1994 Ford Explorer Malfunction - Engine

Question: Check engine light goes on/off and engine looses power. No response pushing the pedal until downshift kicks in. Problem occurs after driving for 3-4 hours at highway speeds with transmission downshifting, when going up hills for example. Is okay driving all day when not having to downshift. The ignition timing seems like it is retarding and advancing incorrectly on its own. Once the problem starts, continues even in stop and go driving. Have to really punch the accelarator to get going. Switching the engine off for about 10 minutes usually corrects the problem. My service in Mexico is limited. Checked codes but nothing significant (CEL not on at the time). Replaced plugs and wires. Cleaned air filter and MAP. Same problem.

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Technican: Is your explorer from the usa, what I really want to know is if you have our modern emmission and engine control system. It's helpful to know if you have things like a MAF (mass airflow) sensor, egr valve, etc. It still may be helpful to offer the trouble codes you are receiving.

Owner: Thanks for the reply. Car is from US, registered in CA, so it has everything you would expect in the way of smog control. I brought it down here 5 years ago. Noticed the problem of power loss on the trip down. Problem only occurs on long runs, which are infrequent for me, 4-5 times a year. And just so you know, yes I have same problem when it returns North of border. Turning engine off for about 10 minutes resets everything. Will start up again later if it downshifts at highway speeds. Have replaced things like fuel filter, air filter, fuel pump, plugs, wires. Cleaned MAF sensor because that was recommended elsewhere. Service options are limited here, Ford dealer is a joke. Found a guy with tester about 2 years back but he had trouble even hooking it up. Can't really remember codes at the time but nothing that pointed to problem. Difficult to diagnose because it needs to be driven several hours at high speed for it to occur.

Technican: I have heard horror stories of fuel quality in Mexico. While fuel quality obviously wouldn't only show up after long periods of driving, it is possible poor quality fuel is causing a slight restriction on the catalytic converter. If you were able to look at it in darkness and noticed any glowing when the problem was present, this would be a sure sign. It's easier to check with a vacuum gauge or by creating a temporary exhaust leak (for pressure to escape), but in your case the problem is gone after sitting ten minutes so these tests won't help. MAF sensor cleaning was a good idea. While it didn't fix your problem, I'm curious if you noticed any change in performance otherwise. Ford has issued a service bulletin on MAF contimination. For this reason an occasional cleaning is recommended. One note is cleaning will only help to fix a problem with contamination. The sensor can have electrical problem that cleaning will have no affect on. Without proper test equipment, there is no way to know for sure (considering it runs and is only a performance issue). When you saidhe check engine light goes on/off, do you mean it's flashing? Or simply on for a while then back off... If it's flashing this changes everthing. Another thing that comes to mind is a possible problem with the TPS (throttle position sensor). This sensor an important one as well as maf. Whenever you are in the states autozone and advance auto will check trouble codes free of charge.

Owner: I thought gas may have been the issue at first but didn't make sense after awhile. No other problems with engine or performance other than what I have said. Drove to states one time in 5 years and experienced same thing with a tank of Shell. Converter gave up 3 years back and, since they aren't available down here, was replaced with inline muffler. Check Engine lite comes and goes when problem exists, doesn't flash. To me it seems the computer gets confused changing the ignition timing, perhaps retarding it causing power loss then advancing it giving power back, back and forth. Could MAF malfunction intermittantly? Is there an easy check TPS? Thanks for your help.

Technican: MAF sensors surely can malfunction intermittently. If the TPS is not setting a code it's not easy to check without a scanner or a scope. YOur problem is a relatively smoth running engine, and it never cuts out or missfires... correct?

Owner: That is correct. An additional comment. As I said before, once the problem "locks in" it carries over to stop and go driving. Usually idles at normal rpm but sometimes when it is really bad will lug down like it is going to die, but never has. When leaving from a stop, I push the pedal down, down, down with no response and the car not moving until all of a sudden, the revs jump and it takes off. Very disturbing.

Technican: "TPS or MAF sensor is the best guess I can give. You could try to get a can of electro-cool. This or similar products is available at electronics shops like radio shack. It evaporates very quickly to produce a chilling effect. If you could spray the TPS when the problem occurs (you would have to do it before the ten minute window expired) to see if there is a change. If there is you have identified the tps as the problem. You could try other methods of cooling, but it would have to take place within the ten minute window. You could also use a common volt/ohm meter to test the TPS. But this would be difficult in the ten minute time period. If you can find a way to cool whatever is causing the problem (as cooling is probably what corrects the condition) this would be the best course I diagnosis I can recommend. Without proper diagnostic tools. I've never been to mexico. How is life there, aside from auto service?"

Owner: Thanks for your help. I'm going to try finding those two parts to replace. I have lived in Mazatlan for 5 years now and love it. Weather is wonderful and one of the primary reasons that I came here. Winter temps are about 65-80, you can still wear shorts. Summer only gets up to about 95 degrees but humidity is high, too much for most people that have another place to go. I have only been back to the states about a total of 8 weeks during that time. Some people spend half year here and half year back "home". But you aren't in Kansas anymore. Not any of the 50 states, for that matter. Roads are rough on a body and car, country is poor for the most part, it is dusty and dirty, and prices have gone up a lot while I have been here. There are many things you can't get here and you can't mail order because of duty and taxes. I've already mentioned the lack of auto service. But the resorts and beaches are great and touring the colonial cities in the center of the country can be interesting. If you have never been to Mexico before, give it a try for your next vacation. I would recommend Mazatlan if you live on the west coast. Cancun and Cabo are too upscale for me but thousands love them. and thanks again for the help.

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