New Install M20: Only 3 cylinders despite solid connections. Resolved

[gybe,]

This has been resolved. Issue was three of the six brand new "flow matched" injectors don`t actually flow. They ended up on the same elctrical harness and they all diagnostically tested like they were operating (internal solenoid would energize/click), but the valve was not actually allowing fuel to flow through. So, even if everything says that the injector is functioning, if you haven`t seen it actually flow fluid, you can`t be certain.

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I just swapped in a freshly rebuilt m20b25 and after going through some fun to get it started (had oxidation in the harness preventing one bank of fuel injectors from firing), I have now encountered my next bit of fun....car fires right up, cold or warm, but runs very poorly. The particular symptoms are a fundamental lack of response to throttle input (very slow to rev), no power, and general "rough" running. Idle seems a little rough, but it doesn`t "hunt" or fluctuate. It is tough to actually say that it is rougher than I would expect as the car is a stripped and prepped race car, so everything is a bit loud and rough. Under attempted acceleration, the car does not give any indication of wanting to stall, it just does not deliver power in any appreciable manner. Revs will climb, but are very slow to do so. I did have one instance of what seemed like fuel cut when I got it above ~4500 RPM on an incline.

As part of my prior no start issue, I have already done a fair amount of system checking...
- This is a freshly installed rebuilt M20B25 long block. Prior to removal of the old engine, the supporting accessories supported 8 solid hours of track time without a hitch. Doesn`t mean something hasn`t developed or gone goofy during re-install, just a note that I am not currently suspecting fuel pump or filter at the moment
- I have spark at all 6 plugs. Have not yet pulled them from my drive, have a mix of calls and waiting for the engine to cool completely before I start digging in
- All fuel injectors are firing. They are all fresh rebuilds as well. One bank does make considerable more noise than the other
- Fuel system is correctly hooked up
- Throttle cable is adjusted to spec
- CPS is brand new


I am thinking timing, but before I go through the pain of draining and refilling the cooling system again I was hoping to get some other expert opinions! Maybe a vacuum leak?

[gybe,]

Well, took the coolant system apart to check the timing and it’s dead nuts on, so, that’s great

Pulled the spark plugs; cylinder 2, 4, and 6 look normal after running while 1, 3, and 5 look fresh out of the box brand new...in other words, looks like I am running on 3 cylinders.

I have verified spark in all the cylinders and I redid the wiring in the loom for all the injectors (as well as pinned them out and checked for operation). When I verified operation for the injectors, I did note that the 2, 4, 6 bank were significantly louder than the 1,3, 5 bank. This seemed to follow the wiring (had spare injectors that were equally loud when checking operation on that side of the loom). Currently very stumped and appreciate any help!!!

[e30vert]

Doesn't the coolant sensor affect this? If the coolant sensor is malfunctioning then it tells the engine management to enter "limp mode" as it thinks the engine is overheated and should not be run in this condition?

[gybe,]

Yeah...I am currently at a total loss here. I am going to replace the three injectors in the suspect cylinders, but I can’t actually base that on any logical reason besides those being the suspect cylinders. As I said, I pinned these out on the main harness and each one was clearly working using that method, the only delta being that one bank of injectors (the current “ working” ones) could be heard clicking from inside the car while the other bank needed a stethoscope (screwdriver) to hear them open/close. While I have the harness out I will see if I can rig something up to check the current being supplied during operation

[gybe,]

I am completely stumped at this point, really appreciate any thoughts people may have on this one as I am at the point where I am just going t obe throwing money at it rather than really working to fix it.... Here are the additional things I have done, but I am running out of ideas at this point...
- With the ignition on, I checked the voltage on each rail for the injectors and they were matched (~11.5V).
- Checked impedance on all injectors to see if I had some weird mismatch, I don`t
- Checked for any odd shorts that I could be missing, haven`t found any
- Checked all fuses related to ignition and fuel delivery
- Cleaned and reseated all connections
- With the car running (on 3 cylinders), I went through and wiggled/shook the various connections without any change in the behavior of the car.
- Tried my old CPS (which was working fine at the time of the old engine removal), no change in behavior
- Kept the CPS loose and wiggled it with the car running to see if I could influence anything, no change in behavior
- Unplugged the ICV...Idle was certainly worse, but misfire was basically unchanged
- Reverified spark at all cylinders, still there

So, I have a car that runs on 3 cylinders. Appears that the 1, 3, and 5 injectors are not firing despite being able to trigger them from the harness and having continuity all the way through. Triggering the other bank of injectors (car not on) is louder. The DME (a 153 model) was working perfectly prior to pulling the old engine. Timing is spot on, CPS is brand new, and have verified spark on all cylinders. Completely stumped at this point, please help!

[mikey.antonakakis]

Check your valve clearance (just in case something slipped). Otherwise it almost certainly is the injector circuit - could have fried the output circuitry in th ECU?

[Andre3127]

E30 ECU's have two outputs for injectors. One for odd cylinders and one for even. Sounds like one of your outputs has been burned out or shorted.

Pin #16 controls these injectors.

[gybe,]

Yeah, I am thinking at this point it has to be either DME or wiring harness. Wish there was a way I could test the DME, as it just seems strange that it was working near perfect prior to pulling the old motor and the only touching of it was unplugging the harness. But, clearly something isn’t right and I am of the belief that it has to be related to the triggering from the timing...either the incoming signal from the CPS isn’t being interpreted correctly (harness) or the DME isn’t operating appropriately ( signaling).
I have verified and reverified that the injectors are connected through the harness, but the fact that the pin 17 bank (2,4,6) is so much louder still bugs me. Like it is telling me something that I haven’t grasped. There is not any additional resistance in the pin 17 vs 16 line (that is multimeter on pin 16 or 17 all the way through to the injectors harness output is matched), which is further supported by the voltage being equivalent when measured at the injector harness.

I am currently thinking of a way to wire a remote injector tied to pin 16 to see how it behaves when the car is running on 3 cylinders...where I can pull a spark plug and verify that it is firing, you can’t really do the same for the injectors. Add in the tractor like noise from the misfire and the Spec E30 exhaust, and its hard to hear anything with the stethoscope while it’s running. Currently just very frustrated and hate to just throw money at the problem wi5out really understanding what’s happening

[JehTehsus]

If you know somebody with a oscilloscope and have a few resistors kicking around you could try hitting the starter with the dme unplugged, see if you get a viable crank pulse on the end of the harness. That would at least verify the cps is working and spaced properly.

Otherwise, I am not sure what else it could be. Other than temperature what does the factory controller actually read? I know when I pulled mine apart there was a connection onto the plug number one wire, little CT clamp. I will skim over some photos later see if anything else stands out.

[mikey.antonakakis]

If you originally had a wiring/oxidation issue in the harness on one of the injectors banks, and the car seems like it's running on only one of the banks... Occam's razor and whatnot. It would be highly unlikely that it's the crank signal - that would likely affect all cylinders, not just one bank.
My money would be on the injector driver circuit in the ECU. The fact that the sound of the injectors on each bank is different is a pretty clear indication that one set of injectors isn't getting enough power. It probably won't tell you much, but try checking each injector output pin resistance to ground (on the ECU itself). They should be identical.
You could also use a multimeter in AC voltage mode (DC might work too) to check the voltage at each injector bank when cranking/running. Again, should be identical between the banks (even though the actual value won't mean much), and you can check at different spots in the harness to track down a wiring issue if you notice a difference between the banks. For example, if you notice a difference at the injector plugs, but not at the ECU pins, you've got a harness issue. A difference at the ECU narrows it down to an ECU issue.

[gybe,]

If you originally had a wiring/oxidation issue in the harness on one of the injectors banks, and the car seems like it's running on only one of the banks... Occam's razor and whatnot. It would be highly unlikely that it's the crank signal - that would likely affect all cylinders, not just one bank.
My money would be on the injector driver circuit in the ECU. The fact that the sound of the injectors on each bank is different is a pretty clear indication that one set of injectors isn't getting enough power. It probably won't tell you much, but try checking each injector output pin resistance to ground (on the ECU itself). They should be identical.
You could also use a multimeter in AC voltage mode (DC might work too) to check the voltage at each injector bank when cranking/running. Again, should be identical between the banks (even though the actual value won't mean much), and you can check at different spots in the harness to track down a wiring issue if you notice a difference between the banks. For example, if you notice a difference at the injector plugs, but not at the ECU pins, you've got a harness issue. A difference at the ECU narrows it down to an ECU issue.

I am there with you, especially the Occam's Razor ideal. Not certain about a way to check the voltage at the injector bank when running though? Could be missing something obvious there (or had too much to drink during this whole quarantine nonsense!), so sorry if that seems like a stupid question.
I have checked with ignition on and probing the leads at each of the injector mating points on the harness and they are all identical. Also checked the impedance of each of the injectors, also identical. I have the later style single rigid rail/harness, so just unplugging a single injector isn`t straight forward, hence my scheming to rig up an injector outside of the car. Good point on checking the DME's resistance to ground as well, something else I need to do. I think I can also check the current being sent to each injector bank by putting my multimeter between Pin 16/17 and ground on the harness, so that is something else I can check.

[mikey.antonakakis]

I have the later style single rigid rail/harness, so just unplugging a single injector isn`t straight forward, hence my scheming to rig up an injector outside of the car. Good point on checking the DME's resistance to ground as well, something else I need to do. I think I can also check the current being sent to each injector bank by putting my multimeter between Pin 16/17 and ground on the harness, so that is something else I can check.

Current check is a good idea I think! Just make sure you get the polarity right. Easiest way would probably be during cranking - unplug that intermediate connector for the injector harness (it just includes injectors and coolant sensor, right? Sorry I have an earlier model) and bridge across it - so whichever pin goes to one bank of injectors should be the "positive" lead, and the "negative" lead should go to the engine harness side, same pin (you need the current to flow through the multimeter).
You can use the same connection point for the voltage check too (I'd measure between 12V supply to the injectors and each of the DME output pins - the DME outputs switch to ground to fire the injectors, and have a low duty cycle at idle so in DC voltage mode the multimeter should read a relatively low voltage - a small difference between banks should be easier to pick up this way, e.g. 0.1V and 0.2V on each bank is an easier difference to notice than 12.0V and 12.1V).
Might also be a good idea to pull the fuel pump relay and ignition coil power for these checks. I don't think the fuel pump relay powers any of the injector circuit or anything on your car.

[gybe,]

Have a harness and a refurb DME incoming. Based on my latest round of testing I am thinking it is actually DME, not harness at this stage.

With the harness plugged in to the DME, ignition off, I am finding that pin 7 of the C191 (corresponding to injectors 2, 4, and 6, aka, the working set) has ~6-7ohms resistance to ground. Pin 6 (injectors 1, 3, 5) is basically shorted to ground (sub 1 ohm, inline with say pin 3 which is constant ground). Unplugging the harness from the DME I am finding both pins have over 100k ohm resistance to ground, and actually pin 6 is a bit higher. So, fingers are crossed that this thing will be running correctly once my replacements are in!

[mikey.antonakakis]

Keep us posted!

[gybe,]

Sadly, DME did not solve it and I have created a host of new issues with a new wiring harness. Posting a separate thread on that...

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m20/9921280-harness-swap-missing-pin-20-in-c101-bouncing-voltage-on-pins-18-37-and-27-in-dme