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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: Irish_Alley on December 01, 2014, 01:26:51 pm
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91 v3500 350 TBI. Its been acting up lately now its not running. Problem is its not getting and fuel will start and run for a second on starting fluid. Used to take 5 or so seconds to start when cold. Think that was due to a bad fuel pump relay. Replaced it but it didn't fix. Now I find out I'm not getting and power to the fuel pump relay.
Another weird part is the fuel gauge isn't working right now it was right before it wouldn't start but right now no matter if the switch is connected or if its on left or right tank it won't move off 1/8 tank
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Check the 10-amp ECM B fuse. Will it start and run if you feed 12 volts to the 3" red pigtail off the fuel pump relay?
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Injectors are getting signal. Ecm a and b are good
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...Will it start and run if you feed 12 volts to the 3" red pigtail off the fuel pump relay?
Verify that 12 volts is arriving to the fuel pump relay on the orange wire.
Make sure you don't have a loose bulkhead connector.
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12 will start the pump and it will start but once you remove 12 v it will slowly die
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Orange wire has 12
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It used to ark when I put 12 v to the red jumper wire. Now I'm now getting anything and cant hear the pump start up and the engine won't start
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The truck may have more than one problem. "Not running" and the inability to prime the pump is beginning to sound like an open fuel pump feed (Ckt 120) or a faulty fuel pump. Confirm that you don't have a loose bulkhead connector or loose fuel tank sender connector. Unplug the fuel pump relay and jump orange (Ckt 440 - ECM B) to gray (Ckt 120) then check for power on the gray wire entering the bulkhead connector and on the tan/wht wire exiting the bulkhead connector and running to the fuel pump - circuit 120 switches from gray to tan/wht through the bulkhead. For reference study the 1991 Wiring Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/X_9130_1991_GMC_RV_P_Wiring_Manual.pdf), page 91.
If the ECM simply isn't energizing the relay, you might want to take a few minutes to verify the ECM connections, as well.
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idk its dark and raining out now. took my 04 impala to dover de its about a 20 minute drive but i got a laptop from bestbuy, but when i got there my key wouldnt come out of the ignition. its a known problem with the impalas and its a broken wire in the sifter.
but the problem im getting with the truck is the fuel gauge doesnt move no matter what tank you select i know one has 3/4 tank. even with it unhooked it still should default to the left tank and its the 3/4 tank.
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Mine never "defaults" to one side. I have had it stuck in the middle and it was the switch. I pulled it apart to fix it. (tech section)
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when i first had this "as soon as it starts it stalls" problem today i switched tanks to see if it was the problem (from 3/4 full on the left side to 1/8 full on the right) it didnt fix it so i tried to switch back and the gauge would move. went to remove the switch and it came apart as soon as i removed the pigtail. so i pulled my buddys off his 90 r3500. still no difference. but its years since his was used and idk if its any good.
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Try this:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=6537.0
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how did you fix it? did you just clean the contacts? if run two jumpers parallel top to bottom i can bypass the switch right?
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yeah I cleaned the contacts. It was doing what you are describing. Yes you can bypass it.
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ok ill give that a try in the am. then ill have to figure out why my pumps aint priming.
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Well I bypassed the switch gauge still didn't move. Maybe its the valve ? I have another off my buddy's 90 but its unknown condition
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Got to thinking about it. If I bypassed the relay and the pump turned on and got fuel it should stayed running via the oil pressure switch after I unhooked the jumper wire. And the right side tank was the side that was running and its the 1/8 full side.
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Irish are ya throwing any codes from the ecm?-- You can send 12 VDC directly to the fuel pump through Terminal G of the ALDL connector under the dash.
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never bothered to look for codes lol. i know the light works but i didnt even look. i knew the g post un the aldl went to the fuel pump but didnt think it could handle the amps or the real reason behind it
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once i get a bay in the shop clear from the paying jobs ill bring her in from the 32° weather and rain. then ill start with double checking fuses cause now i cant even bypass the relay. then move to what bd said to check for. i really dont want to but i do have a stand alone tcu for the trans and i might put on a carb and distributor and be done. but this is y first tbi in a square and i wanted to try to make it last. but once i go with the cummins i have to do the stand alone anyway
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That can help determine if the pump has failed. disconnecting the fuel line at the throttle body will help check for flow. You don't need ignition on for this check.
Also, the temp sender next to the thermostat can fail and affect the ecm sending a signal to the injectors to pulse.
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theyre getting pulse i checked that with a diode. i have never heard the pump prime before, the pumps both tanks have only worked once the truck was running.
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Are you listening to it or having someone else listen? Are you using the red jumper at the relay just adding power to it?
Have you tried shaking the harness and see if there is as short or broken wire. If you get the TBI running you will not want to convert to carb...
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got it :). i think like bd said it was two problems maybe three. what i did was jump the wires like bd said and took apart the bulkhead tested on the inside of the outside piece and i had 12v with or without the jumper??? then i moved to the switch took an ohms tester to it the switch would work 100% one way and 50% the other sprayed some brake cleaner in it seamed to help but wasnt 100% when you switched tanks.
so i took it apart and scrubbed the grim off the brass and put it together and it worked 100%. put it all back together and turned the key to on, and i heard one pump prime. waited 10 seconds switched tanks and the other side primed not to mention the gauge works again. i think before when i tried jumping the relay i had the switch either disconnected or it was on the bad side so it wouldnt prime or run.
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So you're good now?
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yes between bd (pumps priming) and you (tank selector switch) we got it figured out
thanks guys
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Don't forget your truck probably has the fuel module in addition to the ECM controlling the fuel pump on this truck.
You should probably verify the fuel pump relay is functioning and that you are not simply being energized by the oil pressure switch. Disconnect it and check to ensure the fuel pump relays is functioning on it's own
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so the pumps priming for 5 seconds isnt the fuel pump relay working?
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Well new problem took the truck and dump trailer to the dump. About 10 minutes down the road staying at a constant speed around 40, she just dies. Pulled into a drive way and parked her. Switched tanks still no start. Switched back starts up. So while running I switched tanks again and it stalls out. Switched back and she starts up. Took her to the dump dump the load and when leaving it does the same thing, Then starts right up. It stalls when I'm cruising not stopping or stopped. I'll see if any codes show
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Code 54 flashed 3 times
54- mixture control (m/c) solenoid or circuit (carbureted models)
54- fuel pump circuit (1986 and later models)
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On a side not I can still hear both pumps prime when each tank is selected. But the right one won't start the engine could be out of fuel but I haven't used the couple gallons in it.
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OK so I took it home with the egr solenoid unhooked. Didn't stall once. Got to the shop turned it off cleaned up the trailer and turn the key over. No fuel pump prime but it will start if it cranks a couple more seconds. The tank that wasn't running right turned out to be empty some how so that solved.
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I was just going to ask if you had gas in it. You really need to do the pinpoint tests on the fuel pump relay circuit.
When the key is first turned ON, without the engine running, the ECM 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 ECM will shut the fuel pump OFF and wait until ignition reference pulses are present. On heavy duty models, a fuel module will override the ECM and the fuel pump will operate for approximately twenty seconds. This corrects a hot restart (vapor lock) during a high ambient temperature condition. As soon as the engine is cranked, the ECM turns the relay ON, which powers the fuel pump. The ECM 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).
•A faulty fuel pump relay can result in long cranking times, particularly if the engine is cold.
•An inoperative fuel pump would cause a no start condition. A fuel pump which does not provide enough pressure can result in poor performance.
CHART A-5 - FUEL PUMP RELAY CIRCUIT DIAGNOSIS (ONE FUEL TANK)
CIRCUIT DESCRIPTION :
When the ignition switch is turned "ON", the Electronic Control Module (ECM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving distributor reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops except when a fuel module is used.
The pump will deliver fuel to the TBI unit where the system pressure is controlled to about 62 to 90 kPa (9 to 13 psi). Excess fuel is then returned to the fuel tank.
A fuel module is used on all 7.4L, G van with 5.7L, and all other 5.7L over 8500 GVW engines to correct a hot restart (vapor lock) during a high ambient condition. It is designed to over-ride the ECM two second pump operation and will run the fuel pump for twenty seconds at initial ignition "ON".
TEST DESCRIPTION : Numbers below refer to circled numbers on the diagnostic chart.
1.This procedure applies direct voltage to run the fuel pump. If the pump runs, it may be a fuel pump relay circuit problem which the following step will locate.
2.This step checks voltage from the battery and the ground circuit to the relay.
3.This test determines if there is voltage from the ECM, terminal A1, to terminal "D" on the relay connector.
4.This completes the fuel pump relay circuit but if this diagnosis was used because the engine would not run then oil pressure switch should also the diagnosed.
DIAGNOSTIC AIDS :
•An inoperative fuel module may be the cause of a hot stall/no start condition. Check for power and ground circuit to the fuel module and a complete circuit to the pump from terminal "A". If OK, and the pump does not run for the specified 20 seconds at initial ignition "ON", replace the Fuel Module.
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This is going to be fun. I checked the connection at the ecm it was clean no signs of moisture/rust. Turned key on still no prime. Turned key off and swapped fuel pump relay with another used one. Pump primes and starts. Swapped relays again so the "bad" on was in and it stilled primed.
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been a while so i figured i do a little update. no problems since it stalled at the dump a couple months ago. but the pump would sometimes prime and sometimes not prime. then if i switched tanks while running it would stall out and not start back up till i messed with the tank switch.
i ordered one from napa and went to put it in right in their parking lot and once i removed my old one it was so hot it scared me a little and i dropped it lol. wasnt real hot just wasnt thinking it would have any temp to it. swapped switches and she primes herself when you turn the key on all the time now and no more stalls when switching from one tank to the other