87 XJ hard to start - Fuel Pump?

My 87 XJ does not always start and is getting increasingly worse. It acts as if it isn't getting fuel and can always be started with starter fluid. Does this sound like a fuel pump or filter problem from lack of pressure on start?

do you prime the pump for a few seconds before trying to turn the engine over?

could be pump or filter. filter is easy to replace as its external, near the rear drivers side tire.

as for the pump, check fuel pressure with a gauge.

renix engine needs a certain rpm of the flexplate/flywheel to start. if battery has low charge or the battery cables are old, it may take a while to start.

if you give it gas/heavy throttle while under load(in gear and driving), does the engine bog down or shutter? if so, then it may be the pump, but with a renix controlled system, testing the charging system and all the sensors with a meter is the best way to diagnos a problem rather then just guessing.

I normally don't prime it. When it won't start, it is almost as if it is fuel locked. I have put jumpers on it and cranked it continuously and it will never start. I am confident is isn't battery related. It is brand new. 1 little squirt of start fluid when it acts up and it fires right up. Right now it is having trouble 6 out of 10 times. I will try the heavy throttle and see what happens.

Tonight it is getting a new fuel filter to see if it makes a difference.

Last night I didn't get to the filter, but I did check the heavy throttle on the way home. Appears like it responds fine.

"testing the charging system and all the sensors with a meter is the best way to diagnos a problem rather then just guessing." Any writeups on what to check?

keith_b00ne said:

Any writeups on what to check?

Click to expand...

You can start here.
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

The best tool on the site is the search function. Use search words pretaining to the specific sensors you want to test and you will get loads of info.

Here is the newest information. Tried to leave work and it just wouldn't start. After a bunch of tries and a lot of starter fluid it finally started. Took it straight to my buddies shop and we checked the fuel pressure and it read 33 psi and idle. We bleed it off and it restored itself immediately. We bleed it off again, and it started. It read 40 psi when revving. We check the compression, it was 150. Plugs looked good. I am beginning to think that it is a issue when the motor is cold. It will start every time when hot. ????????????? HELP ?????????????????

Temperature sensor not telling the computer to go into rich mode for starting like a choke on a carburetor. Check resistance of the sensor that feeds the info to the computer.

Great idea winterbeater........ Last night I checked the compression again when cold. Down to 140, but still ok. It wasn't starting and I put a new fuel filter on since I had one in the garage and it started up afterwards. So temperamental. I will check the temperature sensor next.

check the condition of the braided ground strap from the head to fire wall and renew its connection to the firewall. sometimes the strap looks fine at the firewall, but will crumble when pulled ot twisted.

try disconnecting the cps wiring harness, clean contact areas with electrical contact cleaner, lube with dialectric grease, and reconnect.

have you checked for spark when it doesnt start? spark should be a blue snapping spark. a weak spark will keep it from starting but it may be enough to start when using starter fluid.

what condition are your battery cables in? my 89 respnded very well when i did a battery cable and grounds upgrade(added another ground strap next to the oem strap), along with a redtop battery. what it did was it enabled the starter to consistantly spin very quickly because there was no voltage loss. getting a constant 12volts to the starter is very important on the renix engine(87-90).

other things i did to get a better start up was a throttle body and IAC cleaning along with a top end/combustion chamber cleaning(i used seafoam through the brakebooster vacumn line). there is also a ground wire in front of the window washer fluid resovoir that i renewed the connection on the drivers side fender wall.

what condition/age are the plugs, plug wires, rotor, and cap in? have you checked that the plugs are still gapped at .035?

Lots of good info and suggestions already posted.

Did you know that the fuel pump gets power from different sources under differing conditions?

1. Key to ON--fuel pump gets 12 volts for 3 seconds from the B Latch relay, bypassing the ballast resistor. The ECU cuts the ground to the relay and stops the pump after 3 seconds if it hasn't received input from the crank sensor.

2. Key to START--fuel pump gets 12 volts from the starter relay when cranking, bypassing the ballast resistor.

3. Key to ON, engine is running from idle to just short of WOT--the fuel pump relay sends 12 volts to the ballast resistor, and the fuel pump gets about 6 volts from the ballast resistor.

4. Key to ON, engine running at WOT--the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Not positive you have the ballast resistor on the 87, and it was eliminated 94+, but the above applies to all years.

Replaced the fuel filter several days ago and am just driving it for the first time. Runs a lot smoother. Time will tell if it helped the starting issues. I use to design filter systems and my thoughts are that that the Jeep is having trouble overcoming the inital resistance.