Is there a relay that tells the injection ports to open , etc? 1990 f150 stright six auto, 2wd, duel tank with EFI.Will not start. Have power and is turning over but will not fire. Gas pressure good at fuel rail and fuel pumps both turning on at key turn on BUT stay on which I figured that relay went bad in on position? There is spark to the plugs and when gas is introduced into the throttle body ? it will fire up and run until the gas dissipates. Anyway any suggestions. Have not got any codes yet need test comp. Also if the EEC relay was bad the fuel pumps would not turn on, is that right?

 

True, but when you turn the key to on, the pump should run for 2 sec and then stop, no matter what. It does not sense pressure and run or not run based on that. What is the pressure you are reading on the rail?

 

Sounds like a bad Computer.

 

In bold is your key symptom. Usually this indicates a bad PCM. The fuel pump should turn on for a few seconds, then shut off whenever the key is turned to the Run position.

So X2 for what subford posted above.

A quick test to determine if the PCM is at fault, most likely, or the Fuel Pump Relay is stuck in the On position is to disconnect the PCM then cycle the key On. If the pump turns on then you have a bad relay. If the fuel pump does not turn on then you have a bad PCM.

 

thanks I will check the PCM

 

Pull the codes before doing anything! I learned this the hard way and spent 3 days trying to diagnose a problem plus a couple hundred in parts not really needed. Was given advice here to check the codes and sure enough it pointed me straight to the problem.

 

@rla , I did the test and the pumps did not run so that points back to the PCM?

 

I agree, thanks!

 

I may have been running the truck for quit some time with the pumps running all the time not at the same time but the one that has been selected. So If I change my PCM I may have two correctly working pumps but will it start and run. Is it that the computers just give out eventually and mine finally died?

 

Most of the time when the fuel pumps run all the time with a bad computer then the computer will not ground the fuel injectors. This will allow it to start and then die on starting fluid but it will not start with the injectors.

However if you set along enough with the key on sometimes the pumps will stop and then the engine will start right up.

 

The most common cause of PCM failure is the electrolytic capacitors crack open which allows the acidic fluid inside to leak out which in turn damages the board. The second most common cause is moisture/water damage.

 

Thank you for your help and you were completely 100%right it was the computer. Thanks again.

 

Glad to hear you found the root cause without spending money on needless parts. Thanks for replying back!

 

That's just what happened to mine on Saturday. Being in the electronics field I found all 3 caps (2 - 47uf 16v and 1- 10uf 63v) on an Ethernet and modem computer card. I robbed them to fix my ECC/PCM computer. One leaked so bad I repaired a corroded PCB track. I was fooled into thinking it was the pump and changed it but to no avail. Anyway with 184k on that pump i was worried it would go out soon. No more worries.