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occasional no-start... fuel related?

T

tayman

NAXJA Forum User
Location
Niceville, FL
First of all... yeah, I searched... didn't find anything with a similar issue.

so here's the deal. 1990, 4.0L... MOST of the time, my XJ will start right up, no problems. but every now and then (it happened twice today, it's getting worse) it will crank over all I want, and it won't start. I can spray a shot of starting fluid through the airbox, and it'll start up no problem. I can hear the fuel pump turn on, and stop when it creates pressure... it's not the pump (I don't think?). Is it a sensor? I'm having trouble figuring out exactly what this is...
 
If it always starts WITH a shot of starting fuel, you have a fuel delivery problem, pure and simple. Start by changing out your filter if you haven't already done so. Hook up a fuel pressure gauge on the schrader valve on the fuel rail; get readings while engine is running/not running and compare to factory specs. You really need to test here. There are some diagnostics that you could perform on your pump/regulator to further help you isolate this, but my money is definitely on one of those two items; simple fuel pressure testing may tell the story.
 
well... I'm not sure it's NOT the CPS... I replaced it a few months back, but it's really acting like that's what it is. when it's happened, a number of times I've made sure there was fuel pressure along the rail (pressing the valve open, and squirting fuel). for all I know, I need another CPS... How bad is it to take emery cloth to the tip of the sensor? I did that about a month ago... might be part of the issue?
 
tayman said:
well... I'm not sure it's NOT the CPS... I replaced it a few months back, but it's really acting like that's what it is. when it's happened, a number of times I've made sure there was fuel pressure along the rail (pressing the valve open, and squirting fuel). for all I know, I need another CPS... How bad is it to take emery cloth to the tip of the sensor? I did that about a month ago... might be part of the issue?
Click to expand...


did you replace the cps or just take it out and clean it up?

most times its just a bad conection at the wiring harness. next time this happens, unplug/disconnect and reconnect the wiring harness. also check the cps wiring for damage. the wires coming out of the sensor are long and if not routed real well they can rub against the back of the head and get damaged.
 
I'm sticking with a fuel delivery problem. If you are in a NO-START condition and spraying starter fluid allows the engine to start, the problem is not your CPS, it is related to fuel delivery. The starting fluid confirms that your problem isn't spark related. If it was spark related, why would it start with starting fluid?? You need to perform some fuel pressure testing; testing it by pressing the schrader valve is far from definitive.
 
birchlakeXJ said:
I'm sticking with a fuel delivery problem. If you are in a NO-START condition and spraying starter fluid allows the engine to start, the problem is not your CPS, it is related to fuel delivery. The starting fluid confirms that your problem isn't spark related. If it was spark related, why would it start with starting fluid?? You need to perform some fuel pressure testing; testing it by pressing the schrader valve is far from definitive.
Click to expand...

but once the starter fluid burns off, why does it keep running if its a fuel problem? im not saying it not a fuel issue, but if it were a fuel issue, wouldnt the engine stop running once the starter fluid burns off?
 
Fuel delivery performance doesn't have to be all or nothing; one or more of the hardware components can be weak (or partially clogged in the case of a fuel filter). That's why I think fuel pressure testing would be a good strategy. Simple stuff first. If you don't have a fuel pressure gauge, they can be rented pretty cheaply at many parts stores. Tayman, have you changed out the fuel filter yet? That would be the first thing I'd do if it's been a while......
 
I have not changed the filter... I should definitely check that. I may be able to use a fuel pressure gauge if the ROP has one...

In the Case of the CPS, First, I cleaned the old one off, and that worked for a while... but when it started acting up again, I replaced it entirely. it's looking like that's not the case. I'll check my filter.
 
but my question is: why would it only happen every now and then, and not every start?
 
i have a fuel delivery problem on starts, it normally takes about 2 5 second cranks to get her going. when you stop and cut the engine. get out and stand near the back of your jeep, if you hear a sputtering sound. thats your gas getting pumped back in the tank. thats a good indicater that you need to kinker with the fuel system
 
BUT I can hear the fuel pump come on and build pressure..... every time... I'll check it out in the morning... I'll try to check my fuel filter on saturday afternoon.
 
when was the last time you changed the plugs, cap, rotor and spark plug wires and gave the throttle body and iac a good cleaning?

also check the condition of the ground strap to the firewall and clean the ground wire from the main harness to drivers side fender(next to windshield washer fluid resvoir).
 
The grounds are good... I checked them when I was trying to get my idle normal (successfully btw). The plugs, cap and rotor have not been replaced, but they are still in good condition. I can *almost* guarantee that that's not the issue. I didn't get a chance to check anything today... maybe I'll do it now (even though it's dark)
 
well, put in a new fuel filter... the old one was a bit clogged... the new one definitely flows better. the worst thing about the old one was that when I blew through it, air was coming out the seam where it is pressed together! I could blow through it, and feel it on my hands... No Bueno! the weird thing was... when I tried to repeat that, it was air tight again??? you think this could have been my problem???
 
tayman said:
well, put in a new fuel filter... the old one was a bit clogged... the new one definitely flows better. the worst thing about the old one was that when I blew through it, air was coming out the seam where it is pressed together! I could blow through it, and feel it on my hands... No Bueno! the weird thing was... when I tried to repeat that, it was air tight again??? you think this could have been my problem???
Click to expand...


sure it could have been the problem, did it fix it?
 
so far... but I've only started it a few times since... stay tuned for final answer here.
 
well... One full day... no problems...

...but now that I said that, I know it won't start tomorrow morning!
 
Update:

issue has become less frequent after replacing the fuel filter, but it just happened again last night. it took me three tries of shooting starting fluid down the intake to get it started... still haven't gotten to checking pressure, but I can still hear the pump click off when it reaches pressure. Once it fires up, everything is great... I ran a can of seafoam through the tank right after I changed the filter... any suggestions I can try before I get to checking my fuel pressure?
 
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