06 GTX 185 SC misfire?

[CJ1189]

I have a 2006 GTX 185 SC that I picked up for cheap because the supercharger let go. I rebuilt the motor to spec from the manual. Rebuild included rings, bearings, seals, gaskets, supercharger, both oil pumps, valves cleaned and lapped, valve seals, impeller and wear ring. Upon first start up I noticed it sounded like it was only running on 2 cyl. So far my diagnostics have consisted of:
1) I pulled the coils one by one as the engine was running. There was no change in engine performance when I pulled coil #2. There was a change in performance on coils 1 and 3. To confirm this i swapped the coils around and the problem still stayed on cylinder #2. My conclusion would be that the coil packs are good. I checked resistance in both windings and they all checked out.

2) I checked for 12v coming from MPEM on each connector for each coil. All were good with 12v.

3) I checked for voltage on the ECU switched ground side of each connector for each coil. I got around 1v or less on each one. Should there be any voltage on these wires since they are supposed to be switched grounds? Seems like there should be no voltage at all there.

4) checked for continuity and resistance in harness from "A" connector on ECU to each coil connector ground side. All had continuity and all have .6 ohms resistance. Should there be any resistance on these wires?

5) checked and cleaned all ground connections on the block and battery.

**I should add that codes for the crank sensor and the cam sensor have activated randomly but if I turn the ski off and wait a few seconds the codes go away and the ski starts up fine. The ski will intermittently smooth out like its running on all cylinders but only for a few seconds and then back to misfiring. I am starting to run out of ideas on what it could be. Any help or info would be GREATLY appreciated. Thanks in advance and happy safe riding!

 

[ski-d00]

I assume you have new spark plugs and you've switched them around to confirm it is a cylinder 2 problem as I've seen new plugs bad out of the box.
Have you checked for spark on cyl 2 by removing plug and grounding while running? It may be a fuel injector issue and not a spark issue. Easy to remove fuel rail and watch spray pattern while cranking.

What you describe is typical of ECU failure where it loses spark to one cyl. Did anyone jump start the ski?

 

[mkov608]

3) I checked for voltage on the ECU switched ground side of each connector for each coil. I got around 1v or less on each one. Should there be any voltage on these wires since they are supposed to be switched grounds? Seems like there should be no voltage at all there.

Did you do this check with the connector connected to the coil? You won't have any voltage on the ground side because 100% of the voltage drops through the load in the circuit; the voltage (from your step 2) comes from the MPEM; if you have a BUDS or CanDoo Pro, you can connect an LED (LED only!!!) test light to battery positive, and the tip of the test light to the ground side of the injector connector (disconnected); then activate the injector with BUDS/CanDoo and see if the test light illuminates. If the test light illuminates, the driver circuit in the ECU is good; if not; it's bad. This will not hurt the ECU if you use an LED test light because the LED test light is about 2mA current draw. This will confirm if the ECU driver circuit is working. You can do this same test on the ignition coil circuits too as both the coils and injectors are ground-side switched circuits.

4) checked for continuity and resistance in harness from "A" connector on ECU to each coil connector ground side. All had continuity and all have .6 ohms resistance. Should there be any resistance on these wires?

Yes, but it should be very low ... < 1 ohm; make sure you zero out your meter.

5) checked and cleaned all ground connections on the block and battery.

**I should add that codes for the crank sensor and the cam sensor have activated randomly but if I turn the ski off and wait a few seconds the codes go away and the ski starts up fine. The ski will intermittently smooth out like its running on all cylinders but only for a few seconds and then back to misfiring. I am starting to run out of ideas on what it could be. Any help or info would be GREATLY appreciated. Thanks in advance and happy safe riding!

I just repaired a ski that had the same "misfire" type fault, but no misfire DTC was stored in memory; however, I did have a crankshaft DTC; I put a lab scope on the crankshaft sensor, and I could see the signal was dropping out; I replaced the crankshaft sensor, and the ski was back to normal.

Check out this post: Wave Form Library

The ski was running like it had a misfire.

 

[Coolride17]

I change injectors all the time on cars that are causing a cylinder miss in one cylinder.

 

[CJ1189]

Hi guys, thanks for all of your useful input! I had originally tested the stock oem injectors by removing the fuel rail and cranking the engine over and watching the spray patterns (very dangerous i know, I had coils diconnected). The spray looked fine to me but I decided to go ahead and pull the injectors out of the rail and they were completely full of nasty crud. I replaced them with Bosch injectors and that completely fixed the problem! The ski is running like a champion and firing on all cylinders now. I should have started with the simple things like plugs and injectors. Lol. Again thanks for the quick and helpful responses! Happy and safe riding

 

[mkov608]

Excellent, but how did the spray pattern look fine while the injectors were "full of nasty crud"? Did the spray pattern look different with the new injectors, or did you simply install them and fire it up?

You might want to check your fuel tank before you plug up the new injectors; that crud had to come from somewhere.

 

[Coolride17]

Excellent, but how did the spray pattern look fine while the injectors were "full of nasty crud"? Did the spray pattern look different with the new injectors, or did you simply install them and fire it up?

You might want to check your fuel tank before you plug up the new injectors; that crud had to come from somewhere.

That's good advice.

 

[acooper]

As a lifelong mechanic, I really admire the knowledgeable individuals that come forward on this Forum. When S.F.I. was fairly new to the U S automotive industry, we could pull injectors and send them out to be bench tested. Obviously, it would be a huge waste of time NOW because the price of injectors is much lower and the availability is so much better..
It would be interesting to see if "Ethanol crust and dust" has claimed another victim in this case, right?
I totally agree with "You might want to check your fuel tank ...."

 

[CJ1189]

Excellent, but how did the spray pattern look fine while the injectors were "full of nasty crud"? Did the spray pattern look different with the new injectors, or did you simply install them and fire it up?

You might want to check your fuel tank before you plug up the new injectors; that crud had to come from somewhere.

Well this is my first 4-tech engine and when I observed the spray it looked to be sufficient but my guess was there was supposed to be alot more fuel spraying out than what was, even though the patterns appeared to be even. And yes I purchased the candoo diagnostic system and tested the new injectors properly that way lol. There was definitely more fuel being injected with the new injectors and I can actually hear them clicking while the engine is running while the old ones I could not hear. Thanks again everybody.