Idle miss when hot / bad fuel consumption. 10 months on......

Cam · 19-07-2013, 09:09 PM

Ok, so as many of you know I am traveling OZ in my AU. I've now been chasing this issue for 10 months and am at my wits end.. Sorry for the long post, just wanna give as much info as possible, as I rely on my car very heavily.. Car is a AUII fairmont wagon.

Description: as the car gets warmer it gets a very pronounced "miss" at idle. Once the miss starts the car seems to loose power and fuel usage skyrockets. The miss is NOT consistent so it can be like brrrrrrrrrrdbrrrdddbrrrdbrrrrdddbrrrrrr at idle (I hope y'all making that noise in your head). I can be sitting at some lights and The the car is fine, next set of lights it goes bad. And visa versa.

I recently did a trip (without my van) from Brissy to Newcastle (admittedly I have a roof cage, and had 200kg of stuff in the back) and all highway driving (and driving nicely) I ended up with 13.6l/100. I never ventured more then 2km from the highway the entire time. When I first hit the road my consumption (based on the fairymonts l/100k calculations) will sit happily in the 9.0-10.9l/100 range, after a couple of hours of driving it's ramping into the teens..

I HAVE noticed that under light load the instant l/100 often goes (example) 10,12, 10, 11, 38, 42, 10, 11 and so on.

So far, I have changed... (last 8000km) plugs, leads, coil, fuel filter. Last 3500km - 02 sensor (now done twice), intake manifold gasket, CHT sensor, battery terminals. Last 2500km- tps*, iat*, map sensor,* (* = second hand) fuel pump, replaced collapsed rear muffler, second 02 sensor, cleaned TB and isc again, Pcv (now twice, just ditched metal one for a genuine ford one), compression test (185-188 all round dry test). Most recently I've had the car checked for fault codes, there was a fault for the tps that he cleared, and then confirmed it was operating as expected. He did mention the 02 sensor seemed slow to respond, but obviously was unlikely to be the cause of my issues. We also found the CHT voltages were way below what they should be, around the .4v despite it showing operating temperatures of around 88deg in his workshop. It's also worth mentioning I do seem to have some pretty serious blowby, thus why I swapped pcv for a genuine ford one.

He feels that because of the symptoms I have done a headgasket (between 5/6, despite no coolant loss / contamination). Or the CHT sensor is faulty.

So, I'm left with... Faulty ECU (read stories of ecus killing coils), leaky / blocked injector or fuel rail, fuel reg going AWOL, crank angle sensor, the second hand iat, tps or map sensor were rooted (seems unlikely I'd have the same issue, all tested ok), some kind of failure (bent rod, sticky valve etc), bad earth (adding another earth point just in case, seems unlikely IMO), or a blown head gasket.

The issue I mentioned earlier with the instant l/100 going off the scale makes me think it's electrical. It takes a lot of throttle at 100km/h to get it to read upwards of 40l/100, so I'm 100% sure it's not me slightly moving my foot..

I feel like burning this thing and buying a BFII wagon, so for eff sake someone help me before I do it!

/end rant
Cheers,
Cam

**auIILTD** · 20-07-2013, 10:52 AM

Cam, the instant L/100 thing happens on my car as well. Just never thought much about it. I am pretty sure that it is not another symptom of your bad fuel economy.

Good luck with it.

Stu

**Whoosha** · 20-07-2013, 08:26 PM

Pull the fuel pump and check the sock for gunk build up and get the pressure checked

Evgeni · 23-07-2013, 06:31 PM

Hi mate,
Probably a good time to invest in an elm connector and download forscan to get an overall picture of what is going on. I got mine for under $20, so it is well worth it when you are trying to solve an issue such as this.
Good thing is you have replaced a lot of the sensors so you can rely on
the data you will be getting.

In relation to the coolant temp sensor I was discussing this a while ago with another forum member and the voltage at operating temp was around 3.8v or something like that. I was expecting it to be lower, but checked on my car and it seems to be the norm.

Do you know what the code was? Maybe nothing, but check that you have a constant 5v feed at the tps, and a ground that is under 100mv. You want these to remain stable whilst snapping the throttle a number of times. This at least will get the spotlight off the computer.

The computer switches each coil on and off by giving the coils ground. If you are suspecting anything, perhaps have a look at what is feeding it - alternator output, and crank signal. By unplugging the sensor you will see 5v from one of the wires and nothing on the other. The wire with nothing is the one that will trigger the coils. It is a/c voltage - you want to see something that doesn't fluctuate at idle. Note that it does increase in frequency and magnitude at higher rpm.

Does pinching off the return line on the fuel rail change anything at idle?
Misses at idle usually point to a vac leak - you can track it down using o2 sensor readings and fuel trims. Sometimes spraying carb clean wont pick it up.

Anyway, just some thoughts to get some direction.

**auIILTD** · 23-07-2013, 07:29 PM

Quote:

Originally Posted by Evgeni

Hi mate,
Probably a good time to invest in an elm connector and download forscan to get an overall picture of what is going on. I got mine for under $20, so it is well worth it when you are trying to solve an issue such as this.
Good thing is you have replaced a lot of the sensors so you can rely on
the data you will be getting.

In relation to the coolant temp sensor I was discussing this a while ago with another forum member and the voltage at operating temp was around 3.8v or something like that. I was expecting it to be lower, but checked on my car and it seems to be the norm.

Do you know what the code was? Maybe nothing, but check that you have a constant 5v feed at the tps, and a ground that is under 100mv. You want these to remain stable whilst snapping the throttle a number of times. This at least will get the spotlight off the computer.

The computer switches each coil on and off by giving the coils ground. If you are suspecting anything, perhaps have a look at what is feeding it - alternator output, and crank signal. By unplugging the sensor you will see 5v from one of the wires and nothing on the other. The wire with nothing is the one that will trigger the coils. It is a/c voltage - you want to see something that doesn't fluctuate at idle. Note that it does increase in frequency and magnitude at higher rpm.

Does pinching off the return line on the fuel rail change anything at idle?
Misses at idle usually point to a vac leak - you can track it down using o2 sensor readings and fuel trims. Sometimes spraying carb clean wont pick it up.

Anyway, just some thoughts to get some direction.

Great post and great information Evgeni.

Stu

Cam · 24-07-2013, 02:37 PM

Thanks for the posts guys, looks like the verdict is in...

After posting this I did a 250km drive. Got to my destination to find water and condensation literally spewing out the exhaust. After our trip to the zoo and a run into town turned the car off and I literally had a constant drip of water from a hole in my exhaust. Car is becoming more and more gutless by the day.. When i popped the lid on the overflow the other day whilst the car was hot there was a constant stream of air beig pushed into the overflow. So it's looking like the head gasket is in fact gone. I've had some issues With what seems to be stupid amounts of oil through the pcv, so guessing its further confirming my suspicions. I'm only losing the slightest bit of coolant (for now) but its now starting to become noticeable, and the idle issue and gutlessness is definately getting worse. I now can't get better then 13.3/100 @100k on flat roads, regardless of how hot the car is..

Having a hard time convincing myself to fix it over buying a BF or a Terri..

**auIILTD** · 24-07-2013, 03:38 PM

That's bad news Cam. At least you know what it is. Shame too though, as I know you have a nice new tranny!

Cheers
Stu

Evgeni · 24-07-2013, 04:13 PM

Damn - one of the rare AU gasket failures.
If your travels take you to Syd, you have access to a garage, air tools and a cuppa for an engine removal if you need it.

Cam · 27-07-2013, 02:29 PM

Quote:

Originally Posted by auIILTD

That's bad news Cam. At least you know what it is. Shame too though, as I know you have a nice new tranny!

Cheers
Stu

Certainly far from ideal! It's not an easy decision deciding if I am going to part with it. With gearbox, brakes, suspension work all being done in the past 2000km it's a hard task taking 1500-2k from a car yard!

I've run into a few dramas with my plans to upgrade to JCs old Terri, so if things go south I might not have a choice but to pay someone to do the head gasket. I'm so over working on this thing that the labour costs would be cheaper then a few sessions with a psychologist....

Cam · 27-07-2013, 02:32 PM

Quote:

Originally Posted by Evgeni

Damn - one of the rare AU gasket failures.
If your travels take you to Syd, you have access to a garage, air tools and a cuppa for an engine removal if you need it.

Thanks heaps for the offer mate, after an engine swap, a couple of gearboxes, brakes, suspension, a host of sensors etc etc all in 7 months I'm so over working on this thing it's not funny!

JC · 29-07-2013, 09:35 PM

So this is the thread you were talking about - what a drama!

Terri is here waiting........

Cam · 30-07-2013, 04:13 PM

Deal has been done, I leave to pick up JCs Terri tomorrow morning.
I do have my AU to flog off at a dealer. But if someone on AFF wanted it for the same amount of money as I can get throu a dealer it's gotta go tomorrow. Has a 1000km old reco box (20000km warranty). Car has 190k, new pump, extra leaf and raised 1", 2000km old slotted rotors all round, all of the above sensors etc all replaced as well. Just needs the headgasket done and it'll be good for another few years at least! No mixing of oil and coolant, so the engine itself is fine...oh, and it's a AUII fairmont wagon...