cdg123
NAXJA Forum User
- Location
- Wickenburg/Flagstaff, AZ
Well, I'm new to this forum, so I'm going to talk about myself really quick. My name is Craig. I have been working with TLowery04 and his 1989 project Cherokee. I grew up working around Dad's garage, but showed the signs of being the "black sheep" when I bought a Dodge truck instead of a Ford. I eventually became what I am now, a professional carpenter, semi professional welder, and shade tree mechanic, guitar player, photographer, auto body repairman, amateur trap shooter, black powder collecter guy that I am today. I plan to be a high school shop teacher once I recieve my degree from Northern Arizona University.
My college Jeep I bought from the money I made in cabinetry over the summer. It is a 1992 Cherokee 4x4. It is a bone stock Cherokee with the exception of some nice BF Goodrich all terrain tires. It has a little over 72,000 miles showing on the clock, all original.
The Jeep was suffering from having almost zero fuel pressure at the rail, even though the pump appeared to be flowing the correct volume of fuel. We decided to go with the fuel pump because when I actually sat down and thought about it, a faulty regulator usually means fuel pressure that is too high.
Anyway so today I was able to make this aforementioned '89 Cherokee fire, by jumping it. And I don't mean jumping it in the traditional way either. Please excuse my random capitalizations when I make lists of things...
This is what I know:
1) Voltage at the sender is only 5 volts.
2) The Fuel pump requires about 12 volts to start.
3) The wiring to the sender is good.
4) The connection at the end of the sender is good.
This means that something before the connector in the wiring harness that leads to the pump and sender is bad. It could be the positive, common, or both wires, the relay, relay panel, or possibly something else I'm going to get to in a minute.
The next series of tests involves:
1) The fuel pump relay is cycling as it should.
2) The terminals on the relay and in the relay panel are clean and feel like they are making strong contact.
3) The wiper motor relay does not work in the place of the Fuel Pump relay.
4) The Wiper motor relay works, as the intermittant wipers work.
The only thing I'm not positive on is whether or not the wiper motor relay will work in place of the fuel pump relay on this particular Jeep. Many cars you can switch the relays as both the fuel pump and wiper motor require about the same amperage.
What this should rule out is that the relay is not bad. I will try jumping the relay next time I work on this truck, which won't be until I'm back in town on Monday.
So this should mean either the relay panel is bad, or there is a crack in one or both wires in the wiring harness that leads back to the fuel pump.
However I spoke with my dad, a professional mechanic who suggested that it MIGHT be the case that the wiring runs through the oil pressure sending unit. That it is possible that if the vehicle detects no oil pressure, power to the pump could be cut. And further that dirty and coroded terminals could hypothetically cause enough resistance in the circuit to cause the fuel pump not to fire.
Does anybody know if this speculation could be applied to the '89 Cherokee? Does it have an oil pressure fuel shutoff?
Next speculation I was able to dig up on now is that some fuel pumps have a starting voltage of 12 volts but have a resister somewhere in the circuit that is activated shortly after the vehicle is running that cuts pump voltage back to 5 or 6 volts to ensure fuel pump longevity.
What this is leading up to is if our problem is the relay panel or wiring, and given this Jeep's already spotty repair history, we are considering jumping the pump with a semi-permenant cut of switch that will be wired into the cab (most likely under the carpet, or along the fuel line inside some split-loom)
All in all though, when 12 volts of power is jumped to the fuel pump via a dangerous redneck setup, this jeep runs and idles VERY well. I allowed the jeep to warm up long enough for the system to enter it's "open loop" and learn some of its idle parameters before shutting it down for the day and leaving town. The only further thing I think needs addressing is a stumble it has just off of idle, which from my experience feels like a bad MAP sensor signal, due either to a vaccum line, connector, or bad sensor.
Beyond that, I have nothing more to say, other than the bummer is that I think my fuel pressure tester guage from NAPA bit the dust - most likely a positive thing as I can now most likely get my money back for it as it failed for no apparent reason.
My college Jeep I bought from the money I made in cabinetry over the summer. It is a 1992 Cherokee 4x4. It is a bone stock Cherokee with the exception of some nice BF Goodrich all terrain tires. It has a little over 72,000 miles showing on the clock, all original.
The Jeep was suffering from having almost zero fuel pressure at the rail, even though the pump appeared to be flowing the correct volume of fuel. We decided to go with the fuel pump because when I actually sat down and thought about it, a faulty regulator usually means fuel pressure that is too high.
Anyway so today I was able to make this aforementioned '89 Cherokee fire, by jumping it. And I don't mean jumping it in the traditional way either. Please excuse my random capitalizations when I make lists of things...
This is what I know:
1) Voltage at the sender is only 5 volts.
2) The Fuel pump requires about 12 volts to start.
3) The wiring to the sender is good.
4) The connection at the end of the sender is good.
This means that something before the connector in the wiring harness that leads to the pump and sender is bad. It could be the positive, common, or both wires, the relay, relay panel, or possibly something else I'm going to get to in a minute.
The next series of tests involves:
1) The fuel pump relay is cycling as it should.
2) The terminals on the relay and in the relay panel are clean and feel like they are making strong contact.
3) The wiper motor relay does not work in the place of the Fuel Pump relay.
4) The Wiper motor relay works, as the intermittant wipers work.
The only thing I'm not positive on is whether or not the wiper motor relay will work in place of the fuel pump relay on this particular Jeep. Many cars you can switch the relays as both the fuel pump and wiper motor require about the same amperage.
What this should rule out is that the relay is not bad. I will try jumping the relay next time I work on this truck, which won't be until I'm back in town on Monday.
So this should mean either the relay panel is bad, or there is a crack in one or both wires in the wiring harness that leads back to the fuel pump.
However I spoke with my dad, a professional mechanic who suggested that it MIGHT be the case that the wiring runs through the oil pressure sending unit. That it is possible that if the vehicle detects no oil pressure, power to the pump could be cut. And further that dirty and coroded terminals could hypothetically cause enough resistance in the circuit to cause the fuel pump not to fire.
Does anybody know if this speculation could be applied to the '89 Cherokee? Does it have an oil pressure fuel shutoff?
Next speculation I was able to dig up on now is that some fuel pumps have a starting voltage of 12 volts but have a resister somewhere in the circuit that is activated shortly after the vehicle is running that cuts pump voltage back to 5 or 6 volts to ensure fuel pump longevity.
What this is leading up to is if our problem is the relay panel or wiring, and given this Jeep's already spotty repair history, we are considering jumping the pump with a semi-permenant cut of switch that will be wired into the cab (most likely under the carpet, or along the fuel line inside some split-loom)
All in all though, when 12 volts of power is jumped to the fuel pump via a dangerous redneck setup, this jeep runs and idles VERY well. I allowed the jeep to warm up long enough for the system to enter it's "open loop" and learn some of its idle parameters before shutting it down for the day and leaving town. The only further thing I think needs addressing is a stumble it has just off of idle, which from my experience feels like a bad MAP sensor signal, due either to a vaccum line, connector, or bad sensor.
Beyond that, I have nothing more to say, other than the bummer is that I think my fuel pressure tester guage from NAPA bit the dust - most likely a positive thing as I can now most likely get my money back for it as it failed for no apparent reason.
