jbarboza19

My 86 Iroc 305..tpi..when cold will crank for a long time b4 eventually starting..(my other 86 i notice when i turn on the key i hear the fuel pumping engage..that being said) when i first turn the key on i do not hear the pump engage..i followed the troubleshooting section of the chilton repair manual and i have replaced the fuel pump relay..oil pressure switch..and still no resolve..once car has been started it will restart with no problems..
Any and all suggestions/ideas will be greatly appreciated!!!! TY

OrangeBird

iTrader: (1)

The fact that the fuel pump doesn't run for a few seconds when you turn the key is most certainly a good reason for the prolonged cranking to start . The two things that run the pump are the oil pressure switch and the computer . It sounds like it takes cranking till the oil pressure comes up , and then it starts , looking like the computer's signal to run for a few seconds isn't making it to the pump . What I would do now , after making sure all the fuses are good (both the ones in the regular fusebox under the dash as well as the "hidden" fuses on the right fender behind the headlight) would be to check the computer's signal to the pump to see if it has failed . If you do a bit more searching around these threads , you will find that the fuel pump run signal from the computer can be checked at the ALDL port , I just cant recall which pin the signal appears on . It's possible that the computer has failed in it's output to the pump signal , but it's also possible to be a fuse or wiring problem as well , , , , You'll need to determine if the signal IS in fact being made from the computer , and if all the fuses and wiring are OK , before you'll find the cause . DON'T just go and replace the computer (or anything else) before you troubleshoot why the pump wont run upon key on . You already know that the pump works , otherwise the car wouldn't run . You can be reasonably assured it's not the relay , since you replaced it ( "reasonably" being that it's never a guarentee that the new part is good either ! ) . So most likely remaning things are either the fuses , wiring , or computer itself .

jbarboza19

Thank you for the help, here is what I've done. I swapped out ecm's between cars and problem stayed. I checked all my fuses, I've also placed direct power to the ALDL term g and fuel pump engages. Now I'm completely lost. When you say " check wiring " is there anything particular I should look at? I wouldn't even know where to start this is so out of my comfort zone but any help is greatly appreciated!!!

Tuned Performance

iTrader: (92)

Hook up a fuel pressure gauge to monoter the 2sec prime. This maybe a cold start switch or ninth injector issue.

OrangeBird

iTrader: (1)

When I hear of cold start problems , the cold start injector/switch are the first thing I think of also . However , in this case , the OP has described that the 2 second prime is absent during initial key on , and thus should be diagnosed first . There will be no fuel pressure to monitor if the pump is not receiving it's prime signal .

Now , since the OP has swapped in an ECM that does prime his other car , it's reasonable to assume that the ECM is not at fault . The fuses have all been checked (including the fender mounted ones under the hood behind the passenger's side headlight , correct ?) , and the relay has been swapped . The only other thing in the system is the wiring that brings the prime signal from the ECM to the pump .

Most wiring problems can be found at either a connector , or anywhere that the harness flexes or rubs on surrounding structures .

As a really quick and easy test to insure that it is the lack of the 2 second prime causing the hard start , try this ..... With the car stone cold (in the condition where the hard start happens) , apply power to you ALDL pump run terminal for a few seconds , and then try to start it . If it starts right up , that's proof that the missing prime is the problem . Now you'll have to find out why the ECM's prime signal ain't making it to the pump .

A decent wiring diagram will be most helpful in tracing out the circuit and finding out where the signal is lost .

iroczracer07

iTrader: (2)

crazyjc15

I had a similar problem after i rebuilt my engine and tryed to fire it up for the first time.

heres a quick diagnostic guid to help you out
first make sure the relay has proper power and ground (power should be there at all times via an orange wire)
with the relay disconnected, quickly jump the connector from the orenge wire to the tan/white wire for just a second or so, the fuel pump should engage when you do this. if not trace the tan/white threw the harness and look for any breaks, there are other devices that run during the prime cycle and it is common to see breaks where the wire splits to those devices, and that's exactly what happened to mine.

hope this helps
p.s. hears a wiring diagram to help

jbarboza19

Much appreciation to all that helped me !! The whole time it was two bad relays! Some how in switching the good for the bad I shorted it. All the testing was excellent tools and will e remembered but I was chasing myself and all I needed was two new relays now both cars start as should. Thank you again

OrangeBird

iTrader: (1)

Gotta love a happy ending