My 99 XJ 4.0 was running just fine, then 2 days ago I tried to start it up and it just cranked away. Crank sounds healthy and it has never had stalling/rough idle problems. I can hear the fuel pump relay kick on and I hear the fuel pump hum and all my fuses are intact. I've been at it for two days now and I'm really at a loss. I have spark at the distributor and spark at the spark plugs and I replaced the distributor cap and rotor just to be safe. I have fuel pressure at the rail, the only abnormality I have found is slight differences is resistance at the injectors. Cylinder 1 is 12.6, cylinder 2 has shown both 12.6 and 13.0, haven't pulled 3 or 4 because it's a pain but 5 and 6 both show 13. I'm not sure if this is outside of spec, I've heard all sorts of numbers online but I've seen between 10.8-13.2 the most. I don't have any of the typical fuel injector or misfire codes, the only code I have is P0132 O2 signal. Again, it was not idling rough at all before so I don't think one or many of my injectors is bad but I could be wrong. I pulled a spark plug to see if it was somehow to wet to spark but it was bone dry. Really running out of ideas, first thing I did was replace the distributor cap and rotor, crankshaft position senor and TPS. Since then I've just been inspecting wires to try and find a short and poking around with a multi-meter but found nothing. This is my daily driver and I've been without if for two days so I'm getting desperate. Any and all advice would be much appreciated.

 

what cps did u use? Pretty common for non oem replacements to be bad out of the box apparently. If the new one didn’t fix it I’d either try another or reinstall the original as sometimes replacing parts that were ok can cause other issues than the original problem.

are u getting pulse signal at the injectors? If that’s in doubt it could be cam position sensor, that controls injector timing.

 

I just got a duralast sensor from Autozone, that could be the problem. Is there a way to check for pulse with just a multi-meter? I've checked to see if I'm getting 12v on either terminal on the injector wiring harness but it shows zero for both terminals. I grounded to multiple known good engine grounds but I'm honestly not sure if that's the right way to do this. I know there is an easy way to check with a test light but I'll have to go buy one tomorrow.

 

to check injector pulse use a noid light. U can probably “rent” one from autozone. Or around $20 on Amazon. If you don’t get pulse at each injector then change the cam sensor. I would reinstall the original crank sensor so u don’t end up masking the original problem.

 

I got the noid lights and did the test. Each connector is definitely flashing but it's faint. It was mid day and the sun was pretty bright some I'm not sure how bright it should have looked but it seemed faint. I went back with the multi-meter to try and see if the connectors were actually sending the right amount of voltage and I found that each power prong was sending .011 volts and the ground was at zero or sometimes .001 volts. I'm unsure if I'm missing something but shouldn't power be 12v? I tested this with the key out and keyed to start and it was the same. I also tested multiple engine grounds so I believe I should have seen 12v if it was getting power but I could be wrong. Could this be an ECM problem or would the cam position senor be stopping all power?

 

From what I’ve heard as long as the noid light pulses the injector is firing. Dim is normal.

It’s easy to go crazy when chasing a problem like this, but try and look at the basics first. It’s usually the simplest things we overlook and end up going crazy with the parts cannon.

we need air/fuel/spark. Air is no problem. Spark is confirmed. You have fuel pressure, but plugs are dry. So fuel doesn’t seem to be getting in. Do you smell fuel in the cylinder? I can’t imagine 6 injectors suddenly clogging without running rough first. What’s your fuel pressure?
maybe pull the fuel hose off the rail and put it into a container and briefly let the pump prime to test flow from the pump?

 

Okay so after testing I now realize I have zero fuel pressure. I checked multiple times over the course of a few days by pushing in the value on the fuel rail and seeing fuel squirt out but clearly this is not very accurate. Must have just been left over pressure. I checked again to see if the relay is kicking on and it is so it's probably my fuel pump or a clogged line. I tried to listen for the fuel pump hum again but I'm not really sure if I'm hearing it or not. I replaced this fuel pump about 2.5 years ago and I haven't put a lot of miles on it since then but it was an auto zone part so I wouldn't be surprised if it failed. Is there a better way to make sure it's my fuel pump without dropping the tank?

 

ya that won’t be accurate, need to see around 40psi I think. U can “rent” gauges that attach to that Schroeder valve to get an accurate read, google the actual spec.
if it suddenly started acting up my money would be on a failed pump unfortunately, clogs tend to cause gradual symptoms rather than just not running. I would test by disconnecting the fuel hose either at the rail or just under the floor before it rises up at the firewall. Slip a piece of hose over it to direct the spray into a bucket and cycle the key on. If the pump is good it should try to pressurize the line which should give a good squirt.

Maybe look at rock auto for the best pump u can find to get longer life, it’s a pain for sure to change.

 

Yeah I'll try taking off the line and checking but I'll bet the pump went bad. Unfortunately I just filled up before it quit so my tank is full to the brim lol going to have to get a hand with that this weekend. Also going to take some time and track down a Bosch pump from what I hear that's the best quality.

 

You can have a listen under the fueltank or in the trunk) while someone turns the key to the ON position (not Start). You should hear it humming for about 1-2 secs.
If not I'd verify you have power to the pump
If you do, verify fuel pressure with a gauge
If too low , thèn replace pump.

 

How is this coming along?