93 Explorer runs rough when warm

Cold starts are fine and the engine continues to run smooth after reaching normal running temperature.

Vehicle has 133,000 miles. I changed plugs, ign. wires, air filter and added fuel injector cleaner to the fuel tank. Fuel tank level is half. I checked the pcv and it rattles and the hose isn't blocked so I think it's ok. I had bought a replacement but the new one is 90 deg. vs. straight for the original so I didn't change it cause I didn't have extra hose.

I also bought a fuel filter but my Haynes book tells me that the original filter manufacturer claims that it's good for the life of the vehicle, so I haven't yet changed the filter. Also, wouldn't the engine always run rough if the filter was fouled?

The MAF sensor was changed at 123,000 and I don't want to return to the dealer for service. That job cost over $1000 by the time they were done with it and I said - Never again.

Any ideas based upon the above info? Should I try to have it scanned? I don't know where to take it for a scan. How much should a scan cost and can I assume that the tech will know how to do it properly? It's OBD I.

What other sensors or controllers could be causing this problem?

A side note - Prior to changing the plugs and wires, I called a nearby Monro for an estimate. I am so glad that I called first rather than just having them do it and assuming a reasonable charge. The manager told me it would cost $600 to change plugs and wires! He told me that it was such a difficult job. I bought plugs, wire set and dielectric grease for $54. and had them changed in about two hours.

Thanks for reading.

Welcome to the forum!

Yes, start by checking for stored (KOEO) and active (KOER) codes. This site (http://autorepair.about.com/cs/troubleshooting/l/bl_dtcs_37a.htm) will give you some tips on how you can do it in your driveway. If you were able to change the plugs and wires, you can check the codes.

I'd suggest you check the coolant temperature sensor for proper range and check the fuel pressure both cold and hot. It's not uncommon for the electric fuel pumps to cause starting issues when hot, but I'm not sure you'd see a "rough running" condition from a fuel pump. You could always try changing the fuel filter as preventive maintenance (these are NOT lifetime filters like what Chrysler uses) and see if that has an impact if you don't have a fuel pressure gauge.

-Rod

Rod,

I'm missing something re: self-test codes. Where am I going to see the codes from the schematic that you linked to? What is the purpose of the analog VOM in the schematic? Do I record high pulses and convert to BCD?

Also, coolant temp sensor? I've watched the temp gauge and it's always been no higher than midrange. Do you think coolant temp might play a part?

Thanks

You don't need to use the VOM, you can use the other diagram which just shorts out the STI to ground. Once the jumper wire is installed, you turn the key to the "Run" position and the Check Engine Light will blink out codes. For example, blink, blink, pause, blink, long pause would be a code 21 for the ECT out of range. Following the long pause may be additional codes or you may see a single code repeated multiple times.

If you were using the VOM method, instead of watching the Check Engine Light (CEL), you'd watch the needle on an analog VOM. Deflection would be the same as a blink of the CEL, no deflection would be a pause. The pulse may be too quick for a digital VOM to detect, so it's not recommended to use digital VOM for this.

The gauge on the instrument panel likely uses a separate sensor to derive coolant temperature than what the PCM uses, so just because the gauge is giving a reasonable indication does not mean the PCM is receiving a similar reasonable indication. The PCM will adjust spark timing, fuel injector duty cycle, etc. based on the coolant temperature reading provided to it. If the sensor is out of range, it could be screwing up the air/fuel ratio.

-Rod

That is helpful information. I'll try it.
Thank you very much!

have you fixed your truck already? if not, it sounds like oxygen sensor problems,. we had similar simptoms and it end up to be the o2 sensors,. a regular scan tool may not detect that problem,. you need a realtime scaner or monitor to see the readings of the o2 sensors,. good luck.

have you fixed your truck already? if not, it sounds like oxygen sensor problems,. we had similar simptoms and it end up to be the o2 sensors,. a regular scan tool may not detect that problem,. you need a realtime scaner or monitor to see the readings of the o2 sensors,. good luck.

No, I haven't driven it much over the last few days. I've only used about one-half tank of fuel since I added the FI cleaner and I wanted to let it run it's course. I haven't tried to extract the codes yet, either.

The engine has run smooth from cold starts the times that I have driven it. I have not experienced rough idling but I have not started the engine hot.

I will keep the O2 sensors in mind and will report back here with any and all results.

Thanks