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Injectors not firing on BMW E30 4G63 swap, MPI related?

CarRacer

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Backstory: Complete motor setup has run in a previous vehicle and I've driven the current car recently. I idled it for a while two weeks ago and the next day it wouldn't start. I have tested and have power to the injector plugs, the injector plug ground wires have continuity to ground, and I have power to the CAS.


I'm running into issues with the BMW engine swap, I have spark (after manually closing the relay) and ~42 psi of fuel at the rail but it will not fire. I believe the issue to be centered around the MPI relay. I removed the cover on the relay, after buying a replacement, and used a small zip tie to close the left coil. This allowed the engine to fire on starting fluid. I then put a zip tie on the right relay to see if that would get fuel to the motor. This didn't work but touching the coil with my hand (I was trying to get the zip tie to hold the relay closed) and it fired. I could only replicate this solution once. I got pissed and removed the relay to jump wires in the plug itself. This didn't solve the problem either even after confirming power to the injectors and testing spark at the spark plugs.

I'm at a loss as to what could be causing this or what to research next. The setup has functioned in this chassis recently but now it doesn't. The few times it has fired after encountering this problem I have no idea what I changed to fix things.

Thanks for any help.
 

MellowVR4

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Try to remove the CAS and manually spin it and hear for the injectors clicking.
 

Dale

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Jun 18, 2014
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Brisbane, QLD
Are you sure it's related to fuel injectors? Have you checked coolant temperature sensor? Has the car been parked for a while? Bad fuel maybe? Loose ground cable somewhere?
 

CarRacer

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The car has been parked for a while, I just put 5 gallons of fresh 92 in it. It had barely any fuel in it so I was able to hear the rail fill. I put a few extra grounds from the motor to the chassis. Coolant sensor is plugged in and wires are in good condition. I'll have to try manually spinning the CAS, any other tests I can do?
 
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jrtech

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Feb 18, 2012
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Injectors are a ground side switched circuit controlled by ECU. MFI relay supplies +. We need to figure out why the ECU isn't grounding the injectors.

Your specific Crank Angle Sensor has to function @ least intermittently if you have spark. A good one rotating should have 5v pulse from the signal wires. I would look harder at this before condemning other parts.



 
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CarRacer

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Yeah, I had a test light hooked up and fired it a couple times on starting fluid to confirm spark. So the CAS is doing something.

I'll check that diagram today. I haven't read .org in a while and am glad this place is still cool, very helpful tech info supplied on a picture with a dick drawn on it.
 

CarRacer

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ECU wire 107 does back trace to the MAF sensor. I'm going to assume that isn't the problem, I'll try spinning the CAS by hand next.
 

CarRacer

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Maybe the ECU is sh*t? There's slight corrosion behind the eprom chip on the board. The capacitors seem to be in good shape with no acid leaks but I'm not so sure about the rest.


 

CarRacer

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When spinning the CAS manually I have no 5v signal at the ECU plug on either pin 21 or 22 with the key on, I can't hear any injectors clicking either. I also checked resistance on the injector resistor pack (I think I had the right ohmmeter settings) and everything measured zero to pin 3. I presume that means it is bad as it has no resistance.

At this point I'm leaning towards the ECU of the injector resistor pack being bad? I dunno, I'm so lost and out of sorts that I'm basically guessing at this point.


 

jrtech

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Have you checked the ECU for diagnostic codes? Sometimes it will show a ECU fault code. Seeing as how you monkeyed with the MFI relay there should be several stored codes @ least. If you have 12v at ECU, 5v signal from CAS @ the ECU, you COULD shotgun a ECU @ it. Do you get the "check engine light" when you turn the key on, then it goes out after a few seconds?

Edit: You little boogerbutt. Posted while I was curating a post.

If you have 12v coming into the CAS you NEED to see that 5v signal coming from the ECU. If you check the ground circuit integrity @ pin 4 and it's good. And pin 1 and 2 have 5v to the ECU. You can throw a CAS @ it. I am going to check my car right now to be certain what I am telling you about the 5v signal is accurate. EDIT:[CAS signal output to the ECU, you can't read it without a high-end multimeter or oscilloscope.]


If somehow your resistor pack went bad you can measure the impedance of your injectors to make sure they didn't take a hit. Also you need the smallest Ohm scale to measure the resistor pack. You are measuring single Ohms here.
 
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CarRacer

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So...that's the thing. The diagnostic post isn't hooked up in the chassis. I was going to wire it in but that is basically only to get a logger connected but I have no way of writing to a palm pilot with my current PC setup.

I'm of the opinion that the CAS is bad.
 

jrtech

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Signal wires pin 1 and 2 @ CAS should have 5v reference from ECU at KOEO. Do you have that?


If not then you have a problem with your ECU. You can check other pins @ the ECU that should have 5v to see if it's a localized problem or the whole 5v rail.
 
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CarRacer

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Well now I don't have 12v at the CAS with KOEO. I give up for tonight. I'll be back at it early next week. Your help in spoon feeding me information is majorly appreciated.
 

jrtech

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The MFI relay supplies the 12v rail at the ECU, which means no 5v either. So maybe you are onto something with your power supply issue. Come back to it with fresh eyes and maybe you will catch something you missed.

Edit: Take pics of that MFI relay so we can inspect the solder joints and relay contacts.
 
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OldHairyBastard

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Look a little closer. It looks like you have two caps that blew. The one by the injector board and the smaller on at the top. Take a good look with a magnifying glass to see all around those areas.
 
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jrtech

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Good eye OldHairyBastard!

Not to hijack, but are there any documents floating around for the ECU board layout?
 
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