E30 M52

[B C]

Having tackled the mess under the intake manifold last week I am now tackling the mess above the intake

The injector harness checks out good. (Huge relief!) Continuity and resistance on all connectors check out normal, and I even flexed/wiggled the harness while testing in case theres an intermittent connection.

As I checked the ground wire at the end of the harness I noticed a crumbly rectangular block encasing one of the wires. It had electrical tape around it. I removed the tape and crumbly block hoping to find a broken wire and an obvious solution but only found a resistor soldered inline with the ground wire as pictured above.

The resistor tested good, i do find it very strange that a ground wire has a resistor though. Mike, any ideas why this might be?

This leaves me with injectors themselves being bad (who knows, perhaps some junk in the fuel lines/rail jammed them up right away on first start) OR the ECU being bad.

I didn’t see any burned components inside the ECU when i took a look and no broken solder joints on the injector drivers, but I should have another ECU to try out sometime soon (thanks Kaiser!)

[HipMF]

You really took the wind out of my sails by posting the resistor value... Memorizing the resistor color code is one of the few skills I picked up at my last job.

A resistor in series with the injectors would limit current through then circuit. It's a bit of a mystery to me why they would want to do that, but my guess is that the DC resistance of the injector when it's on might be too low for the driver circuit.

Electrically, an injector is an inductive load. Inductance resists a change in current flow through a circuit. So, if you want to turn the current on and off very rapidly, you need to keep the inductance low. In practice, inductance, resistance and magnetic force are all related. So my guess is that to get a high enough magnetic force to open the valve of the injector (which has fuel pressure pushing it closed), and get the injector to open and close very quickly (which means changing the current flow very quickly), they had to lower the inductance (and in turn, the resistance) to a point where, when the injector is fully "on", the DC resistance is too low for the driver circuit.

Kind of shooting from the hip here, but that's my best guess. Putting the resistor in the harness instead of the ECU means you can change the injectors after-the-fact without having to rev up the ECU, not to mention that it probably generates a fair amount of heat...

[B C]

[emoji16] I knew you would have the resistor color codes memorized.

[HipMF]

Yep, I used to program, run and maintain a Universal axial inserter.

She was a blast from the past. The computer that ran the thing was the size of a microwave oven and only slightly more powerful than a Commodore 64 (not even exaggerating). Crazy high-tech stuff by late 80s standards, but I left tech school in 2011...

[GunMetalGrey]

I'll have to double check the harness I have laying around, but I don't think I've ever seen a resistor in the injector wiring. 
In regard to your throttle bodies, I'm not sure how to connect the throttle cable to those, I believe those types used a ball end instead of the kind you are used to.

[B C]

GunMetalGrey said:

I'll have to double check the harness I have laying around, but I don't think I've ever seen a resistor in the injector wiring. 
In regard to your throttle bodies, I'm not sure how to connect the throttle cable to those, I believe those types used a ball end instead of the kind you are used to. 

The gray block in line with intake runner #3 is the resistor is. The gray encasement is some sort of clay or ceramic

[Jdesign]

HipMF said:

You really took the wind out of my sails by posting the resistor value... Memorizing the resistor color code is one of the few skills I picked up at my last job.

A resistor in series with the injectors would limit current through then circuit. It's a bit of a mystery to me why they would want to do that, but my guess is that the DC resistance of the injector when it's on might be too low for the driver circuit.

Electrically, an injector is an inductive load. Inductance resists a change in current flow through a circuit. So, if you want to turn the current on and off very rapidly, you need to keep the inductance low. In practice, inductance, resistance and magnetic force are all related. So my guess is that to get a high enough magnetic force to open the valve of the injector (which has fuel pressure pushing it closed), and get the injector to open and close very quickly (which means changing the current flow very quickly), they had to lower the inductance (and in turn, the resistance) to a point where, when the injector is fully "on", the DC resistance is too low for the driver circuit.

Kind of shooting from the hip here, but that's my best guess. Putting the resistor in the harness instead of the ECU means you can change the injectors after-the-fact without having to rev up the ECU, not to mention that it probably generates a fair amount of heat...

At that, if you said the harness tested alright, and you check the injectors, I would say the ECU. I ran into a similar scenario and it was bad capacitors inside the ecu. Old aged  potting material seeping or cracking out would cause super random injector feed issues. Sometimes only under load.

[B C]

“Why do I need a compruter? What does a compruter look like? What does a compruter even do?

I dunno

Who cares?!?

For your swap, ya dangus”

[Jdesign]

Snap said:

“Why do I need a compruter? What does a compruter look like? What does a compruter even do?

I dunno

Who cares?!?

For your swap, ya dangus”

That was almost more hardest to read that of my post above yurs.

[B C]

[KaiserRolls]

For your health

[B C]

Chapter 15: The wild goose chase

Cliff’s Notes: was running on 4 cylinders, determined 1 coil is bad and 1 injector was stuck. Injector un-stuck and now running on 5 cylinders until i get a new coil

Kaiser is a good guy. He sent his ECU for me to try out. After plugging it in I expected to fire it up and hear all 6 cylinders running. But it still ran on 4.

The last piece of the puzzle should be the injectors.

The misfire was on cyl 2 and 3 so i moved those injectors to 1 and 4 and sure enough the misfire followed.

I felt a bit ripped off since back in july when i bought the engine they were working fine and i had sent them off to be cleaned and tested by a reputable injector shop.

I pulled the bad injectors out as well as 1 known good one for reference I checked the resistance. All were good at approximately 14 ohms.

So i connected the injectors to a 12v power supply (jumper box) and checked for solenoid clicking.

The good injector clicked, one of the “bad” injectors did not. I kept applying voltage and it suddenly started clicking. All 6 injectors were now clicking when manually applying power to them. So I put the injectors back in and expected to fire it up and hear all 6 cylinders.

Nope.

BUT WE UPGRADED TO RUNNING ON 5 CYLINDERS

So i checked the remaining “bad” injector. Hmm it isnt bad at all. It ends up being a bad coilpack even though I bought all 6 brand new, Bremi brand (OEM). Moving it to other cylinders as well as a resistance test confirmed it was bad. It measures 40 ohms on the outer 2 pins when a good coil should be

Now in hindsight it can see that the 2 dead cylinders were from 1 stuck injector and 1 bad coil instead of 2 bad injectors as originally thought.

I just need to replace the coil and I should be in business

5 out of 6 aint bad

[YoungCR]

I've heard bremi coil packs can be duds from the factory, glad it's getting sorted out.

[B C]

Good to know its not just me. I dont have a lot of faith in the remaining 5 as a result

[Jdesign]

Snap said:

Good to know its not just me. I dont have a lot of faith in the remaining 5 as a result

I spent more time than most humans should researching brands and coil information. I hope the new coilpack has you running smoothly.

[B C]

Much better!

All is now well in the world once again

Gunmetalgrey sent some old coils with the parts I purchased from him and swapped out the one I tested that was bad

[YoungCR]

Woot WOot!

[Jeff]

Nice! But where is the burnout video???

[Jdesign]

This^^^ Glad to see its alive and well!

[GunMetalGrey]

Purrs like a kitten! 
Glad it's firing on all cylinders!