I have 2 known good PGMFI relays that I have, one presently installed on the vehicle. My issue is this: I have to cycle the key at least 3-5 times before the relay will fully energize and start the fuel pump. In other words, the car will need to crank multiple times until the fuel pump circuit is energized. I know the ECU grounds out that circuit. The grounds are all good, and the electrical resistances seem to be fine will all the wires related to this circuit < .3 Ohms of resistance. I think my P28 ecu may be fried. I'm hesitant to remove the cover and see burnt circuit board. So... what I'm seeking here are possible other solutions than what I already know and have overlooked, before replacing and re-chipping my ecu.

Known:
Electrical resistance/continuity are ideal
ECU grounds are clean, secure, and tight.
PGMFI relays are new, and know good.

Unknown:
Fried ECU.
{Please insert relevant info....}

 

sounds more like an ignition switch problem to me.sounds to me like the contacts on the ignition switch are getting bad.

if the ecu really was dead,id think it wouldnt even start even after cycling the key over and over..

 

On a whim, I replaced the ignition switch. The operational condition has not changed. The blue/white starting input wire that goes to the pgmfi relay only has 9.6 volts during cranking which is insufficient to energize the relay fully. After prolonged cranking the voltage will momentarily kick up to B+ and then it will go. This is a weird problem. All grounds are good, and the resistance of this wire from the relay to the ECU and to the fuse box is .6 OHMS.

~ Is it possible that an intermittent crank angle signal could be causing the ecu to limit voltage on cold start-up?

~After the car has turned on, it will crank normally for about 5-7 minutes, after which hard starting will occur again due to insufficient voltage on the blue/white starting input wire. Starting the vehicle after I have driven it for a while becomes more difficult than the initial start-up.

~ I do have a burnt resistor in my ECU, but I am not sure what it controls -possibly the starting input?

~ The injectors all have the same resistance at 2.9 ohms, the resistor box receives the B+ voltage once the relay is energized, as does the fuel pump. The Dizzy power wire is in another circuit but always has B+ voltage. As expected, there is no fuel pressure until the relay energizes.

~ An interesting bit of info is that my 15A ECU fuse #37, in the underhood fusebox, blew one day at random. I get proper voltage through there (B+) and resistance is under .8 ohms.

I need help with this. If you're still confused about what I'm saying I'l supply images. The ecu is a P28 with an OBD1 to OBD0 jumper harness. I've been over my wiring 4 times so far and have corrected any corrosion issues: bottom line is that my wiring is good.

 

One last bit of info: either holding the key in the start position of cycling the key multiple times produces the same effect. It's not a matter of insufficient contact within the ignition switch.

 

you said you checked all of your grounds, i had a problem like this once and it turned out to be the ground on the thermostat housing. its worth a check!

 

I trimmed the grounds going to the thermostat housing, soldered and shrink-wrapped of course, and they now are bolted four inches from the ECU. There is NO question that they are great and TIGHT!


Any more suggestions???

 

Are you just trying to say that when you start the car, it turns over many more times than you think it should?

That just sounds like you have a small leak in the fuel line, typically at the injector.


Have you tried priming the pump a few times before fully turning the key.

 

The post clearly explains this. I have to crank for 20 seconds approx for it to energize the main relay and then turn over. No fuel leak... period. Next suggestion....