Electric fuel pump on 1990 cherokee, 4.0 liter won't turn on.
Approximately 260,000 miles on vehicle. The pump is new. Second one that's been installed since the 230,000 mile mark. Fuel pump relay is good. Battery is new. Vehicle runs fine once the pump comes on, but requires excessive attempts to start when attempting a cold start. The vehicle can be turned off, and then restarted as long as it does not stay turned off for more than a few minutes. The entire electrical system energizes when you turn the switch to ''run'', but the fuel pump does not turn on. During the cold start, when the pump finally does turn on, I sometimes have to hold the throttle a little open to keep it from stalling until it has been running for a minute, and other times the engine will idle to high (between 2000-3000 rpms), but not all of the time. I'm pretty sure that all electrical & vacuum connections are good, but I don't know, I'm not a mechanic, I've only checked what's easily accessible. I can fix it if I can just find out what the cause of the problem is. Any advise would be greatly appreciated. Again it's a '90 Cherokee/ 4.0 liter/ MPI fuel injected inline-6, 5-speed manual, 4-wheel drive. Thankyou.
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Re: electric fuel pump on 1990 cherokee, 4.0 liter won't...
A delay in fuel pump may be due to either a "lazy" relay or an insufficient ground (fender, firewall, or pump itself) It could also be a poor connection at ignition switch. However I took a look at the wiring diagram I have and it seems that there are several items connected to the power supply for the pump, which I see no real reason for even being on that circut at all. Have you tried a code check? Only thing other that I can think of would be the anti-drainback valve in the pump, but the pump should come on and re pressurize the system, not fail to run, even if the valve was bad. To find your problem, you are going to have to do a bunch of testing, till you get an idea what is happening. Just don't assume anything is good till it can be proven to be good. I know I have not "cured your problem, but I hope I've given you enough to go on to begin testing.
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Did you put at least 5 gallons in the tank so the pump will prime properly? Do you hear the new pump running for 1 second when the key is turned to run? Do this remove the Schrader valve core from the fuel supply rail to the injectors on the engine fuel pressure test port (don't loose it) and repeatedly cycle the key from off to run, do not crank the engine, this will help to prime the electric fuel pump, but have at least 5 gallons in the tank before starting the process. Make sure someone watches the fuel pressure test port so when fuel starts to flow you stop the priming process before everything is covered in gas. Also a fuel pump doesn't cause the system you described, an ignition control module and stator cause that and are a known problem in this year of truck. Another problem is the ignition starter switch comes apart.
It is possibly the fuel relay switch found under the hood just above the right wheel well. There should be 4 different relays in line, the second one from the front should be your fuel relay. You can can test by taking another relay and switching them out to see if you have different results. I purchased a new one for around $20 and have not had any problems since.
If you are at or near the 100,000 mile mark then your fuel pump may have failed. If you remove the fuel filler cap and listen carefully at the filler neck while someone turns the ignition key to "run" [don't actually crank the engine] you should be able to hear the fuel pump buzz for about a second and a half as the key is turned On. If you don't hear the pump buzz then odds are your pump is dead. Your pump may have actually failed making it appear as though you ran out of fuel. Not to uncommon. Hope this helps and good luck!
I had a problem with a 1990 once that was strange like that. Went through 4 pumps before finally figuring out that the baffle inside the tank had come free and was knocking the pump around causing it to short. Inside that metal tank isa baffle set up to reduce the splashing around and movement of the gas at teh pump. If it comes free it will knock up against the pump and short it out. When you pull the pump out use a wire to reach around inside the tank and see if you can find a part moving around freely, if you do the only choice if to replace the tank. There is no way to weld that back or reattach it safely, J-B weld won't work and obviously welding is not an option.
you have a fuel pump relay . Check to see if the fuel pump is humming when you turn key. check for proper ground for fuel pump. try spraying some carb cleaner into the intake then attempt a start. The engine will run for a few seconds, this will verify spark. corosion at the electrical connections is always a possibility. and lastly can you get the engine running by opening the throttle when starting?
Of course you will need to check to see if the fuel pump is actually pumping, or damaged. I suggest that you remove the fuel filler cap, then have someone turn the ignition switch on while you listen through the fuel fill inlet to see if you hear the pump turn on for a few seconds then off. If you're hearing nothing and have no fuel, either the vehicle is not telling the pump to turn on, (verify voltage at the pump electric connection) or the pump is bad.
Generally, when you turn the ignition on, you should hear the pump for a second or two as it builds pressure, after replacing the fuel filter, you may need to do this several times to get pressure to the injectors, and to do that, just cycle the switch to on, then off, in 4 or 5 second intervals. The pump if working, will build pressure eventually allowing the vehicle to start. No need to crank, until you have fuel pressure, Just to "ON", then "OFF" several times.
I hope that you took the time to put some fuel injector cleaner (1/2 filled w/Gumout) into your new fuel filter when replacing it, it's a cheap fuel injector/fuel system cleaning method I've used for years when replacing fuel filters. It can cause a sputter or two initially, but does a good job.
My 98 Cherokee was the exact same. I used to have to turn the key back and forth 3 times and then it would start. Otherwise it would just crank and crank for a while and then start. Pretty embarrassing! Took it to the dealer and they said that my fuel pump was losing pressure. I changed the fuel pump and I don't have to prime the pump anymore.