QuestionQUESTION: My Bronco now has about 190K on it but runs smooth and quiet around town, engine still seems strong, very little oil consumption. However for about the last 50,000 miles the engine surges and misses under load at highway speeds (climbing hills especially when towing a trailer), I smell gasoline, and hear soft thumps or pops probably coming from the exhaust system (which I think is excess gas detonating in the catalytic converter). I don't notice any black smoking when this happens and there is only a slight loss of power, although the surging and popping will get worse if I don't slow down. Consequently I seldom take the vehicle out of town and never pull my boat to the lake with it anymore.
Prior to when this started I had some check engine lights but the codes only identified a lean condition. The check engine warning stopped appearing but the problem has persisted. I have not checked the codes since because when I did the information did not allow me to diagnose the problem. I replaced the fuel injection pressure sensor under the advice of a mechanic with no improvement. Seafoam treatment makes the engine run better generally but the problem recurs. I have replaced the plugs, wires, and distributor cap twice and the air filter is clean. There is a little oil spray that accumulates on the breather but I have a new PVC in it. I have had other mechanics tell me to run it on higher-octane gas, replace the coil in case it is malfunctioning when hot, replace the O2 sensors and MAF sensors, and get a valve job. Granted the engine has high miles but there has been no change in performance otherwise since this all started.
ANSWER: I have other directions.But first, are you referring to the seafoam added to a vacuum line? And did this help? If so, I believe you have an intake gasket ready to go down. That is one possibility. The more likely is that you are due to service the timing chain.Your truck does need to run high octane if it has any ethanol at all in it. Look for fueling stations that sell no-ethanol fuel. There out there, just harder and harder to find.
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QUESTION: Seafoam was added to fuel, and the engine did run better (they always do) but the problem recurred, as I recall. It has been some time and now the problem exists as it did then, at least.
I have not run a higher-octane fuel in the Bronco. Out here the oxygenating additive is MTBE, not ethanol. I don't recall having run the truck on an ethanol blend.
If the timing chain was the issue, would it not affect performance at all speeds and loads?
ANSWER: A stretched timing chain is most noticeable under a load. The gas smell has me thinking your purge canister is needing replaced, but that is not performance related. After reviewing your symptoms again, I began to think more that your problem is the MAP sensor, located on the firewall. At the minimum, you should have it tested. However, it's conditions would be present all the time, as to where a timing chain would be more noticeable under a load. How is the idle?
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QUESTION: It idles smooth and strong, but on occasion it seems like the idle speed fluctuates, especially after it has just been started.
AnswerSomething I didn't ask, have you retrieved the codes? If you need a picture or instructions, and cannot reply, send it when you rate my help, I will look, and send you what you need. MAP sensors are not cheap, but with the idle fluctuating, it's a close call. If you unplug the sensor, and notice no change in performance, it is your problem. However, trouble codes should help a great deal in figuring out what is wrong, if it is not the timing chain. Be sure and clean the throttle body and idle air control valve also. I have very detailed instructions on many previous posts. It is a little harder on your truck, but still, routine maintenance.
