[redriderjf87]

Ok I've got the notorious backfire/sputtering problem and until I can get to the car this weekend to check some of the easier stuff, I thought I'd get some feedback for the specific situation I'm seeing.

Basically since I've bought the car a couple months ago it's done the backfire pretty much only in 4th or 5th gear between 1500-2000 rpm at low throttle. When it happened I could stop it by getting off and on the gas, which would cause a thud and then back to normal for about 3-5 minutes. Well for the first time just last weekend it started doing it more to the point where it was a constant backfire sound and I could barely hold 65 on the highway. Also the car's always had a difficult start when warm, and seems to be helped by me giving it some gas at start (yes I know shouldn't have to do that for EFI). Not sure if that's actually a separate issue or not.

After picking up an OBDII usb adapter and reading the the codes I saw the attached image. I'm thinking some of these codes could include previously fixed problems (I recently fixed the surging idle with iac and tps replacements). Anyways when I get home this weekend I'm planning to immediately replace the fuel filter and check for exhaust leaks (I seem to get constant 40 psi from the computer but still). Maybe also switch cop's from cylinder 1 or something and see if's causing a misfire issue.

My main question is I think I know a bunch of possible causes from my searching but wanted to know the best order to start diagnosing/replacing things before I just start replacing everything. Does it look most likely like a single bad O2 in bank 1 as the code would suggest? Is it worth it to investigate other things first? Also I've cleaned but not replaced my MAF. I have an O/R H pipe and I know MIL Eliminators for the upstream O2's get rid of the CEL lights (that I have none of) but do they also actually fix related O2 performance issues? Last thing, I can usually smell fuel after driving but my fuel mileage has not been bad at all (20-21 mpg).

Sorry for writing a novel and thanks for any help/discussions.


EDIT: sorry the attachment didn't work, here's the link: http://tjmdiq.sn2.livefilestore.com...reen shot 2011-05-10 at 7.29.38 PM.png?psid=1

 

[Yadkin]

OBD2 helps in diagnosis but old school works every time.

Everything you've described points to engine electrical. If you don't have spark happening at the right time, every time, you won't burn all your fuel. If the situation continues too long the unburned fuel will clog the catalytic converters and then you'll have to replace them.

Electrical components are the least dependable so start with those first, from high voltage to low voltage. In other words, plugs, plug wires, and coil packs. Then proceed to the low voltage systems that control these. Look for wire breaks, loose connections, insulation breaks, poorly done modifications (such as splices), etc.

You didn't say how many miles on the car but the PCV valve and EGR valves don't last forever and have to be replaced after a certain mileage. Look in your maintenance log and replace what hasn't been replaced.

The inspect/ replace sensors staring with the least expensive first (probably the O2 sensor).

Fuel delivery is the next least dependable, starting with sensors and injectors.

The low power at highway speed is the exact symptom that I had when my catalytic converter was clogged after I ignored the other symptoms for too long.

 

[redriderjf87]

OBD2 helps in diagnosis but old school works every time.

Everything you've described points to engine electrical. If you don't have spark happening at the right time, every time, you won't burn all your fuel. If the situation continues too long the unburned fuel will clog the catalytic converters and then you'll have to replace them.

Electrical components are the least dependable so start with those first, from high voltage to low voltage. In other words, plugs, plug wires, and coil packs. Then proceed to the low voltage systems that control these. Look for wire breaks, loose connections, insulation breaks, poorly done modifications (such as splices), etc.

You didn't say how many miles on the car but the PCV valve and EGR valves don't last forever and have to be replaced after a certain mileage. Look in your maintenance log and replace what hasn't been replaced.

The inspect/ replace sensors staring with the least expensive first (probably the O2 sensor).

Fuel delivery is the next least dependable, starting with sensors and injectors.

The low power at highway speed is the exact symptom that I had when my catalytic converter was clogged after I ignored the other symptoms for too long.

Ok thanks this helps. Btw I have an O/R mid pipe which I'm pretty sure has no cats (at least I don't see any). Also the car has just over 72K. I don't really have a good maintenance history since I just bought the car a little under 2 months ago but I will inspect things in the order you mentioned. Also since we have COP's there are no plug wires correct? Last when I inspect the O2 sensor what kind of signs should I be looking for? Or is it a matter of testing these things with a volt/ohm meter (I don't have these yet but I'll probably get them soon enough). I will keep this updated when I get to it this weekend.

Thanks again
Justin

 

[Yadkin]

Yes no plug wires. (My GT was a '98 so before COP.) That's a nice system and eliminates a lot of potential problems.

You can check the plugs for a cracked insulator, fouling, or uneven burn. Or at 72K miles an $4/ each just replace the set. When you take them out line them up in two rows on the bench and look for color and deposition consistency. This gives you a good indication of which cylinder is not doing its job. There are color charts all over the internet, but you're basically looking for an even tan color.

 

[redriderjf87]

Just drove it again a few times this weekend after replacing the fuel filter (good maintenance anyways I figure) and each time I drove it it stuttered for a few seconds pulling up my driveway (in the country so its a few hundred yards long) and was fine after that. Each time I got a cylinder misfire code in the first 1000 revolutions (1 time it was cylinder 1, the other it was cylinder 4) but ran fine the rest of the time. I also got a O2 heater circuit code but nothing on specific O2 sensors so I'm thinking that probably isnt the root cause. I'm thinking of taking the plugs and coils out now, as well as maybe injectors? I just need to set some time to do it, since it looks like you have to take some stuff off to get to coils/plugs (at least on passenger side).

 

[Yadkin]

Don't discount the O2 heater system code. Warm-up is a critical period for engine control systems and if your trouble is resolved after warm-up you may have isolated the problem. Go to obd-codes.com and enter the specific code.

Using the old-school technique again always look at electrical issues first, since they tend to be the least reliable.

 

[redriderjf87]

Ok after driving it a few times and resetting the codes between drives, I'm noticing that the only codes I'm now consistently getting are P0132 (O2 Sensor Circuit High Voltage), P0141 (O2 Sensor Heater Circuit), and either P1131 or P1132 (I've gotten either before and after driving). To save searching 1131 is "Lack of HO2S Switches, Sensor at Lean Limit Conditions" for bank 1 sensor 1, and 1132 is the same but rich instead of lean.

Because it seems to always be specifying bank 1 sensor 1 and any misfire codes I've had have always been in bank 1, I think I'm going to look at replacing this sensor first. Is there a difference between Bosch and NTK for O2's in quality, as theyre both at my auto parts store for the same price. Also will there be issues with an "exact fit" for the cable length for our cars, since I see some other people with other Ford's complaining they were too short. I guess I should just get mine off and check but thanks again for all the help.

 

[JDos1]

Did you say the MIL Eliminators were on the UPSTREAM o2's? If so then there's your problem. You can't run MIL's on the upstream o2's, only on the downstreams. The Upstreams measure your AFR's. If they're on the upstreams, that's your problem. IIRC.

If they're on the downstreams like they should be, then your problem is 90% likely to be faulty upstream o2 sensors. I had the same issue after I pulled a wire on the bank 1 upstream o2 sensor after installing my o/r H last year.

 

[redriderjf87]

I actually didn't look too closely at my downstreams to see if they had Eliminators or whatnot (as far as I know the rears don't actually affect anything except let you know if the cat is bad which I don't have one), but my upstreams look like normal sensors as far as I can tell. I'm planning on replacing the bank 1 upstream sensor next weekend unless I get the hunch that I should replace cops or something else instead (checked plugs today, they look good). Thanks again for all the help, this is a good thread.

 

[JDos1]

That is all that MIL's do. It tricks the computer into believing that the cats are working properly (hence that's the ONLY function of the downstream o2's.) However the upstream o2's control your AFR's. If you do indeed have MIL eliminators on the upstream o2 sensors remove them and I guarantee your problem will be solved.

 

[redriderjf87]

Ok then they must be MIL's at least on the back ones since I don't have a CEL or any codes for rear sensors. I'll check the front sensor asap tomorrow when I get back in town. Btw not to badger anyone for answers, but to help me before I check the car, what length/fit O2 cable should I be looking for on the front sensors (I ask now because I won't have access to the car until later tomorrow)?

Thanks.