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2010 Thruxton head hurter: Firing on one cyclinder... injection pulse timing off. [SOLVED!!!]

2K views 4 replies 3 participants last post by  BlakeShaffer 
#1 · (Edited)
Hello all! I've got a real head hurter on my hands and hoping for some help or some thoughts on where to go from here.

I rode the bike to work the other day and it was just fine, hopped on to go home and it suddenly started running like crap; backfiring, stalling etc., but I was able to limp home.

The symptoms are EXACTLY what I found on this post (unfortunately no solution!): Correct resistance values for EFI ignition coil? ...
-Left cylinder not hot or firing
-Plug wet with fuel, injectors click properly with 12V applied
-Ignitor resistances reading properly
-Removed plugs from ignitor, resistances are the same and within tolerance

Additional info
-0 fault codes on Tune ECU
-Swapped Barometric MAP sensor with the #2 MAP to test it, issue persists.
-Injector pulse timings are wayyyy different (see two pics below)
What would cause this?
- Injector resistances reading properly
-Tried balancing the throttle bodies... this did not work and extreme adjustments made things worse with no appreciable MAP changes.
-Can't get the rev range below ~1200RPM with the carb adjustment knob
-Read the following posts (among many others):
1) Forchetto's MAP sensor dissertation: MAP sensors on EFI Bonneville- Long post
2) Grubscrew's Ignition coil grounding discovery: Engine Stutter Solved (Interesting Discovery)

I hooked up Tune ECU and the cylinder pressure from the MAP sensor on #1 (left side) is much lower than cylinder number 2 (right side). ~300/400hpa respectively.
I replaced both spark plugs with new ones, getting good spark on both plugs. I tested the ignitor coil in accordance with the Haynes manual (secondary winding was ~30kOhms vice 15 but other searches have revealed this is normal). All other readings were within tolerances.

The left cylinder/header is barely warm there is plenty of fuel on the plug.
I don't think it's a MAP sensor issue because the problem persists at higher rev ranges (determined later to be a false assumption!). Also, I'm not getting any MAP sensor or vacuum pipe codes and the pressures stay fairly constant when I move the piping around while running. (moving the tubing had no effect but ended up being the issue)

I swapped the plugs and the problem is similar but there are some odd/unexplainable differences in the MAP sensor voltage when I do this (see below).
There is something odd going on with the MAP sensor voltages below but I don't know what would cause this. Any thoughts? Ignition control unit?

I've read a ton of threads.... my next steps which I don't have confidence will fix the issue are:
1) Replace MAP sensor tubing when the tubing is delivered (again, I don't think this is it because there are symptoms at higher rev ranges and no codes)
Update, replaced the tubing going to the MAP sensors (couldn't get the manifold tubing off so I figured it wasn't leaking and left it...[update: figured wrong on this]). No change in MAP readings.
Final Update: replaced the tubing going to the manifold which seemed to solve the problem. While many posts suggest that the MAP sensors don't have any input after '6% throttle' and/or '2-3krpm', it seems they in fact do. Therefore, these symptoms seem to manifest at all power settings. At a minimum, symptoms at higher power settings should not be used to eliminate the MAP sensors!]

2) Compression check. Possible stuck valve? I'm waiting for the tool to be delivered.... not sure it would be such a drastic or sudden change though.
Update, did the compression check: 200 psi left cylinder, 190 right cylinder. Should be good here.
3) Check the crankshaft position sensor for infinite or no resistance as well as 'air gap'.
Update, 600 Ohms resistance, probably not the air gap due to sudden change, not pulling off the alternator cover just yet.
Wouldn't a failed/malfunctioning sensor give me a P0355 code? Would this cause a single cylinder issue?
4) Replace the ignition control unit.... not sure how this thing works. I've seen aftermarket replacements but haven't seen many posts on these failing.
Would this give a single-cylinder problem?
5) Replace ignitor? (seem to be on backorder everywhere :( and all the resistances check out)
Final Update: purchased a 'Nology' EFI coil and cables... wasn't the problem but new/better parts are always fun!
6) Replace injectors? (on backorder everywhere as well..., and the plug is soaked so fuel is getting in there.
Final Update: swapped the injectors but this was not the issue. (requires removal and disassembly of the throttle bodies, use caution here if you get this far)
Interested in some insight if anyone has it!


744720


Sensor readings:
744722


Swapped plugs from left to right:
744721


UPDATED Pics:

Replaced both 'connector' pieces of hose with 3mm Inner Diameter, 7mm Outer Diameter automotive hosing from Amazon. I also got those nice perfectly sized hose clamps in a box set from Amazon too. I did shorten each by about 4-5mm so the hard plastic was as close as possible to the brass manifold stub and the plastic stub on the MAP sensors. My thinking here was to minimize any effect the flex in the 'softer' hose would have on the readings. Forchetto has some good posts on this as well, where he also discusses the importance of cleaning off the manifold fittings. I used some carb cleaner to break down the hosing and glue stuck to the fittings.
745338


And from the right side:

745339


As you can see, the MAP 1 & 2 are nicely matched (especially after a bit of Throttle Balancing). Injector timing is lined up with the correct idle RPM and Throttle Position Sensor Voltage.

745337
 
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#2 ·
You have certainly done a considerable amount of trouble shooting.
It does not sound like an air leak issue as the one cylinder is not firing off the fuel.But I would do a air leak check everywhere to verify.
It does not sound like a fuel issue as you have fuel to the cylinders.
For the symptoms you described I would do the air leak checks then replace the ignition coil first and the position sensor after that. Easiest and most reasonable priced items which are known to have a failure rate over the years. I would bet it to be the coil breaking down.
One other thing to check that is simple - Both battery cables and connections to the battery. Also the ground lead for the electrical behind the engine. Not just connections made but clean and secure.
 
#4 ·
You have certainly done a considerable amount of trouble shooting.
It does not sound like an air leak issue as the one cylinder is not firing off the fuel.But I would do a air leak check everywhere to verify.
It does not sound like a fuel issue as you have fuel to the cylinders.
For the symptoms you described I would do the air leak checks then replace the ignition coil first and the position sensor after that. Easiest and most reasonable priced items which are known to have a failure rate over the years. I would bet it to be the coil breaking down.
One other thing to check that is simple - Both battery cables and connections to the battery. Also the ground lead for the electrical behind the engine. Not just connections made but clean and secure.
Back2-2,

Thank you for the reply. I did a bit more troubleshooting before hopping onto the forums today and low and behold, it was a vacuum leak as you suspected. I'll be adding some details to the original post (and the dead-end posts I found) so others can benefit from my troubles but I did two things: swapped injectors (to eliminate a faulty/clogged injector) and replaced the hoses near the manifold (I had originally only replaced the ones near the MAP sensors). Thank god it wasn't a grounding issue... I can imagine the frustration of chasing wires really getting on my nerves.
 
#3 ·
Your map readings indicate an unusually large difference between cylinders, and as you say that you've checked all vac connections and they are good. But even balancing the TB'S wasn't giving expected results my next step would be to check the linkage between TB'S, there is a little spring on the linkage that keeps tension on the adjusting screw, if this is missing then one TB butterfly is free to move a small amount independently to the other and cause the symptoms you describe.

I wonder if the bike could have been knocked over in your work place carpark thus dislodging this spring?......or maybe someone could have tampered with it?
 
#5 ·
Mike,

Thanks for the reply. As you can see in my reply to Back2-2 it was the other vac connection near the manifold. When I swapped injectors I was checking all those little springs and such as well.... the Haynes manual has been useful in the injector swap but there really needs to be more in there about the MAP sensors.
 
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