I had my plugs and wires changed and now my gas mileage sucks.

[CommandD]

I usually get 13 mpg in the city, but my engine started to misfire and my mpg dropped down to 10mpg.

I took it to the shop and they said I needed new plugs and wires so I had them install a set. I also had them install a new fuel filter.

The engine sounds fine, but now my mileage has dropped down to 6mpg.

Plus, their is a gasoline smell coming that seems to be coming from the engine compartment.

Is it possible they put them in wrong? Since it was getting poor mileage before there must be something they missed. What might it be?

 

[celly]

Throwing any codes? I had an elusive vacuum leak for several months and my mileage went down to around 12 mpg from around 15-16 mpg. Was running pretty rich before I finally solved the problem.

Which engine do you have?

I had a P1151 code with my 5.0 and it's been a month since I solved it and mileage has been great, even with winter gas (not that you have to worry about that in LA).

 

[CommandD]

I have a 2WD 1997 FE Limited with a V8.

I don't know how to get the codes.

 

[celly]

I have a 2WD 1997 FE Limited with a V8.

I don't know how to get the codes.

Does your "Check Engine Light" come on? Mine did often on my V8. It had a gassy smell too. My leak was either a result of the PCV not being seated properly or the breather tube that comes out of the oil filler. I tried everything to solve including new plugs and replaced several wires that got torched slightly by my headers. Took me about 4 months to solve my issue.

I have several methods of reading codes, including my Scangauge, my SCT XC2 flasher and a cheaper Actron reader.

It's nice to be able to read your own codes. I understand some parts places in the US do it for free. No such luxury in Canada that I know of.

 

[celly]

p.s. if you get a P1151 code like I had, these are the things to look for (I copied this list from another site)

Electrical:
Short to VPWR in the harness or HO2S
Water in the harness connector
Open/shorted HO2S circuit
Corrosion or poor mating terminals and wiring
Damaged HO2S
Damaged PCM
Fuel System:
Excessive fuel pressure
Leaking/contaminated fuel injectors
Leaking fuel pressure regulator
Low fuel pressure or running out of fuel
Vapor recovery system
Induction System:
Air leaks after the MAF
Vacuum Leaks
PCV system:
Improperly seated engine oil dipstick
EGR System:
Leaking gasket
Stuck EGR valve
Leaking diaphragm or EVR
Base Engine:
Oil overfill
Cam Timing
Cylinder compression
Exhaust leaks before or near the HO2S(s)
Possible SolutionsSee the above list of causes and go from there.

 

[CommandD]

Great list - thanks a lot!

No, my check engine light is not on, but it didn't come on when the engine was misfiring either.

 

[celly]

Great list - thanks a lot!

No, my check engine light is not on, but it didn't come on when the engine was misfiring either.

I never got a CEL when I've had plug related misfires either. Same held true with a nagging gasket leak on my headers too.

Vacuum leaks can be a pain to find. I bet that might be your problem.

 

[shooked]

Follow the wires from the coils to the plugs, make sure its wired correctly. I once wired by BBC backwards, it ran fine, no missing or anything, but it didnt have near the lope at idle it should've. Make sure non of the wires are crossed, if they are crossing each other make sure they are at a 90 degree angle. Also, check to see if any of the wires are burnt.

good luck bra
shooked <///><

 

[SoNic67]

"New" wires can be at fault due to defective crimping, bad resistive "wiring" (that is made with nylon impregnated with carbon). It happens often with cheap brands.
Measured they should have some 10...15 kohms per foot.

 

[Richfla]

If you had a shop do the work, you should ask them. At least have them explain exactly what they did.

And have you looked at the fuel filter that they put in? Maybe there's a little leak...from everything you described, that's what it sounds like to me. Make sure they didn't put it in backwards.

 

[CommandD]

So I just picked up my car from the shop after I insisted they check the spark plugs and fuel filter they just installed that caused my current problem. They said they found no other problems which would cause the gas milage to drop by half. They suggested that I replace two of the oxygen sensors as "that might help." For $700 bucks!!!

Unbelievably, again, it is worse than it was when I dropped it off last night!

Now the MPG has dropped to 5 mpg and the misfire is back.

My new question is whether the car is safe to drive with it its high rate of fuel burn?

What damage might this cruddy mileage be doing to other parts of my engine?

 

[Cranmaro99]

So I just picked up my car from the shop after I insisted they check the spark plugs and fuel filter they just installed that caused my current problem. They said they found no other problems which would cause the gas milage to drop by half. They suggested that I replace two of the oxygen sensors as "that might help." For $700 bucks!!!

Unbelievably, again, it is worse than it was when I dropped it off last night!

Now the MPG has dropped to 5 mpg and the misfire is back.

My new question is whether the car is safe to drive with it its high rate of fuel burn?

What damage might this cruddy mileage be doing to other parts of my engine?

Damn. 5mpg means you need to go to another shop so they can diagnose correctly and from a fresh start, as these other guys are going to just clearly replace parts for money until if/when they actually fix the issue.

 

[CommandD]

Also, the mechanic (I now use that term loosely) said there were codes when I talked to him on the phone, butt when I picked up the car he changed his story and said there were no codes.

 

[SoNic67]

Dumping in exhaust too much unburned fuel can melt your catalytic converters.

 

[Richfla]

The last thing I'd do would be to ask them to put in 02 sensors. That doesn't sound like the problem, and they sound like they are just guessing at this stuff anyway.
Did they say any of the plugs looked fouled when they took them out? That info would be helpful.
You might want to check the distributor cap, but that's a guess as much as anything. The only reason I'd go back to them is to let them look for the codes again (while you're there), but I wouldn't give them another nickel.