mitch500

hey guys,


just recently my 1991 xj 4.0 aw4 started to have some issues. when i start it after sitting for 5 or more hours or specifically in the morning it takes about a minute of cranking. I have to put my foot to the floor and after a long time it will sputter and come to life... When it does its rough for maybe 5 seconds and the idle is steady at about 750rpms. After its fired up and i go on my way it will start every time no problem.

Things ive done in the past 2 years.

-plugs 3000 miles ago champion copper
-wires
-cap/rotor
-coolant temp sensor
-upgraded injectors from programbo


what ive read maybe is that there is a check valve built in with the fuel pump and the fuel is draining back? is this the same on a 1991 as well?

could i have fuel pressure regulator issues or Crank or cam position sensor...

i plan on cleaning the throttle body and ICV tomorrow... Thought id put this online assuming this is pretty common problem?

any info will help Thanks guys!

mitch500

Thought I'd mention once I do get it started it runs great, No stuttering or lag at all, plenty of power.

tjwalker

Yes, you could have a checkvalve problem on the fuel pump. Or even though you've replaced your injectors, one of them could be leaking. If your engine starts "cleanly" after extended cranking, then suspect the fuel pump. If the engine "stumbles" on startup, then a leaky injector is suspect as it takes a few seconds to burn off the leaked raw fuel from the cylinder.

I'd recommend that you perform some basic fuel pressure testing to isolate the root cause. Consult your factory service manual for the exact procedure. Here is more. Definitely try the poor mans prime as that is a quick and dirty test that tells you a lot!
-----------------------------------------------------
A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”

1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.

Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

mitch500

I've tried the key on/off multiple times until it stops priming. It's the same cranking over and over until it finally comes to life.

I recently about a month ago replaced/cleaned battery terminals so I know they are good. I will have the battery load tested.

Tomorrow I will get a fuel pressure tester and see how that goes

mitch500

Ok so I got a fuel pressure tester this morning. Befor I connected it I pressed the shreader valve with a screw driver and nothing came out. So I connected the pressure gauge to the fuel rail and did the poor mans prime about 10 times until the pumped stopped buzzing, I was sitting at 34psi. After I started the vehicle I sat at about 34-36psi the gauge vibrated around a lot between those numbers.... Same psi at operatin temp. However it still took a good 30 seconds of cranking and my foot to the floor to get it started. When it did start it started clean. No real hesitation.

After I shut the vehicle off is would slowly drop to 20psi in about 5 mins or so.

However I did notice after I reset the gauge and prime the fuel rail a few times with out starting it would go up to 34psi then it would drop down to 14psi in about 5 mins.

What do you guys think I should do next?

mitch500

so this morning after letting the vehicle sit for 24 hours i went outside to test fuel pressure again. i connected the pressure gauge to the rail and it read 0 psi, which i assume is normal for sitting overnight, i did one key prime and left the key on accessories to check the gauge and it read 32psi (engine off)... So im assuming the fuel did not drain back through the check valve on the fuel pump.

so i then twisted the throttle body butterfly a couple time just because i wanted to see if it was moving freely and i jumped into the jeep and it fired first try.?? and read 32 psi fuel pressure running... after i shut it down it dropped to about 24 psi in about 10 mins or so and stayed put around there.

i thought maybe this would be a good time to clean the ICV and throttle body which i did and is nice a clean now. is the ICV post supposed to move freely in and out? i pushed lightly on mine but it doesn't go in... didnt want to break it so i just cleaned and reinstalled....

tomorrow morning i will try and start it again and see if it fires up.

Brew

I can relate to this thread, except mine is combined with the thread I started Here:
https://www.cherokeeforum.com/f5/int...erokee-203096/

In that thread, I mention a,b,c steps I take to start the vehicle clean, but for 6 weeks prior, beginning 10/31, I've tried everything & wasn't sure what was working & what wasn't, to get the Jeep started.

Currently, its 26 degrees here. If I got in the Truck, turn the key & immediately cranked the engine, it won't start. I can continue to do that, and get the same result.

But... If I get in the Truck, turn the key On & just wait 5,6...10 seconds or more, I'll then hear PDC Relays click (ASD, ABS, Fuel Pump - I'm not even sure anymore which one it is), then the Fuel Pump will Prime simultaneously. As soon as those two things happen, I can crank the engine & it (usually) will start.

BTW - Should I be hearing the PDC Relays, loud n clear, while inside the cab? 6 Yrs I've owned the Jeep & for the life of me, I can't recall if its part of the New Issue I've been Gifted with or its always been like that & I've drowned it out? Its pretty loud & annoying, trust me.

Since 10/31, I struggled with starting & all too often came real close to draining the battery before luckily, it started. One morning it actually happened & without a charger, I had to call for friend to jump the truck. Just because I was being charged, didn't mean the truck would start. On this day, I got Starter fluid & 1st began spraying it into the intake hose & when that produced no result, I then took it off the throttle body & sprayed on top of the butterfly, and then later, directly inside, with no results.

3 hours had gone by & this time I was going to have my friend crank the engine, while I sprayed into the throttle body (I didn't want to do this, but tried many other things at this point - that day & others before it. I had the hose off the Throttle B, and told my friend to crank, and out of nowhere, it started. I was approaching to Spray Fluid, but it started & startled me, because I wasn't expecting it!

I don't know what was different, except that the hose was off the Throttle Body. I don't know anything about the 91' xj, but my 95' Grand Cherokee 4.0 shouldn't have to ever have the gas pedal pressed at start up. Now, not saying during these 6 weeks I didn't 1st begin trying to ease the pedal as I cranked, or been so frustrated that I was pretty much stomping on it, or holding the pedal to the floor, but in hindsight, none of that was the magic ticket to get it started, during this New Gift of Intermittent Cold Starting.

If & when the truck did start while depressing the gas pedal, the start up was usually rough. So rough, it would strain to start & if I let go of the key before it reached its full start, it would just shut down. You know, seeming like its Gasping / struggling to get Fuel. I've done Fuel Pressure test & my stuff is good & leak down isn't an issue. Which I'm kind of surprised yours read zero, after sitting for 24 hours. Is that right? Mine held a lot of pressure, from one day to the next & Depressing it, sprayed fuel out.

anyway... I've been focused a lot on the Relays & Ignition System, having Thankfully not been coerced or fooled into needlessly changing my Fuel Pump (I'm still hoping that's not the issue). In another thread, TJ mentions something about "starting circuit", which is something I'm unaware of or have read or researched, under a different name? I don't know. I'd like to hear more about it from TJ.

I've owned my Jeep since Nov. 2008 & never had any starting issues until a feeble mechanic tampered with my vehicle. I do snow removal work in the winters, so I'm very reliant on its dependability - when it snows, I need to be out & getting things done for my clients.

Anyway, you'll see in my thread that I'm still seeking to resolve the issue. Until someone else can recommend something I haven't tried or looked into, I'm going have to gut & inspect everything the Feeble Mechanic did to my Jeep.

[spark plugs, wire, cap + rotor, Bank 1 o2, crank shaft sensor, wiring, vacuum hoses, etc.. I have to thoroughly inspect everything, because the bizarro sprayed degreaser all over my engine, without protecting anything, which instantly effected my TPS, by shorting it out. Then when I told him to fix what he broke, he changed a bunch of good parts, only to fix the bad part (TPS) on top of the engine, LAST!

Degreaser & Water without protection - did he effect PCM, PDC - Degreaser sitting on wiring or vacuum hoses? Who knows - I'm almost shocked he didn't use lighter fluid & a match.

By his changing as many Good Parts, its made it harder for me to pin point my starting & idling issues. It makes me sick to my stomach & has consumed much time, $$ & caused much stress. [Good Parts changed = Crank Shaft Position + Bank 1 o2 + IAC + Other 'I don't Knows' about what he did or tampered with. He's all thumbs & I don't trust his thinking, which in my case, was blatant sabotage in attempt to 'pad' the bill]

& none of that accounts for my simple request for a tune up - Is a Spark Plug Cracked or Bad Gap? Wires Compromised? Can the Cap & Rotor only having "contacts cleaned", be the issue? I don't know, but I knew I should of started from the basics, from the beginning, but I was steered away from that stuff, because they were all supposed to be maintained properly, by the guy I now refer to as the Feeble Mechanic.

Anyway, I'm not sure our issues are related, but sure as heck if I didn't go through the hard start phase you're going through. Its only in this past week I stopped cycling the key altogether, realizing if I just Turn Key On & wait - the Relays will Click & Fuel pump will kick & I am good to go. Its still more than I've ever had to deal with, ever before.

Keep this updated - Thanks

Ray Oliver

Take your Dist cap off ,REMOVE set bolt ,PULL whole Disttrbutor out make sure #1 PISTON IS TOP DEAD CENTER,PULL plug invert straw,turn CRANK BY hand with breaker BAR on socket,look down in fist hole THE slot should be 11oclock,5oclockthe mark on CRANK at zero point.NOW YOUR TIMING IS ON MARK,JEEP 4.0 HAD A BAD EXHAUST MANIFOLD SYSTEM NO FLEX AS YOU REV THE ENGINE IT ROCKS,THEY MISSED THIS AT JEEP.80% BET YOU GOT A CRACK ON THE SLANT CARRY OUT PIPE,THIS WILL CAUSE LEAN OX2 SENSOR CODE TAKES LONGER TO START PLUS MISS AND STUMBLE THE IAC IS MESSING WITH TPS BOTH OF THESE ARE TRYING TO A DRESS THE PROBLEM,WHICH PIPE THAT LEAKKS THAT EXHAUST VALVE IS WORN OUT TO CAUSING A LITTLE MISS,THESE ENGINES ARE 80 YRS OLD,KAISER/HUDSON/AMC/CHRYSLER/JEEPTHEY ARE BEAST WHEN EVERYTHING IS JUST RIGHT,DON'T FORGET ONLY USE COPPER PLUGS,THEY PREFORM 100% ON THESE