a10beav

A friend over here is having fuel consumption problems in his Firehawk after storing it for several months, the car was not started at all during storage. He says the fuel consumtion has worsened almost 50% and he hasn't changed anything since parking it. It seems odd to me and I couldn't think of a reason for it.

He said he pulled an O2 sensor and a spark plug and they're both black, there is no check engine light either. The MAF was previously removed and it's running on air density.

Any reason the fuel gauge might be wrong now? I'm not sure if he added a fuel stabilizer before parking it, but I don't think that would cause a problem like this.

Any ideas?

slayerized6

iTrader: (12)

see what happens on his next fill up. the gas could of gone bad without stablizer

Garry

I filled up from ~1/3 tank before the last trip ...

OK, here's a couple more details on the matter ...

I pulled the drivere side O2, and it looks "normal", no residue, at least nothing like on the passenger side ...
I also took out one of the driver side spark plugs, it's in perfect condition ... if the car had general problems with the fuel, I doubt it would only manifest on some of the plugs and not on others ... also, the black plug had fuel on the treads, which for me really points towards it not firing at all or enough ...

I check the gapping of the two plugs, both are identical at about 1.5mm

I've now swapped the two, and will need to run the car a couple miles and see if the problem is still on the passenger side ... I guess I will also need to re-check the cables going to the coil and from the coil to the spark plug ... didn't have my volt meter with me to check for resistance on the spark plug wire ...

Anybody happen to have a suggestion as to where to start further "debugging"?

(Please note, the car was running fine last October, I'm running a custom OS from EFIlive, with Speed-Density tune Open Loop. Tune is still the same, and it has been close to perfect AFR BEN with mostly +-1% variation.)

Tnx, -garry

a10beav

Maybe it's just time for a tune-up. When's the last time you changed the plugs and wires?

MEM

check: fuel-air ratios and ignition system (plugs,wires,coil)

vettenuts

iTrader: (4)

Where was the car stored? Check for chewed wires from mice. Do you know if the bank is getting spark? Doubtful something mechanical has gone wrong, but mice will wreak havoc (or other critters).

Garry

Plugs were new during the rebuild ... (that is, Apr 08, ~2500mi since then)
Wires - possibly / probably still the stock ones ...

AFR was perfect when I stored it for the winter ... still the same tune in the PCM ... plus, wrong AFR wouldn't just affect one bank but not the other ... my money is on something ignition-related ...

At least the plug wire in question (passenger side rear) that has the fouled up spark plug looked fine, haven't checked every cable under the hood, but didn't see any obvious chewed-up cables ... haven't heard from any of the other folks there that they'd ever had problems with critters ... (got about 6 cars in total there, plus a varying number of cars that are being worked on ...)

Oh well, set a date for Friday to go to the mechanic that did the rebuild ... see if he can manage to pull the other three PS plugs ... see if any of those are messed up, also, or if it's just one ... hopefully it's just a minor problem ...

crainholio

iTrader: (2)

Mine had a noticeably lazy throttle when I fired it up last month, so I hooked up the scanner. Didn't notice anything at first, but the LTFT table (gotta love EFILive) showed my fuel trims were off by over 5% across the board on the passenger bank.

The PCM was adding fuel on the pass bank, so possibly a stuck/clogged injector there.

I swapped in a set of new injectors I had on the shelf, cleared the PCM, and problem was solved. Throttle was nice and crisp again, and after ~100 miles of mixed driving the LTFTs were back to within ~1% between both banks.

I may send the old injectors off for a flow 'n clean treatment, if so I'll post the results.

Garry

Hm ... with me running OLSD, the LTFT shouldn't be a problem, or?

Also, I pulled the plug wire off of the PS spark plug last night - got something around 800-1000 ohms of resistance when I measured ... not sure if that is normal ... I saw different aftermarket plug wire replacements that advertise something in the area of 40-50 ohms per foot length ... (though, at other place I found references stating up to 20ohms per millimeter or 10-15kohms for spark wires that are "good" when comparing to a defective one). I'm confused ...

vettenuts

iTrader: (4)

That wire is fine. Have you checked fuses, etc.

crainholio

iTrader: (2)

I only pointed out LTFTs on mine because that showed an injector problem.

The LTFT wasn't the problem, it was an indicator of the problem which was one or more injectors on that cylinder bank.

Yours may be an injector problem as well.

Garry

well, can't get anything out of my LTFT, they're 0 from beginning to end ...
Guess one of the first things to do is pull more of the PS plugs and see if they're also messed up ...

Garry

Well, turns out that the cause and effect is somewhat reversed ... I had thought my OLSD tune had disabled the O2 input for the PCM, but it didn't ... with the WBO2 shot, the PCM kept thinking the PS cylinders were running lean, causing it to dump additional fuel into it ... threw out the WBO2 and put the old NBO2 back in, apart from the LTFT adding slightly more fuel at the moment, both sides are near synchronous ...

crainholio

iTrader: (2)

That doesn't make sense given your early data of 0 LTFTs across the board, LTFT is how the PCM adds fuel. But congrats anyway, glad to hear it's fixed.

Garry

Since when do computers make sense? Seriously, I have no idea why I got the readouts I got ... especially as the WBO2 had no problems identifying free air, and when firing up started out at 14.x, only gradually rising ... oh well ... main thing is it's fixed for now ... will get a new sensor some time and put it back in ...