d2mcgill

Hello all,

I’m a senior mechanical engineer, with 7 years in Formula 1 (McLaren and Caterham) and over 20 years restoring and rebuilding classic cars, I thought I’d seen it all, but I’m utterly stumped with this HHR, and desperately need some community help. I have a 2009 manual trans (5spd) HHR with the 2.2 litre engine. The car only has 65,000kms (40,000 miles) yet it’s developed a fairly significant misfire.

Misfire occurs predominantly under load in the 1300 to 2200 RPM range, but it’s intermittent, misfire occurs 90% of the time, but on rare occasion the engine runs without fault. Environmental factors (heat, cold, moisture level etc.) seem to have no effect or relevance to the fault.

-no codes (nothing stored, no CEL)
-no vacuum leaks
-fuel pressure and flow ok
-injectors good
-live data (fuel trims, lambda data, MAF all seem to be within tolerance)
-cylinder compression ok
-spark plugs replaced (symptoms remained unchanged)
-coil pack resistance appears to be within specification
-borescope shows clean valves, no significant carbon build up.
-all grounds checked, including to the ECM.
-gas is fresh and clean
-head gasket good

I’m tempted to just replace the ignition coil packs, but they check ok when I measure the resistance, I get no fault codes, not even any stored codes, which is very strange if it was a failing coil.

Has anyone out there had a misfire under load between 1300-2200 rpm with or without codes? Or does anyone have any theories what could cause such a fault without flagging any type of error codes?

Are coil packs a weak point or known to fail regularly on these cars?

Thank you in advance community.

RJ_RS_SS_350

to the forums!

You should be using the ACDelco 41-103 spark plugs, others could cause problems.

Have you cleaned the throttle body?

d2mcgill

Hello,

Thank you for the reply, I really appreciate it. Yes I am using new OEM AC Delco plugs. Throttle body is clean.

Do you know what the coil pack resistance tolerance should be? Or where I could find this info? (Google gives conflicting figures).

Dave

Oldblue

Dave, welcome to the site, check for loose ground wire and how about the timing chain, the front guide might be starting to break up, or chain stretching.

donbrew

I don't know how there could be a misfire without a P010x code. Maybe, loss of power would be a better description?
Fuel pressure and flow is ok? What does that mean?
Is coolant disappearing?
What is compression?

My first guess would be a fuel pump.

geg

I would also think about the chain first. But it's too early for the timing chain. Total 65,000 km of run (if the run is not twisted).
The goblin is hiding somewhere in the electrical grid. I'm afraid that I will have to consistently change components starting with the spark plugs.
By the way, how about an oil leak? Is there oil in candle wells?
Have you checked the operation of the injectors? Improper operation of one of the injectors can flood the spark plug.


PS. If you do not find the reason ...
You may need to reflash or replace the onboard brain. I have not come across this in reality, but I heard that GM computers sometimes buggy. It seems that the center tire on some cars is subject to corrosion.
And grounding, as Oldblue said ... Be sure to check.

RJ_RS_SS_350

I don't know what the spec is for the coil packs. You didn't completely answer either of my questions, both answers were generic.

d2mcgill

Thank you everyone for the tips and pointers. It feels like a very distinct and clear misfire and my understanding of US emissions laws is that since the late 90’s all cars must create a fault code whenever there is a misfire, even if it doesn’t trigger the CEL, so I should be at least seeing a P0300 code... right? However, I have absolutely no codes, yet my car lurches and coughs under load at low RPM, especially going uphill, but as soon as I’m above 2300rpm all the way up to the redline, the car runs clean and smooth... It’s baffling.

Compression and leak down tests were both very good, (compression above 177psi on all cylinders), fuel pump pressure is about 65psi. I removed the fuel-rail and ran the injectors into plastic measuring cups and they are all firing a nice mist at near identical flow rates. Timing chain has no slack and the runners and guides have virtually no wear judging from what I can see with a borescope. I don’t know exactly what the resistance on the coils should be, but all 4 give very similar ohms resistance (10.2-10.3 at 2k), so I suspect they are NOT the issue. I’ve tried different fuel grades from 87 to 91 octane and E85 (resetting ECU between fill-ups), yet the misfire remains consistent. No coolant leaks, no oil leaks, no aftermarket parts ever used, only genuine GM, no mods (other than LED headlight bulbs), battery holding 13.4 volts resting, alternator generating a consistent 14.2 volts above 1000rpm and control module grounds seem strong, (even tested adding an additional ground to the ECU casting last month).

I’m lost, so I’m going back to square one and replacing the plugs again today.

d2mcgill

Sorry, didn’t mean to give a generic answer, the plugs came from the dealership and had the same part number as the ones being removed. That said, I did not specifically note if they were the ‘41-103’, but I did quickly cross reference them to the ones I was removing and the part numbers matched what came out, but I will double check now as I’m about to pick up another new set today.

Throttle body was virtually spotless, but even so, I removed it and wiped it down with brake cleaner when this issue first started last month.

Oldblue

First , I suggest cleaning and inspecting ground wires, and re clean the throttle body with the correct TB cleaner, then clean the MAF sensor, with proper MAF sensor safe spray cleaner. And is the connections at all the coils and the MAF sensor, clean and tight a little dielectric grease helps a lot!

how exactly did you see the timing chain with a borascope, and that brake cleaner on the throttle body could cause the butterfly blade to stick just a bit.