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Mike S.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 5334
Experience:  ASE Certified Master Technician
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97 chevy tahoe: wont start..spark..fuel pump does not hum

Resolved Question:

my 97 chevy tahoe wont start. it turns over fine but seems to have no spark. fuel pump does not hum either when i turn on the key. i just changed the fuel pump a few months ago, any ideas?? Ignition module?? if so where is it?? would that cause the fuel pump not to hum/prime when key is on?? I changed the fuel pump relay also.
Submitted: 4 years ago.
Category: Chevy
Expert:  AMEDEE replied 4 years ago.
Hello!

Does the check engine light come on with the key in the on position?
Customer: replied 4 years ago.
yes
Expert:  AMEDEE replied 4 years ago.
Oh... i see that you only have accepted 3 answers out of 7. I will leave this question open for other experts.
Expert:  Mike S. replied 4 years ago.
Check the fuses, first of all. Exspecially the ECM #1 Fuse 20A for power in run or start. Check the ECM #B fuse 20A hot at all times. Let me know if they are both ok.
Expert:  Mike S. replied 4 years ago.
In case we need a diagram, click here.
Customer: replied 4 years ago.
will do. got to go to work for alittle while, I will get back to ya!!
Expert:  Mike S. replied 4 years ago.
ok
Customer: replied 4 years ago.
im back. ecm 1 and ecm b are both good.
Expert:  Mike S. replied 4 years ago.

Ok, test for spark.

 

You can make a test plug with a new spark plug and some wire, a mini hose clamp and an alligator clip. First open the spark plug gap to around 0.075" and strip both ends of a 16 gauge wire about 4 foot in length. Attach the mini hose clamp around the threads of the spark plug cause that is a ground and secure it with the mini hose clamp with the bare wire end in between to make a good connection. Next, take the other end of wire and secure to an alligator clip.

Now, you have a test plug. Remove any spark plug boot you want and insert your test plug onto the spark plug wire end you just pulled off and ground the alligator clip. Lay the spark plug in some shade somewhere under that hood and then crank the engine and look for spark. It should crackle with sound and should be blue but red is ok, orange is a little weak. If it can jump that 0.075" gap you should have no problem igniting an engine.

You can also use that to check coils on some vehicles.

Also, there is a red wire at the fuel pump relay. That is the test connector. if you hook a fused jumper wire there from the battery you should hear the fuel pump run.

Let me know what you are missing, fuel or spark or both.

Customer: replied 4 years ago.
no spark and no fuel
Customer: replied 4 years ago.
no spark and no fuel. Would the coil have anything to do with the fuel pump not humming??
Expert:  Mike S. replied 4 years ago.
No the coil has nothing to do with fuel pump. Although the fuel injectors and coil use the same feed wire, the pink. Do you have voltage at the pink wire at both the coil and the injectors? With key or run or start.
Customer: replied 4 years ago.
i'll check. You know if this means anything, I was getting major hesitation when I accelerated a few weeks before this issue now. Maybe the coil finally went out? I have 180,000 on this vehicle. Can I check this with probing using a test light??
Expert:  Mike S. replied 4 years ago.

The coil you can test with an ohmmeter. the voltage to the coil with a 12 volt test light.

For instructions on testing the coil, click here.

Customer: replied 4 years ago.
im still unclear as to why no fuel pump hum with key in on position?
Expert:  Mike S. replied 4 years ago.
It only comes on for 2 seconds. there is a red wire at the fuel pump relay. That is the test connector. if you hook a fused jumper wire there from the battery you should hear the fuel pump run.
Customer: replied 4 years ago.
I looked for it and could not come up with it. How do i find red wire?? Coming out of fuse relay box?? With all this cranking over the engine could it be all primed up and just dont come on now??
Expert:  Mike S. replied 4 years ago.
Off the fuel pump relay. You know you should just try a few shots of starting fluid, if it starts with that than you know it is a fuel related problem.
Customer: replied 4 years ago.
we did that and nothing. I am changing the ign coil. Just got back from Napa and doing it now. $48, so if this aint the problem I will go from there. I got to get this running for work tomorrow.
Expert:  Mike S. replied 4 years ago.
Ok, let me know what happens
Customer: replied 4 years ago.
nothing happened any different. still turns over and nothing.:( But I do have a new coil!!
Expert:  Mike S. replied 4 years ago.
Ok, do you have spark coming out of the coil? If not is there power going to the coil? If so then check the primary circuit with the test light on the tach wire or negative side of coil while cranking.
Customer: replied 4 years ago.
ok took out a spark plug and got big time spark. no fuel is happening. The wife said she hit a big pot hole right before parking the night before this happened. Is there a kill switch for fuel somewhere?? I was able to get to the fuel pump plug at the tank, 3 prong plug and tested it for power with key on, run, and did not seem to have any power there??
Expert:  Mike S. replied 4 years ago.
Check for voltage at the gray wire coming off the fuel pump relay with key on for 2 seconds. Check for power to orange wire at fuel pump relay hot at all times. Either jump across the orange wire to gray to test the pump and wiring or hook a fused jumper to the red wire, the prime test lead. If the pump runs then check that the relay is getting a signal with key first turned on at the dark green/white wire, if so replace the relay. If not check the fuses again.
Customer: replied 4 years ago.
how do I get these wires?? do I have to take the fuse/relay box off?? On the fender skirt?? I cant find these wires you talk about. I replaced relay first thing this morning, brand new!!
Customer: replied 4 years ago.
how do I get these wires?? do I have to take the fuse/relay box off?? On the fender skirt?? I cant find these wires you talk about. I replaced relay first thing this morning, brand new!! And went through fuses again all were good.
Expert:  Mike S. replied 4 years ago.
Are you testing the fuses with a test light for voltage present or are you just looking to see if the fuses are ok. You must be sure that voltage is present on both sides of the fuses. If you replaced the relay already then you should be able to find those wires near the relay or the harness near the relay.
Expert:  Mike S. replied 4 years ago.
Are there 4 terminals on that relay? If so, if you remove the relay then at the relay socket you should have voltage at 2 terminals with the key on run. 1 will be the always hot orange wire, the other the dark green/white signal from the ecm when the key is first turned to run for 2 seconds. You could jump it right there from the always hot to the other 2, the prime test connector and the gray wire to test if the fuel pump will run. Then again if you have no power to at least 2 terminals in there you have a problem feeding the relay.
Customer: replied 4 years ago.
testing the fuses with test light. with power on ,run or start. on the coil housing that I took off there was an extra plug of wires ?? The coil had a spark plug wire lead to it and a set of wires in a plug. off to the side of that was another set of wires in a plug. looked like something that could be changed what was that??The relay I changed was in the fuse/relay box where i am finding the fuses you are talking about, is that the relay you keep mentioning?? Is that extra set of wires with the coil the relay?? Maybe I am not looking at the right thing??
Expert:  Mike S. replied 4 years ago.

Actually there are 5 pins on the relay, the other must be the ground.

It should be under the hood most likely on the firewall on passenger side. Let me see if I can find out exactly where it is.

Expert:  Mike S. replied 4 years ago.

Actually its on the drivers side fender. Click here.

The test connector is C8 and the relay is 15.

Customer: replied 4 years ago.
ok, sorry to be such a pain. so i replaced the relay and still nothing......
Expert:  Mike S. replied 4 years ago.
Ok do those tests at that relay.
Customer: replied 4 years ago.
i cannot find the wires!! I replaced the relay and nothing is still happening.
Expert:  Mike S. replied 4 years ago.
Ok, did you locate that C8 prime connector wire. The red wire, you can jump a hot wire to that to check the fuel pump. Then if the fuel pump runs you will then have to check for voltage at the dark green/white wire. You may have to separate the casing on the harness and pull the wiring out to look and see what color the wires are. If you have a 12 volt test light just pull the relay and like I said test for what has voltage with key on run and hot at all times then jump over to the gray or whichever leads to the fuel pump to see if it runs.
Expert:  Mike S. replied 4 years ago.
It's getting late. I need to get some sleep. I'll be back on tomorrow about 8-9 am, I'll see how you are doing then.
Customer: replied 4 years ago.
ok so if runs then what and if not then what??
Expert:  Mike S. replied 4 years ago.
Did the pump run?
Customer: replied 4 years ago.
there are alot of red wires there which one do i jump
Expert:  Mike S. replied 4 years ago.
Look at that diagram, do you see C8? It should be all by itself.
Customer: replied 4 years ago.

there is a cluster of wires. there is a red screwed to the box assuming that is a ground. then another red wire but it is like a battery cable size wire then the cluster. if i have dash lights and no fruel pump dont i just have a bad fuel pump??

Expert:  Mike S. replied 4 years ago.
Its best to test it rather than just replace the fuel pump. Is there any diagram on the relay, sometimes they have a diagram showing how the wiring goes. Do you have a 12 volt test light or voltmeter?
Customer: replied 4 years ago.
TEST LIGHT.
Expert:  Mike S. replied 4 years ago.
Ok, remove the relay and tell me how many terminals in the socket for the relay have voltage with the key on run and hot at all times. Remember 1 wire will only have voltage for 2 seconds so you may want to have someone else turn the key to run. Remember which ones they are. Also, tell me how many total terminals there are.
Customer: replied 4 years ago.

ok will check when I get home at work till noon my time which is 8

;45 now. the relay has 5 prongs. They are numbered 86, 85 30 and such. there is also a diagram on the top of it, with wiring diagram on it

Expert:  Mike S. replied 4 years ago.
Good, that diagram should tell which is the feed to the fuel pump. Ok, let me know when you get home from work.
Customer: replied 4 years ago.
THANKS FOR HANGIN WITH ME!! WHEN I FIND OUT WHICH TERMINAL FEEDS THE PUMP IF THERE IS NO POWER THERE IS IT THE IGN SWITCH?? i CHANGED THE IGN SWITCH ON MY DAUGHTERS 95 TRUCK CHEVY AFTER CHANGING FUEL PUMP FOR NO REASON BUT THERE WERE NO DASH LIGHTS WHEN YOU TURNED ON KEY. tHIS TAHOE HAS DASH LIGHTS WHEN YOU TURN ON KEY.
Expert:  Mike S. replied 4 years ago.
We will have to test the wiring.
Customer: replied 4 years ago.

Thanks I will check it out....

Expert:  Mike S. replied 4 years ago.
I'll be waiting.
Customer: replied 4 years ago.
ok so 87 is hot with key off no other tabs are hot. when you turn key 87 goes off
Expert:  Mike S. replied 4 years ago.
Are you testing at the relay socket? What is 87? Is it marked 87 on the relay? Does any other's go hot when you first turn key to run?
Customer: replied 4 years ago.
number 30 is hot always. touched wire from 30 to battery with key off, sparks and wire got hot quick, no pump action. no other slots where ever hot. Turned key on and put to start not just run and same action with number 30, sparks and hot and no pump. 30 must be the red wire slot??
Expert:  Mike S. replied 4 years ago.
No, don't tough 30 to the battery. If 30 is hot use that to jump to the fuel pump. What were you saying about 87? Where are you getting these numbers from?
Customer: replied 4 years ago.
well I could not ever get pump to react to any of the tabs on the relay so I changed the pump. Trucks runs great. New coil and pump. Thanks for all your help.
Expert:  Mike S. replied 4 years ago.
Ok, glad to hear that. I just wanted to be able to test the fuel pump before replacing it.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 5334
Experience: ASE Certified Master Technician
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