1986 Jeep Cherokee with a 2.5 L 4 cyl. Standard transmission. Will start and run for a couple of seconds and die. If I dribble fuel into the TB it will keep running.I have changed the injector, the fuel filter, the CPS is within normal specs. It is as though something shuts off the fuel pump after it starts?Anyone able to help?
Year : 1986
Make : Jeep
Model : Cherokee
Engine : 2.5 L
Hi have you check fuel presure and pump operation?
Yes, the pump comes on when the ignition switch is turned on and delivers a good volume of fuel.
Pressure is at about 12 pounds at the pump
I cannot tell if the pump runs after the engine starts though
if you spray fuel on the throttle will it start and will it stay running as long as you keep spraying fuel in to the throttle?
Yes it will
then you have either a fuel injector problem or a fuel pump problem give me one minute.
I just put in a brand new fuel injector this morning
Is there a way to keep the fuel pump running when the key si turned on? Also, I have been reading about the possibility of a faulty Auto Shut Down Relay, but I am not sure of it;s location
ok fuel presure should be 14 to 15 psi 12 pounds is not enough are you sure is not more then 12 psi?
this can also be the power and signal to the injector do you have a test light?
I cannot take the test plug out of the TB as it is seized, so can only measure at the fuel filter outlet. Are you saying that at the lower pressure it will start and run for a few seconds but not keep running?
And I can only measure for the few seconds that the pump runs whne the ignition is switched on
yes it will.
Is theere any way to jumper any of the relays so that the pump will keep running, so I can measure the pressure more accurately
it will run because presure has accumulated at the rail to build 12 psi enough to start but not enough volume to build that presure again and thats why it stalls volume is built by the pump presure is the accumulated fuel at the rail.
first we need to see if the injector is getting the power and signal while crancking as well when running and see if we loose power or signal when it stalls, do you have a test light.
I put a noid light into the circuit and it pulses while cranking. Yes, I do have a test light
ok if you have a noide light is better
when the engine starts and stalls does the noide light continues to blink as you cranck the engine to start again?
and does it blinks while is running ?
Yes, when I crank the engine to start again it does - I don't know if it does while it's running for the couple of seconds though as I can't get around to see it that fast
can you get some one to cranck the engine while you feed fuel to it and see if the light flikers .
or starting fuel through the throttle as you been doing to get it to start.
i need to see if the injector shuts off wans it starts.
i'll be back let me know then.
Ok - I poured fuel down the TB. As I cranced, the noid light was flashing. As it started the lights may have been flashing but whne it starts it does so at high rpm and the lights looked as though they were on solid. As the engine died and slowed to a stop, the lights were flickering until the engine died
ok, good then there is crancking and running power and ground signal from the computer to the injector and the injector is new, if the injector light goes out before the ingine stalls then i will say the cam sensor or the security system but at this point the engine stalls first and then the power this is a good running fuel signal and computer sistem so the only problem left is the fuel pump valume .
the fuel pump at this point is in question lest check the fuel pump relay here is a picture of its location see if you find it and lest check the conector for powers .
remove the relay turn the key to on and check for powers at the relay there should be two powers with the ignition on.
on mine, I only have 3 relays which are just to the right of the coil
I have power on 2 pins - 87 and 30. 12.2 v on one and 11.92 on the other
good thats battery and ignition now lest check for a ground, conect the red lid to #30 and with the black lid check the other pins with the ignition key to on see how meny grounds are there.
ok - one minute pls
tell me the pin numbers that show a ground.
take your time.
I think I misread the pins. I have power on 30 and 86, not 87. Ground is only on 85
correct direct battery power should be in 30 then ignition power should be at 86 and ground should be at 85, that leaves 87 and 87A touch pin 87 with the black lid cranck the engine see if you get a ground now.
if you dont then try 87A
keep the red on pin 30?
no problem take your time.
red on 30, black on 87 I get 12.12 vdc
That is just with the ignition key on. Let me try while cranking
While cranking I get 10.3 VDC
thats ok 9 volts should be the minimum. this complete relay system and wiring to the fuel pump is excellent no problems there you have the powers ,the ground, the signal from the computer now lest check the relay by replasing it with another relay in the same box just find another relay with the same amount of pins and swith it over then try starting the engine.
Ok - be right back
Same outcome. Starts - runs for a couple of seconds then dies. Tried 3 times. Same result
ok then the relay is not the problem, at this point we check the entire fuel electrical flow and computer signals and found they are in good standards, ignition spark is precent because if spraid with fuel the engine starts, so going back to the fuel problem it seems like the only thing left here is the fuel pump.
Is there any way to keep the fuel pump running with the ignition switch on so I may test volume and pressure properly?
yes you can try jumping the relay remove the relay and jump #30 and 87 this should make the pump stay on while you check presure on the rail
Also, I read somewhere about an Auto Shut Down relay. Does this apply to this year Jeep?
if presure is low try crimping the return line see if presure goes up to al list 35 psi
not for this year modle this only has a fuel relay .
auto shut down relays eliminates spark only not the fuel.
I tried crimping the return line already - no change - so as you say, the fuel pump must not be supplying enough pressure. I will try to jumper the relay tomorrow and test volume and pressure.
One last question. What causes the pump to only run a few seconds whne the key is first turned on?
good , is time to sleep let me know the results tomorrow ,hope this has been educational.
the computer will cycle the f/pump on and of to build up presure on the rail for start up then shuts off waiting for a start signal then turns the pump on again to maintain fuel rail presure.
Yes, you have been very helpful. Thank you so much
talk to you tomorrow thank you.
ase master certified ,and factory certified,also autmotive instructor for 28 years
Hi Ricardo,You were bang on. The rubber hose on the fuel pump was rotted and prevented full pressure. Changed the fuel pump and fittings and it's as good as new.Thank you again for your exper help.Tom
very good news and very glad to have work with someone who follows instructions to the teeth, it was an excellent experience i wish every one would follow instructions as you do. thank you hope we meet again.