Truck died a few days ago immediately after hitting pothole stretch of road. Acted like out of gas but fuel in tank. I went through the horrendous process of dropping the tank and replacing the fuel pump. I replaced the pump only, not the entire fuel sending assembly. Its back together but still won't start. When I turn the key to the on position I don't hear the fuel pump pressurize, just silence. Maybe I did something wrong. Anything else I should check or any suggestions. What a disappointment after all that effort.
CK5
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1991 Suburban acts like out of gas or fuel pump
- Thread starter GaBnn3
- Start date
Are you sure you’re getting power to the pump?
Fuel pump relay?
Check the ground, did you replace the hose between the pump and sender?
Have you checked the inertia switch? Some are more sensitive than others and I have seen big enough pot holes set them off before. Otherwise, ground, relay, fuses.
Thank you all for taking the time to reply. Not sure I'm getting power to pump, but would like to know the best way to check that. I did not know there is a pump relay, will have to figure out where that is. Ground is reconnected but will double check because it's dirty down there. Yes hose replaced between pump and sender. Did not know there is an inertia switch, will also have to figure out where that is. Thanks for the clues, will get on them. Thanks again.
Relay should be on the firewall. I’m not aware of any inertia switch either on these trucks.
Wiring diagram. Get out your volt meter
Chances are you have a loose wire or fuse
Chances are you have a loose wire or fuse
Brother Mark, still helping out. I miss him.
I was trying to think of that, the inertia switch.
Shuts off the fuel pump when it detects an impact.
Safety feature.
You can check fuel pump voltage at the adal (sp?) Plug, I forget which port. I haven't had a tbi rig since 06.
I was trying to think of that, the inertia switch.
Shuts off the fuel pump when it detects an impact.
Safety feature.
You can check fuel pump voltage at the adal (sp?) Plug, I forget which port. I haven't had a tbi rig since 06.
There is no inertia switch on a C/K/R/V.
There is a fuel pump relay and an oil pressure switch. Switch is redundant in case the relay fails, they have zero to do with safety. Failed relay will result in abnormally long cranking times with a cold engine.
The truck will start and run without one or the other, as long as one still works properly.
Pump not priming is an issue. FYI there is a timer on that function, if you cycle the key to check, you have to wait ~15 seconds or so before trying again. But obviously if it doesn't prime the first time you try, it's not likely going to the second time no matter how long you wait.
There is a single red wire hanging off the fuel pump relay. Put 12V directly to that wire and it bypasses both the relay and the switch. You should hear the pump run immediately doing this. If it doesn't, your problem is LIKELY on the fuel tank end. Bad ground, bad connection, bad wire, etc. If you don't hear the pump prime with the key, this should be your first test.
Edit: this oil pressure switch topic comes up fairly often. Can't find the post where I quoted the service manual, but I did find this, which I can't verify. But is inline with what the manual says:
"
*** UPDATED BY TSB 893206E, DATED OCTOBER 90
When the key is first turned ON, without the engine running, the control module will turn the fuel pump relay ON for two seconds. This builds up the fuel pressure to normal operating pressure. If the engine is not started within two seconds, the control module will shut the fuel pump OFF and wait until ignition reference pulses are present. As soon as the engine is cranked, the control module turns the relay ON, which powers the fuel pump. The control module continues to power the fuel pump during engine operation. If the fuel pump relay fails, it is backed up by the oil pressure switch, which continues to operate the fuel pump as long as oil pressure remains above 28.0 kPa (4 psi)."
There is a fuel pump relay and an oil pressure switch. Switch is redundant in case the relay fails, they have zero to do with safety. Failed relay will result in abnormally long cranking times with a cold engine.
The truck will start and run without one or the other, as long as one still works properly.
Pump not priming is an issue. FYI there is a timer on that function, if you cycle the key to check, you have to wait ~15 seconds or so before trying again. But obviously if it doesn't prime the first time you try, it's not likely going to the second time no matter how long you wait.
There is a single red wire hanging off the fuel pump relay. Put 12V directly to that wire and it bypasses both the relay and the switch. You should hear the pump run immediately doing this. If it doesn't, your problem is LIKELY on the fuel tank end. Bad ground, bad connection, bad wire, etc. If you don't hear the pump prime with the key, this should be your first test.
Edit: this oil pressure switch topic comes up fairly often. Can't find the post where I quoted the service manual, but I did find this, which I can't verify. But is inline with what the manual says:
"
*** UPDATED BY TSB 893206E, DATED OCTOBER 90
When the key is first turned ON, without the engine running, the control module will turn the fuel pump relay ON for two seconds. This builds up the fuel pressure to normal operating pressure. If the engine is not started within two seconds, the control module will shut the fuel pump OFF and wait until ignition reference pulses are present. As soon as the engine is cranked, the control module turns the relay ON, which powers the fuel pump. The control module continues to power the fuel pump during engine operation. If the fuel pump relay fails, it is backed up by the oil pressure switch, which continues to operate the fuel pump as long as oil pressure remains above 28.0 kPa (4 psi)."
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Good info here...
So I had the same thing happen to me on my 93 S10 Blazer. I replaced the pump and it didn't work. I then found out it is recommended to replace the harness on the sending unit (the one inside the tank from the pump to the top of the sending unit) at the same time. So I had to drop the tank a second time and replace an $11 part and then it fired right up. Looks like the part for your suburbans is a little different but
I found one on RockAuto for about five bucks.
I found one on RockAuto for about five bucks.
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Adding that to my stash of info.
I am humbled by the wealth of experience and knowledge by all who seek to help this amateur in his time of need. Thanks again.
Best GM guys on the planet here. Some of the best guys period.
So, I got my multimeter and verified the ground is good. Next I made a test lead and connected it between the fuel pump relay lead and the positive battery terminal, while my son listened at the tank. He heard the pump make a noise with the test lead connected. Then I turned the key to the on position with my son still listening. He heard the pump make noise again. So I cranked it but it still won't start. I tried to follow your advice but am now stumped. What did I miss? Perhaps I should replace the whole sending unit?
Now I'd check for spark at the sparkplugs.
If you have spark, remove the air cleaner and see if fuel is being injected while the engine cranks.
You know the pump works, the only thing you don't know that is pump related, is fuel pressure.
But need to make sure you have spark first, because without spark the engine will not get fuel.
If you have spark, remove the air cleaner and see if fuel is being injected while the engine cranks.
You know the pump works, the only thing you don't know that is pump related, is fuel pressure.
But need to make sure you have spark first, because without spark the engine will not get fuel.
MEMO43
1/2 ton status
Have you disconnected the fuel line to the carb/injectors to verify fuel flow (not pressure)
Also check the fuel filter
my truck an 86 would act like you mentioned
it ended up being a clogged fuel filter preventing fuel flow
Also check the fuel filter
my truck an 86 would act like you mentioned
it ended up being a clogged fuel filter preventing fuel flow
Is good practice to replace the fuel filter when doing pump replacement. When a pump fails it can fill the filter with debris, cause a restriction even with a new pump.
Remove air cleaner assembly, inspect the injector wiring at the throttle body. Have your son crank the engine while you watch for fuel spray at injectors. Should see a nice cone shaped pattern spraying.
If not, then troubleshooting the injector system will be next.
If the injector spray is there and decent pattern, check for spark.
If no spark, check for battery voltage at dist, key on. If voltage, replace the distributor. A new ac Delco is preferred over part store rebuilds.
Good luck lets us know what you find and if need be we can walk you through the injector system
Remove air cleaner assembly, inspect the injector wiring at the throttle body. Have your son crank the engine while you watch for fuel spray at injectors. Should see a nice cone shaped pattern spraying.
If not, then troubleshooting the injector system will be next.
If the injector spray is there and decent pattern, check for spark.
If no spark, check for battery voltage at dist, key on. If voltage, replace the distributor. A new ac Delco is preferred over part store rebuilds.
Good luck lets us know what you find and if need be we can walk you through the injector system
Okay! So I may need help with the TBI system. Maybe the potholes had nothing to do with it. I bought a new fuel filter and took a loaner fuel pressure kit with tbi adapter. New filter installed and with the adapter connected on the engine side of the filter I got 12psi fuel pressure. So, no problem with the pump. In order to also listen to the pump first time I used to relay test lead to activate the pump so I didn't have to listen over the starter. Then I confirmed the fuel pressure while cranking it. I checked for spark and have spark. The engine will briefly start when I spray starting fluid into the intake. But it will not start and run otherwise. What next? I've tried to absorb all the advice and came up short of my goal. Thanks again. Will be anxiously awaiting reply.
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