87 k5 blazer wont start

[89Suburban]

yes i do and yes it has an electrical fuel pump.

Yah, I am a dumb ass, I didn't think TBI started until '88. Do you have a wiring diagram?

 

[89Suburban]

 

[Jims86]

there is a system ground next to the thermostat housing coming out of the wire harness.

One of 4 things is happening.
1) The ecm is not getting power. either from the key power, or the constant power from the battery...maybe even both.
2) no ground
3) burnt check engine light...but if this was the issue, the truck should start anyways.

4) bad ecm
Do you have a digital volt meter? If you do, we can walk you through the tests to figure out whats going on.

 

[oneluckypops]

everyone is telling you things to check but some are not explaing WHY to check those things.

The fuel injection system is NOT a complex technology, so dont get frustrated.

Try to explain how it works to you. When you turn the key on you should normally have a 2 second prime to the pump, that signal is requested from the ecm. Then when you start to crank the truck the pump should be receiving its power from the RELAY. After the truck starts and maintains atleast 4 psi of oil pressure, the fuel pump relay will disengage and the oil pressure sensor is now commanding the pump on. 89s posted the schematics above i will try to help you through them.

BLK/WHT wire is your Relay ground. To test that wire simply atach one end of your test light to to positive bettery terminal. If the tester lights then move to the next wire. If the tester does NOT light you have an open circuit on that wire.

ORANGE wire is the constant power supply from the battery, when the relay trips this wire send power to the fuel pump via the TAN/WHT wire. To test this wire simply hook 1 end of the tester to the Negative battery post, and the other end to the orange wire, If the tester lights go to the next circuit, If the tester does NOT light you have an open circuit in that wire (Typically) the fusable link.

DK GRN/WHT wire is the signal wire. when this wire receives power from the ecm it completes the circuit in the relay , which closes the switch in the relay. To test this wire, its safest to use a multi meter when testing leads directly connected to the ecm. But if a test light is all you have then its what you got. Connect 1 end of the tester to NEGative battery terminal, and the other end to the DK GRN/WHT wire, NOW have someone crank the truck, if the tester lights or shows voltage thengo to next wire. If the tester does NOT light then you need to check your ecm or possably your ignition switch.

TAN/WHT wire. like i mentioned before this is the wire that send the voltage to the pump, so to test it atach 1 end of tester to the NEGATIVE battery terminal and the other end to the TAN/WHT wire. Have someone crank the truck again, If the tester lights up. On to the fuel pump connector test. If the tester does NOT light up then you have a faulty Relay.

RED wire. This wire is a fuel pump prime Wire. Basically its there for diagnostics purposes only, you can atach a fused jumper wire to this wire and atach it to the battery Positive post and it should turn the pump on, CAUTION DO NOT ATTEMT TO DRIVE IT with the pump HOT wired like this.

 

[89Suburban]

everyone is telling you things to check but some are not explaing WHY to check those things.

The fuel injection system is NOT a complex technology, so dont get frustrated.

Try to explain how it works to you. When you turn the key on you should normally have a 2 second prime to the pump, that signal is requested from the ecm. Then when you start to crank the truck the pump should be receiving its power from the RELAY. After the truck starts and maintains atleast 4 psi of oil pressure, the fuel pump relay will disengage and the oil pressure sensor is now commanding the pump on. 89s posted the schematics above i will try to help you through them.

BLK/WHT wire is your Relay ground. To test that wire simply atach one end of your test light to to positive bettery terminal. If the tester lights then move to the next wire. If the tester does NOT light you have an open circuit on that wire.

ORANGE wire is the constant power supply from the battery, when the relay trips this wire send power to the fuel pump via the TAN/WHT wire. To test this wire simply hook 1 end of the tester to the Negative battery post, and the other end to the orange wire, If the tester lights go to the next circuit, If the tester does NOT light you have an open circuit in that wire (Typically) the fusable link.

DK GRN/WHT wire is the signal wire. when this wire receives power from the ecm it completes the circuit in the relay , which closes the switch in the relay. To test this wire, its safest to use a multi meter when testing leads directly connected to the ecm. But if a test light is all you have then its what you got. Connect 1 end of the tester to NEGative battery terminal, and the other end to the DK GRN/WHT wire, NOW have someone crank the truck, if the tester lights or shows voltage thengo to next wire. If the tester does NOT light then you need to check your ecm or possably your ignition switch.

TAN/WHT wire. like i mentioned before this is the wire that send the voltage to the pump, so to test it atach 1 end of tester to the NEGATIVE battery terminal and the other end to the TAN/WHT wire. Have someone crank the truck again, If the tester lights up. On to the fuel pump connector test. If the tester does NOT light up then you have a faulty Relay.

Yes, thank you. I couldn't figure how to explain it like this, he needs to confirm all this first. Also OLP, do you know where that inline fuse on the orange wire is located? Is that under the hood or in the cab?

 

[oneluckypops]

Yes, thank you. I couldn't figure how to explain it like this, he needs to confirm all this first. Also OLP, do you know where that inline fuse on the orange wire is located? Is that under the hood or in the cab?

its been way to long since ive had 1 this old to work on, I cant remember for sure where it is.

Thinking it was on the firewall behind the little plastic cover near the junction block though.

 

[Jims86]

No check engine light. can you give me more a list of all the grounds i need to check im not that familiar with this blazer just got it 2 weeks ago. And where is the ecm fuse located? Sorry if im asking so many questions.

OLP, The check engine light needs to be figured out first. If the ecm is not powering up, the fuel system will not prime.

 

[Jims86]

FYI-there is a fuse in the cab labeled "ecm B" that needs to be checked if it has not been already. also look for a fuse marked "Gauge/idle", this is for the "hot fuel module" if the truck has one...its a toss up, some 350's had them, some didnt.

 

[oneluckypops]

OLP, The check engine light needs to be figured out first. If the ecm is not powering up, the fuel system will not prime.

Yes you are correct. If the ecm is not powering the fuel pump will not work. BUT more times then not the SES light not working is probably just a bulb, You know people use to pull the bulbs out of them all the time instead of fixing the problem.

 

[Jims86]

Yes you are correct. If the ecm is not powering the fuel pump will not work. BUT more times then not the SES light not working is probably just a bulb, You know people use to pull the bulbs out of them all the time instead of fixing the problem.

yup...been there, i should have labeled it as the first thing to check.

 

[leyva]

thank you very much for all info i will try it out. and i will let you guys posted on the work.

 

[smurph20]

Have you checked all the fuses either under the dash and the relays on the firewall. If they are all good then it is a short in a wire somewhere. When trying to start the truck do yo uhave oil pressure on the gauge?

 

[dhamp]

There appears to be (in 89S's schematic) a terminal block or junction of some sort just above the fuel pump where the power feed goes from TAN/WHT to TAN. If you're getting output at the relay, but not at the pump, could be a problem there?

 

[ccmf22]

when i had my 87 i had the same damn issue. my problem was the damn plastic tank selector valve bolted to the frame on the passengers side(were the bed and cab meet) i accidentally hit the tank selector switch to the tank i don't use and i flipped the switch back but the valve got jammed to the side not in use, inturn sending power only to that side. i tested with my multimeter the entire system i was getting power all the way till the valve. i pulled the plug for the sending unit on the tank i use but no power.... tested the other side that i dont use and bammm power so i bypassed the valve completely

 

[ccmf22]

this was the same wiring diagram i tried to go by from my haynes manual and i kept wondering why wire colors were different and it kept leading me to dead ends(from the relay to the fuel pump), i found this other diagram online and it was exact ill try and find it and post it,haynes manuals and there famous "typical "tbi setup