noted that there was no heatsink paste where they mounted. I fixed what we thought was dodge and used toothpaste as a temp heatsink paste.

They both only ran for about ten ish minutes. Then cut straight out.

Again, it doesn't cough or splutter or surge like something with too much fuel or running out, it just dies.

**Konradical** · 8th November 2018, 06:05 PM

So again with the help of my mate, a ton of photos, a copy of the information I have and WhatsApp, we managed to identify the main 5V transistor as a possible issue.

From his reading, one not skewed by reading it a million times, he managed to find something along the lines of "dry joints in the solder can emerge over time from constant thermal cycling and if the main 5V transistor has these dry joints, the engine will die suddenly".

After a bit of close inspection, it was possible that there were some possible signs of this in the emitter leg of the main transistor. Agriculturally I applied some more solder to these areas.

On a test run for over an hour, it seems to be holding up. Will take it for another run later after servicing the AC and see how it keeps going.

Hopefully this is the end of this drama and this thread from your forum feed.

**4bee** · 14th November 2018, 12:12 PM

Tooth Paste you say? Should look nice & sparkly when you take new photos then? Maybe it is the Fluoride as it seems to be a good heat transfer medium ?

Now you can appreciate what your determination can do. Well done, fingers crossed.

**Mercguy** · 22nd November 2018, 12:41 PM

Originally Posted by Konradical

So again with the help of my mate, a ton of photos, a copy of the information I have and WhatsApp, we managed to identify the main 5V transistor as a possible issue.

From his reading, one not skewed by reading it a million times, he managed to find something along the lines of "dry joints in the solder can emerge over time from constant thermal cycling and if the main 5V transistor has these dry joints, the engine will die suddenly".

After a bit of close inspection, it was possible that there were some possible signs of this in the emitter leg of the main transistor. Agriculturally I applied some more solder to these areas.

On a test run for over an hour, it seems to be holding up. Will take it for another run later after servicing the AC and see how it keeps going.

Hopefully this is the end of this drama and this thread from your forum feed.

Sounds like Mercedes fuel pump relay-itis on w126's.... dry solder joints from decades of thermal cycling.

run over the entire board on the spare ECU with the soldering iron and swap them over. See if there is a difference. If so, do same for original ECU (rework/reflow). Old D-jet ecu injector drivers and trigger points suffer the same problems occasionally.

A second pair of eyes is always useful when you're at your wits end. It often prevents oneself from going bezerk with the reciprosaw and sledgehammer.

Hope the cure's permanent.

**Konradical** · 3rd December 2018, 07:20 PM

So guys, after a crazy few months of theories, testing, swapnostics and a few million gigabites of internet, I have managed to steer the ol girl through the centre of this land down here to the cold country. Obviously not without drama! That would be boring..

The main battery dropped a cell somewhere around Tennant Creek so needed to be jump started everytime. Poor second battery couldn't spin it enough (also ran the fridge with our food in it). Trans temp light now comes on as it feels like it, even though the temp isn't hot or trans slipping. Drop arm ball joint developed about 40years of wear and would get sudden death wobbles as you were cruising or trying to brake. Trailer indicators stopped working, fine on Disco, some voodoo in Rangie. RHR door doesn't open and that was where the chickens were riding. Tyres wore very quickly; this sort of surprised me as it wasn't hot, but then again I did fit them in 2011 so def due for replacement.

Golly gosh!

BUT, the original problem to this headache?

Dry solder joints in the injection circuits in the ECU(s).

Unluckily enough the "new" ECU that was given to me had these. It was ok at idle, but as soon as a larger current was required it heated the board and exposed tiny gaps, causing the breakdown of injection. Sometimes it would just miss due to lack of fuel, other times it would be hot enough to enlarge the gap to the point it wouldn't fire at all.

The dodgy soldering I did managed to fill some of these gaps, although revving it enough to propel the car past 80 was often a issue.

The original ECU we are thinking has a short to earth. It's either by the board or a dodgy transistor.

The ECU I got from Ebay magically arrived two days before we left and ran perfect the whole way down.

The plan is to send the original away to be repaired by someone who knows what's up, the new one we are going to have a play with and see if we can use a process to "melt" the solder back to it proper state.

Unfortunately to test the ECU for these issues requires at least an osiloscope and a variable voltage regulator to push the circuits through their paces.

I would suggest anybody with sudden cut out, overfueling, poor fuel economy and performance issues do a ECU swap before getting all crazy at throwing parts around and pulling out the last remaining whisps of hair.

Thanks you all for your patience, help and the space on your thread feed!

Konradical..

P.S. if anyone is having a similar issue and would like me to guide you through, don't hesitate to contact me.

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