ECM/TBI Help

[eblick]

OK I have searched and searched on here and found some info but nothing I have done yet seems to work. My truck was running fine yesterday and then it quit. I thought it was out of gas so put 5 gallons in to get it back running. It wont start. I am not getting the check engine light when I initially turn the key on. At first I thought it was a fuel problem but know I am thinking it is electrical somewhere. Fuel pump works if connected to 12V. I also pulled the ECM out and put it in my other truck and the check engine light came on like normal start up so its not the ECM either. I checked all the grounds and they seem good too. I also checked the fuse block and they all look good. Any thing else I can check? Its an 87 350 TBI Suburban.

 

[ryoken]

Is the pump coming on when you turn on the key? sounds like the pump relay....

 

[eblick]

No its not. But it does if I connect it to 12V power. Will that cause the check engine light to not come on? It acts like there is no computer installed.

 

[ryoken]

It's the pump relay... Little black box on your firewall above the passenger side valve cover....

I always keep a spare in my console...

 

[diesel4me]

Truck has several "spares"!!..

It's the pump relay... Little black box on your firewall above the passenger side valve cover....

I always keep a spare in my console...

I recently learned from a friend that most vehicles that use relays on the electric fuel pumps share the same # relay as the one for A/C or power door locks,etc,and you can swap them around in a pinch,to limp home if one fails!...I got a lady that stalled out on a hiway exit ramp going again by swapping a different relay in place of the fuel pump one on her Ford Crown Vic by using this trick...she was VERY appreciative! ....

 

[eblick]

I just swapped out relays and it still wont start. Is there a way to see if the computer is powered up? I am still not getting the check engine light like a normal start up.

 

[sweetk30]

even with a bad relay at fuel pump cerkit you should still have check engine light. the lack of the light not cycling is the first place you should look.

 

[eblick]

Ok I just pulled out the plugs to the computer and there is power to the computer at pins A6, B1 and C16. Where do I look next? I am getting very frustrated.

 

[sarasotausmc]

Try the fuel filter. My truck sat for nearly a month with the same problem. If it's not the problem, it cost you $2.50 and 5 mins of work.

 

[ryoken]

Well, if the fuel pump isn't coming on when the key is turned on, your problem lies there... You need to check power to that relay.. IIRC the only 2 things that will prevent power to that are the fuse (have you checked the ECM 1 or b fuses?) and the low oil pressure switch... If Dorian chimes in, he will remember...

 

[eblick]

Both fuses are good and there is power to the computer at the ECM. Going to go back oout there with my girl so I have an extra set of hands to trace wires.

 

[ryoken]

Pull that pump relay out and put a test light to the feed for it...

 

[eblick]

OK just checked for power at the pump relay and there is no power when turning the key on. Does anyone know the whole electrical sequence? I changed computers thinking that would fix it and still no luck. There is power going to the computer. What am I missing?

 

[sweetk30]

Try the fuel filter. My truck sat for nearly a month with the same problem. If it's not the problem, it cost you $2.50 and 5 mins of work.

sorry but what does a bad fuel filter have to do with no power to the pump or no check engine light cyclying?

 

[eblick]

If the oil pressure switch is bad would that cause the check engine light to not come on as well as not turn on the fuel pump relay? I am not sure of the whole sequence but from the diagram the oil pressure switch looks like it connects to B2 or fuel pump in on the ECM. It seems I am not getting any voltage at this connection. Does B2 power A1 the fuel pump relay control?

Thanks for all the help so far.

 

[ryoken]

Well, if the fuel pump isn't coming on when the key is turned on, your problem lies there... You need to check power to that relay.. IIRC the only 2 things that will prevent power to that are the fuse (have you checked the ECM 1 or b fuses?) and the low oil pressure switch...If Dorian chimes in, he will remember...

yup

 

[eblick]

Is there a way to test the oil pressure switch? This problem is driving me crazy!

 

[sarasotausmc]

OK just checked for power at the pump relay and there is no power when turning the key on. Does anyone know the whole electrical sequence? I changed computers thinking that would fix it and still no luck. There is power going to the computer. What am I missing?

SweetK30, I posted prior to the above. I thought I had checked everything when I was having problems with mine including the pump, relays, ECM and senosrs, etc... and I didn't, or didn't do it correctly. I also ended up spending more money that I had to. In the end, it ended up being my filter. I overthought the problem I had and offered a suggestion to something. What I ended up doing worked for me. I'd say I'm sorry if you don't like the suggestion I made, but I'm not.

 

[ryoken]

This is just guessing on my part, but, most oil pressure switches are a variable ground switch..

Don't think their is any specifac test for those switches... But I would hook a test light to the positive battery post and touch the sending stud, while off, then cranking...

Hopefully Dorian will chime in here for you because I know he remembers this stuff... I don't have firsthand experience with how that system relates to the pump relay...

 

[eblick]

I disconnected the oil pressure switch on both trucks the parts truck shows around 8 volts at pin B2 while the problem truck is only showing .35 volts or so. I am going to keep back tracking to see where I am losing the power. Also do the injectors go into this sequence at all and if so how? It doesnt look like the are firing either?