Hello all

I have a 99 Monter Sport XLS. Currently I'm not getting good gas millage, infact haven't gotten good millage since last winter. Only got 150 miles from a full tank last time I filled it up complelely and only put couple bucks in after that(relying on other car). Got me through a/the murderous Minnesota winter but set out to rectify the problems this fall.

I took off the plenum and replaced all the spark plugs in all cylinders and the wires on cylinders 2,4, and 6 (the previous owner told me he changed the spark plugs and wires on 1,3, and 5 right before I bought it so I didn't replace those wires). Took it to shop and got the throttle body right and it runs alot smoother.

While putting the bolts back in on the plenum I broke the hose connecting part to the EGR vacuum solenoid. There is still a little piece that can connect to the hose but it is not ideal. Then the check engine light came on and now I'm getting a cylinder 3 misfire/random misfire code has appeared.

Bought a new fuel filter and I'm about to replace that to see if that isn't the problem but if that doesn't work does anyone on the thread know the problem I may be encountering before I take it to the dealer.

 

Misfire on a single cylinder is not likely from a bad fuel filter. Check you spark plug wire connections - it may be loose or not fully engaged. Also check/test wire resistance and the spark plug. It is likely that you you'll have to pull the plenum again to do that, but its worth checking at the plug.

As far as the bad fuel efficiency goes it is probably related to something other than plugs and wires. It is most likely result of some of the sensors not working right. Your engine may be stuck in "Open Loop". This can happen if your engine temp sensor is not working right. Start there. BTW, did you pull a freeze frame from your misfire code? What does it say?

Also if engine is working in "Closed Loop" it worth checking to see if your O2 sensors are working. They may be reading a false lean condition and thus calling for extra fuel (which is not needed). This would end up in poor fuel efficiency. It is possible that the extra fuel call is just below the threshold that is needed to activate Check Engine light and that is why it did not yet kick in.

I'd check "Open loop" situation and engine temp sensor first.
If you did not read the freeze frame from the previous code, do the following:
1. fix the misfire
2. warm up the engine (temp gauge on the dash shows normal temp)
3. disconnect MAF sensor plug
This will set Check Engine light and you will be able to see the Freeze Frame on it. Post the numbers here.

 

Thanks my man. i will get right on it today and let you know the results.