[yzrider250]

Hey guys, I have a 1998 gt with a 2004 gt motor, 98 transmission, o/r h pipe, flowmaster exhaust, bbk fenderwell intake, accufab 70 mm plenum and throttle body, MSD coil packs, 4.10 gears, Steeda*under drive*pulleys, aluminum*drive shaft.
My check engine light is on with codes ("p0136" p0136 02 Circuit (bank 1, sensor 2)(see p2270, p2271))and ("p0141" p0141 02 heater circuit (bank 1, sensor 2)). I get 10 miles to the gallon and the performance isn't great and I tried to install wire in mil eliminators, but i'm not sure if they are working because they didn't make any difference when I installed them. The car has 140000 miles and the motor supposedly had 40000 according to the owner, around 2k miles ago I changed the motor and transmission oil, did new spark plugs and wires, new oil and fuel filter, replaced the IAC valve, replaced the intake manifold with a new stock one and put in a new thermostat. replaced one injector because it was broken(it's a different color than the other ones but Levine's said it was the same pressure, but it might not be?), put in the msd coil packs(the wiring harness is from the 98 not the 04, so it has plug wires not coil on plugs), the maf sensor seemed clean when I had it all apart. My rear end is whining really bad and all the bearings are shot in it. I don't know if it puts a lot of drag on the motor and kills my mileage? I'm getting it done tomorrow with 3.73 gears so it should be fine. I've tried what seems to be everything to get my gas mileage to be good, but it still sucks. Does anyone have any ideas that I could try? It can't be normal to get 10-12 mpg with normal driving

[Macattac]

Originally Posted by yzrider250 Hey guys, I have a 1998 gt with a 2004 gt motor, 98 transmission, o/r h pipe, flowmaster exhaust, bbk fenderwell intake, accufab 70 mm plenum and throttle body, MSD coil packs, 4.10 gears, Steeda*under drive*pulleys, aluminum*drive shaft. My check engine light is on with codes ("p0136" p0136 02 Circuit (bank 1, sensor 2)(see p2270, p2271))and ("p0141" p0141 02 heater circuit (bank 1, sensor 2)). I get 10 miles to the gallon and the performance isn't great and I tried to install wire in mil eliminators, but i'm not sure if they are working because they didn't make any difference when I installed them. The car has 140000 miles and the motor supposedly had 40000 according to the owner, around 2k miles ago I changed the motor and transmission oil, did new spark plugs and wires, new oil and fuel filter, replaced the IAC valve, replaced the intake manifold with a new stock one and put in a new thermostat. replaced one injector because it was broken(it's a different color than the other ones but Levine's said it was the same pressure, but it might not be?), put in the msd coil packs(the wiring harness is from the 98 not the 04, so it has plug wires not coil on plugs), the maf sensor seemed clean when I had it all apart. My rear end is whining really bad and all the bearings are shot in it. I don't know if it puts a lot of drag on the motor and kills my mileage? I'm getting it done tomorrow with 3.73 gears so it should be fine. I've tried what seems to be everything to get my gas mileage to be good, but it still sucks. Does anyone have any ideas that I could try? It can't be normal to get 10-12 mpg with normal driving

Have you checked your cats and o2 sensors? How many miles on the MSD coils? Do not know, but they might be shot, and as far as I've gathered the OEM's - though expensive - are far superior as far as quality goes...

Hope some of the guru guys/girls here can solve your issues!

[jeep45238]

Both downstream sensors are showing bad, and the car seems sluggish? I'd check out the cats themselves, they may be clogged.

Fix everything first, and then start to figure out economy - they are probably very closely related.

[04MidnightGT]

Rear O2's don't have anything to do with performance, OP how does the motor feel? Strong or sluggish, hickups, sputtering?

[WickedSnake00]

MIL's won't make any difference other than cause your CEL for P0420 to go away if you're running an O/R midpipe, ie you're catless.
It also sounds like they may be installed improperly or are defective if they're throwing a heater code for the downstreams.

Pull your MIL's out and clear codes. See if the heater codes come back. If they do, it's not the MIL eliminators, it's probably the sensors.

Also if the cats were plugged they should throw a catalyst inefficiency code, P0420 IIRC.

That would be the first thing I'd do.

EDIT: New HOS's wouldn't hurt either. Do they look OEM? The PO may not have changed them, and if it's up to 140k mi, I can easily see them being bad.

[yzrider250]

There can't be more than 1,500 miles on the MSD coils, the front O2 sensors can't have more than a few hundred miles, the rear O2's are old but I have a cat less exhaust so it shouldn't effect it with the mil eliminators. The HOS are Bosch, because I could get them cheap, but I just changed them to see if that would help my mileage and it didn't do anything. The code existed before I got the eliminators. I bought the eliminators in hopes it would clear those codes, but nothing changed, so the eliminators should be installed right. As far as the motor, it doesn't sputter or hiccup and it doesn't feel too sluggish, but it definately runs rich and I'm not getting all the power and efficiency I can. Later I'll check the injectors to make sure the one that's a different color is the same size.

Edit: the front HOS are the new bosch ones and the rears are old OEM, but the rears shouldn't effect gas mileage right?

[yzrider250]

Are the 98 GT injectors a different size than the 04 GT injectors? I don't know if the fact that my electronics are for a 98 and the motor is an 04 if it's not tuned for whatever injectors were used. I didn't do the swap, so I don't know whether or not the previous owner used the 04 or 98 injectors. I'll check the part numbers when I can.

[1996 GT]

What colour injector did you use as a replacement?

[yzrider250]

One is the stock #19 but the other 7 are pink. This is the p# fote-9f593-d9b. I looked up what they were and people said they might be 19-22.5 but no ones really sure. Even if they were 22.5 could that cause a 10mpg loss? Because I have the 98 computer and I'm running the diablosport 93 octane tune, so I'm sure it's tuned for #19 injectors

[yzrider250]

Here's where it shows it Fuel Injector Chart????

[1996 GT]

Yep, you need a another #21 there bud.

[yzrider250]

Well wouldn't it be tuned for #19's cause of the 98 computer? I'm pretty sure the 98 came with the #19's. I don't think changing the one injector would give me much gas mileage

[1996 GT]

If you're on a '98 computer, you should be running ALL #19's, which means you're running 7 wrong injectors.

[yzrider250]

That's what I thought. Are the #19's enough for a bolt on 04? Should I get all the 19's or one more #21 and get it tuned?

[1996 GT]

#19s are more then enough for full bolt ons. Bring them all back to #19's and your car should run much better.