wbrockstar
Member
- Joined
- Apr 11, 2015
- Messages
- 13
- Vehicle Year
- 1993
- Transmission
- Manual
Two ?'s ... is the fuel mpg still poor and is the MAF new or used ... What happens with the MAF disconnnected? Most times 'accelerator pump' type reactions are MAF related. The MAF may not be heating up or cooling off properly, or base volts could be off .. leading to incorrect MAF info to the computer. Air flow increases as soon as you goose the pedal, but fuel, in carb circuits/passages, takes a bit longer to get up to speed, thus the momentary enrichment by the accelerator pump helps the transition. Goofy MAF will lead to hesitation on acceleration.
I don't remember if the CTS and ACT sensors have been checked. Coolant and incoming air temps will lead the computer to fiddle with the mix. They'll put out a variable resistance based on temp. The TPS should vary in its output also, IIRC, up to about 1 volt at WOT, and less, in a smooth transition, as the throttle is closed. Ford may have changed from the system I remember.
tom
The tps should actually read close to 1.0 volt at idle then gradually increase to 5.0 volts at wot,not 1.0 volt at wot.The tps vref(supply)wire should read 5.0 volts with the key on/engine off and the signal wire should read 1.0-5.0 volts depending on what position the throttle is in.The ecm supplies 5.0 volts to each sensor,the sensor sends a voltage signal back to the ecm to verify that sensors status and then any leftover voltage that didn't get used by the sensor is sent down the signal return wire.Example::A sensor gets 5.0 volts sent to it by the ecm,it sends a voltage signal of 1.87 volts back to the ecm and the leftover voltage of 3.13 volts gets sent down the signal return.It definitely acts like a defective map/bp sensor,going by all the symptoms that were listed.The OP made a comment that detonation stopped after fueling up with 93 octane fuel and thats due to the fact that higher octane fuel doesnt preignite as easily as lower octane fuel does.Once you locate the source of your problem,there will be absolutely no reason you should need to run more than 87 octane. A defective knock sensor would also cause your issue.It retards ignition timing momentarily when detonation is detected,but when it goes bad ,poor fuel economy and poor performance occurs because instead of the timing being momentarily retarded,its constantly retarded.There are other things that will cause detonation too though,like a defective egr valve,too much compression due to accumulated carbon on the pistons,over advanced ignition timing,vacuum leak and a overheating engine.I would use a propane torch with a piece of hose attached to the gas valve and recheck for vacuum leaks.The egr valve diaphragm and gasket,evp gasket,fuel injector bosses,all vacuum solenoids,throttle body gasket,intake gasket,etc are all areas you need to check,don't just think that vacuum leaks only develop at hoses and fittings.The link below describes the propane method.A vacuum leak is well known as being the #1 cause for lean o2 sensor codes.
http://web.archive.org/web/20131229164247/http://oldfuelinjection.com/?p=93
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