Fuel pump relay randomly clicks off & engine dies - Pirate4x4.Com : 4x4 and Off-Road Forum

rockcrawln · 10-03-2008, 01:21 PM

I have a '91 350 TBI that I put in a jeep years ago. The engine has been nothing but awesome. Recently it started to die randomly so I stated doing some investigations and found out that the fuel pump relay is clicking off. Anyone know what would cause the computer to turn off the fuel pump relay? I have replaced the relay and pump for good measure (pump was pretty old). I was also told it could be a bad ignition control module so I replaced that before I found the fuel pump relay issue. So, where should I start? What will make the computer freak out and try to shutdown the engine?

Thanks

Odin K30 · 10-03-2008, 02:03 PM

Are you sure the relay is opening before the engine stalls?

If it is, the PCM may be losing tach signal causing it to open the relay and kill the engine.
Igntion module was a good guess. But a broken wire or bad contact can cause loss of tach signal also.

Are there any DTCs?
Do you have the MIL hooked up?

rockcrawln · 10-03-2008, 02:50 PM

Sorry, but what is a DTC or MIL?

It's kinds hard to tell what's happening first. If it's not the relay where else do you think I should start. It's kind of annoying having a nice jeep that won't run. Thanks for any advise you can give.

FrankenToy · 10-03-2008, 03:58 PM

DTC's are codes, is it throwin' any?

MIL is your "Check Engine Light".

It could be that your oil pressure sensor is on the fritz intermittently, too.

Check for codes first (which is what everyone will tell you).

rockcrawln · 10-03-2008, 04:57 PM

no check engine light and no codes. The oil pressure switch has been unhooked for months. Will the comp kill the engine if it doesn't sense pressure?

Warpig58 · 10-03-2008, 05:23 PM

Quote:

Originally Posted by rockcrawln

no check engine light and no codes. The oil pressure switch has been unhooked for months. Will the comp kill the engine if it doesn't sense pressure?

Yes. The relay has a timer in it to energize the pump for 2 seconds when you turn the key, then waits for oil pressure before re-energizing. If you lose oil pressure while running it should kill the pump for safety.

rockcrawln · 10-03-2008, 05:46 PM

What gets me is the engine will run between 2 and 15 min before dieing. That's why I never really suspected the oil pressure switch as being an issue.

ALEX Bronco · 10-03-2008, 05:56 PM

The engine should run with the fuel pump relay out of the system. The relay is used for initial key on prime,and after you have OP all current is flowing thru the oil pressure switch. Your problem is not the relay, it is with OP switch or associated wiring.

the_experience3006 · 10-03-2008, 07:12 PM

I have to agree with the above post in that the oil pressure switch will run the truck after it hits a threashold (4psi?), but both failing is seriously questionable. Is your ECM intermittently turning off and on? I know it will be difficult to check and in fact a good scan tool might be the best way, but I think that it's powering down. Intermittent stuff like that can often be fixed by just tightening some connections that work loose over 17 years. To test the oil pump switch start the truck and get it running and pull the relay. If the engine continues to run then the issue isn't the OP switch. You could also check continuity, but pulling the relay gives you a good test. If it continues to run the problem is elsewhere like a bad tach signal or a bad connection causing the ECM to stop pulsing the injectors.

10-03-2008, 01:21 PM	#1 (permalink)
rockcrawln Registered User Join Date: May 2004 Member # 30586 Location: Redwood Valley, CA Posts: 1,160	Fuel pump relay randomly clicks off & engine dies I have a '91 350 TBI that I put in a jeep years ago. The engine has been nothing but awesome. Recently it started to die randomly so I stated doing some investigations and found out that the fuel pump relay is clicking off. Anyone know what would cause the computer to turn off the fuel pump relay? I have replaced the relay and pump for good measure (pump was pretty old). I was also told it could be a bad ignition control module so I replaced that before I found the fuel pump relay issue. So, where should I start? What will make the computer freak out and try to shutdown the engine? Thanks

10-03-2008, 02:03 PM	#2 (permalink)
Odin K30 Bad Doctor Join Date: Feb 2007 Member # 86878 Location: South of Heaven Posts: 2,465	Are you sure the relay is opening before the engine stalls? If it is, the PCM may be losing tach signal causing it to open the relay and kill the engine. Igntion module was a good guess. But a broken wire or bad contact can cause loss of tach signal also. Are there any DTCs? Do you have the MIL hooked up? __________________ -Vinny -from Elizabeth Nobody cares about your rigs specs... "Me too" short Crew build /forum/chevy/994394-odins-me-too-short-crew-build.html

10-03-2008, 03:58 PM	#4 (permalink)
FrankenToy Registered User Join Date: Oct 2004 Member # 36822 Location: Toyotaville, just west o' Denver Posts: 1,881	DTC's are codes, is it throwin' any? MIL is your "Check Engine Light". It could be that your oil pressure sensor is on the fritz intermittently, too. Check for codes first (which is what everyone will tell you). __________________ Seems the fools are in charge now and they demand a high tariff... Me

10-03-2008, 05:56 PM	#8 (permalink)
ALEX Bronco Wheeler Join Date: Apr 2002 Member # 11016 Location: maine Posts: 194	The engine should run with the fuel pump relay out of the system. The relay is used for initial key on prime,and after you have OP all current is flowing thru the oil pressure switch. Your problem is not the relay, it is with OP switch or associated wiring. __________________ 66 Bronco 2006 HD2500 Duramax

10-03-2008, 07:12 PM	#9 (permalink)
the_experience3006 Registered User Join Date: Sep 2006 Member # 80052 Location: St. James, MN Posts: 1,703	I have to agree with the above post in that the oil pressure switch will run the truck after it hits a threashold (4psi?), but both failing is seriously questionable. Is your ECM intermittently turning off and on? I know it will be difficult to check and in fact a good scan tool might be the best way, but I think that it's powering down. Intermittent stuff like that can often be fixed by just tightening some connections that work loose over 17 years. To test the oil pump switch start the truck and get it running and pull the relay. If the engine continues to run then the issue isn't the OP switch. You could also check continuity, but pulling the relay gives you a good test. If it continues to run the problem is elsewhere like a bad tach signal or a bad connection causing the ECM to stop pulsing the injectors. __________________ [QUOTE=abig84;9192789]i swear id be gay if it wasn't for all the gay sex that's involved[/QUOTE] [QUOTE=TexasBlake;10305687]She's not that hot. I was just looking for a quick lay and she all wanted to like go on dates and shit. [/QUOTE]

10-03-2008, 02:50 PM	#3 (permalink)
rockcrawln Registered User Join Date: May 2004 Member # 30586 Location: Redwood Valley, CA Posts: 1,160	Sorry, but what is a DTC or MIL? It's kinds hard to tell what's happening first. If it's not the relay where else do you think I should start. It's kind of annoying having a nice jeep that won't run. Thanks for any advise you can give.

10-03-2008, 04:57 PM	#5 (permalink)
rockcrawln Registered User Join Date: May 2004 Member # 30586 Location: Redwood Valley, CA Posts: 1,160	no check engine light and no codes. The oil pressure switch has been unhooked for months. Will the comp kill the engine if it doesn't sense pressure?

10-03-2008, 05:46 PM	#7 (permalink)
rockcrawln Registered User Join Date: May 2004 Member # 30586 Location: Redwood Valley, CA Posts: 1,160	What gets me is the engine will run between 2 and 15 min before dieing. That's why I never really suspected the oil pressure switch as being an issue.

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