jeepgirl57

Hi, I have a 1990 Cherokee Laredo. I had the fuel pump replaced last month, Yesterday, I replaced the battery ground cable and now the fuel pump isn't working. I replaced the fuel relay, and it's still not working. Anyone have any suggestion?? it turns over strong, but it just won't start.

gat

Unplug the connector to the pump and check the voltage. Also, you can check for fuel pressure by pushing at the Schrader valve in the fuel rail.

jeepgirl57

Thank you I'll give that a try..

Dave51

Start at the beginning. Pull the Fuel Pump Relay and probe 30 in the relay socket. It should be hot all the time.



Keep this handy. You might need it.

http://jeep.avtograd.ru/cherokee/inj.../89jeepefi.pdf

Dave51

Make sure you're testing the right relay. There is misinformation out there about which is which:



Check all the relays to be sure. Check the crank position sensor.

Check the wiring for shorts especially stuff near the exhaust system like the oxygen sensor. Look for workarounds that POs might have done.

Dave51

Also as much of the wiring as you can at the fuel pump for poor contacts, breaks and shorts.

Still got the old fuel pump?

Dave51

Since this problem happened after fiddling with grounds, check all the grounds. Read the cruiser tips:

http://cruiser54.com/

BlueRidgeMark

Exactly. You touched something. Something broke. Recheck your work before you chase anything else.

jeepgirl57

Okay, First off, the schematic is wayyy over my head. I have a working knowledge of car machanics but I am by no means a mechanic.. lol.. From your image of the relays, I replaced the power latch relay instead of the fuel pump relay although the auto parts store said it is the fuel pump relay, I'll have to check and see if it fits in the same space your image is showing. I replaced the fuel pump and filter last month. I'll check the cable again but I feel comfortable with the ground connection, I can hear the additional power in the crank now that its replaced. I drove the jeep to the auto parts, got the new ground cable replaced it and cranked the car and the fuel pump didn't start. I'll check the fuel pump connection but as I said, I drove it, parked it, changed the ground wire and suddenly the fuel pump isn't working. Thank you for your help with the diagrams, the relay one is different from the one I found online. I'll keep you updated.

jeepgirl57

Hi Dave51, Okay, I switched the relays and went back to ground wire, took it off, cleaned around the bolt a bit and put it back on, now I an hear the fuel pump turn on but its still acting like its not getting fuel... I've been having fuel issues since I first got the jeep. When there is an extreme temp change from cold to hot vise versa, I have to tap on the fuel rail like there's a vacuum, just tap on the rail and it would turn right over, but that little trick isn't working now. it just cranks like its not getting fuel. Any ideas??

Dave51

Press that Schrader valve to see if gas comes flying out as per gat. May need to measure the actual pressure later. Check the plugs to see if they have spark. Got a multimeter? Check the fuel injectors to see if they have power. Pull the plugs to see what they look like, especially if they are like totally fried, wet with gas, black, whatever. Feel comfortable about pulling the injectors? I think they're clogged but do that last.

Dave51

Are all the relays good? I think if the bad relay is now in the Latch it won't start either.

Dave51

Assuming the relay was bad to begin with.

jeepgirl57

Strong stream from the Schrader valve, I don't have a spark plug socket or a multimeter … I don't understand, all I did was take off the ground cable and put a new one on.. Frustrated... guess I'm off to Harbor Freight … Thank you...

Dave51

Well, there does seem to be a history of something with the fuel system, so this isn't necessarily out of the blue.

This will be easy enough to narrow down. So you have enough fuel pressure up to the injectors. You'll need to check spark next. There's a couple ways to do this-- either pull a plug, have it grounded to the engine and turn the engine over and watch for the arc; pull a plug wire and place it close to the engine, turn the engine over and watch for spark; or when you pull the plugs and if they're soaked with gas you probably got no spark. BTW don't hold the plug wire while doing this, there's a LOT of volts there.

So if you have spark but the plugs are dry then it's on to testing the injectors. That tapping thing certainly points in that direction.

BTW did you check all the relays? Again, that Latch Relay could be a problem. It's like the equivalent of the later ASD (Ain't Starting Da-engine).

And go to cruiser's site and check ALL the grounds.

A little too early to go to crank position sensor.