Lack of power issue with 93 EX, Multiple ODB Codes

[Fray]

I have been having a problem with the EX recently - after warming up there is a loss of power. I max out at about 30-35 MPH at tops with repetitive hesitations. I tried pulling codes and have:

157
159
177
543
556

Anyone else experience an issue like this with similar symptoms? The mixture of codes has left me quite confused.

 

[MrShorty]

Which ones are KOEO and which are CM codes (review my "notes on pulling EEC-IV codes" thread or the other instructional threads we have here for discussion on how to distinguish KOEO and CM code during the KOEO test)?

All 5 of those codes are related to air/fuel mixture control. Since the first "step" in controlling fuel is getting it up to the engine, I might first focus on the 543/556 codes, which indicate some problem/fault in the fuel pump circuit. If a KOEO code (hard fault), this should be as simple as carefully inspecting the fuel pump circuit for the break. If a CM code (intermittent fault) it may require additional effort to locate the loose connection in the fuel pump circuit.

 

[Turdle]

Yup^^^
Check the connections to the fuel pump relay and fuse. The relay sockets can get loosened with heat corrosion

Then check fuel pressure. You might tape a fuel pressure gauge to the windshield and go for a drive. Pressure should not fall below 30 psi, and actually should rise above that when the gas pedal is floored. More throttle=less vacuum. Fuel pressure should rise when vacuum goes lower--

This thread might be of help also. Bad solder connections on the PCM, or even a bad capacitor might be the problem.

http://www.explorerforum.com/forums/showthread.php?t=384977