1997 Jeep GC 4.0 starts, then Dies, MN Cold

[Lubener]

Originally Posted By: eljefino
Might be a dirty idle air passage or control motor. Did it run well when your foot was lightly on the gas?


Totally agree. The idle air bypass should be cleaned every few years. Responsible for your fast idle operation. Also, thank your mechanic for putting in the 5/30 oil. You'll need it.

 

[niero]

Lubener,
Yeah, it did run normal when I pressed the gas. Thanks for the tip. I'll ask them to clean the idle air bypass next time I'm in.
And that's good to hear about the 5w30. I figured since it was full synthetic it would be too thin for an old engine.


I think that the bad fuel pump is a good bet. When they tested the battery it said to replace. The shop said that they think with the battery on its way out, the throttle control motor wasn't getting the correct charge, and the engine was getting too much air (or maybe it was fuel - which one does Lean Running mean?)

They checked the sensors, and the computer, but no sensor codes came up.
I do remember that last year, about May 2014, it was having a similar problem, only that it was dying at random while driving. Turned out to be a bad crank sensor. (Which means the timing of the cylinders would be off, right?)


As I understand it, the fuel pumps in these era Cherokee and GC's is problematic. It "pulls hard", so to speak, but has always started.
Since the fuel pump is spendy, and I can't replace it at the moment, here's my band aid fix -

Band Aid:
Getting a portable jump starter so that when it's really cold, I don't even bother starting the Jeep on its own. I hook up the jump starter to ease the wear/drain on the battery. That should at least extend the battery life until I can get the pump fixed.

Does that sound like a good idea? Or can that cause other problems?

I know I'm throwing out tons of questions. I really appreciate the help.
I've always loved cars but I don't understand them very well. Mechanical things make too much sense. Thus, they confuse me.

 

[The_Eric]

So when the Jeep died, it would restart and run normally, but only if the throttle was pressed a bit?

If so, then the likely culprit would be the idle air control valve. But that wouldn't cause the lean code- that's more likely a vacuum leak of some sort.

Now if the above is incorrect and it wouldn't start and run, even with the pedal pushed a bit, that combined with the lean code and the miraculous/mysterious recovery would lead me to closely inspect the fuel pump.

 

[Donald]

Originally Posted By: niero
Lubener,
Yeah, it did run normal when I pressed the gas. Thanks for the tip. I'll ask them to clean the idle air bypass next time I'm in.
And that's good to hear about the 5w30. I figured since it was full synthetic it would be too thin for an old engine.


I think that the bad fuel pump is a good bet. When they tested the battery it said to replace. The shop said that they think with the battery on its way out, the throttle control motor wasn't getting the correct charge, and the engine was getting too much air (or maybe it was fuel - which one does Lean Running mean?)

They checked the sensors, and the computer, but no sensor codes came up.
I do remember that last year, about May 2014, it was having a similar problem, only that it was dying at random while driving. Turned out to be a bad crank sensor. (Which means the timing of the cylinders would be off, right?)


As I understand it, the fuel pumps in these era Cherokee and GC's is problematic. It "pulls hard", so to speak, but has always started.
Since the fuel pump is spendy, and I can't replace it at the moment, here's my band aid fix -

Band Aid:
Getting a portable jump starter so that when it's really cold, I don't even bother starting the Jeep on its own. I hook up the jump starter to ease the wear/drain on the battery. That should at least extend the battery life until I can get the pump fixed.

Does that sound like a good idea? Or can that cause other problems?

I know I'm throwing out tons of questions. I really appreciate the help.
I've always loved cars but I don't understand them very well. Mechanical things make too much sense. Thus, they confuse me.

Portable jump starters work best when they are toasty warm. If you leave it in your Jeep and it gets down to 5F (like today in NY) the portable jump starter will not help much.

With respect to portable jump starters, the heavier the better.

 

[Lubener]

I doubt it is your fuel pump. They usually either work or are totally inoperative.I doubt the engine would start in the first place with a bad pump.Fuel filters would show up when fuel demand is up.A weak battery would give some ignition problems too. You did mention slow cranking.That is what I would check out first.

 

[niero]

The_Eric,
Correct. When it first died it took me ten minutes to restart. At that time I did end up having to push the gas pedal a little bit to finally get it going. Then I had to keep tapping the gas so it wouldn't die.


Good point about keeping the jump starter in the cold. But if I kept it in the house, and only used it in the morning, that would probably make the batter last longer, correct?
Would this technique be damaging in any way?


What does it mean that "fuel filters would show up when fuel demand is up?" The filter would throw an error code?

So if the fuel filter was too dirty it could lead to more wear on the battery?

Thanks, all. I just want to make sure I understand as much of this issue as possible, so I know what to fix next to avoid the same problems.

 

[Nick1994]

You can't get a check engine light code for a fuel filter. You've just got to diagnose that yourself. If you haven't changed it it would be a good idea to do so. I've changed several on Cherokee's. They're super easy, driver side right by the tank, 2 hose clamps all you need is a flathead screwdriver, (I don't think there's a clamp that holds them down?) and they're cheap too. It could be restricting fuel.

 

[meep]

armchair diagnosis. lean code? hard start? fuel pressure regulator. It's a mechanical device attached to the end of the fuel rail. about the size of a golf ball. $73 at advanced auto. Getting cold, stiff, not holding enough pressure.

fuel pump would likely either run or not. So the car would run fine or not at all.

CPS--- typical failure and the symptoms could match.... but the lean code pushes me towards fuel system, and the regulators can and do age. good luck. sounds like you need a real diagnosis as some of these items aren't familiar enough to you to identify and truly work through, and we won't really know across a keyboard and screen. good luck!

 

[JamesBond]

I would suspect moisture in the icv has frozen up. I don't remember what the pcv routing is like on the 4.0 but I remember it being a little strange.

Is there a path for moisture from the crankcase to get into icv?

Don't rely on the mechanics suggestion of a lean code, until you see it for yourself.

 

[niero]

Thank you for the tips. I understand you can't really diagnose an issue over the computer, but it definitely helps knowing the options, and what to ask the garage to check and/or replace. It's good to be able to compare what they say with what people on here advise.


What is the ICV?
Would I just replace it, or is there something to keep it from freezing?


I think it would probably be a good idea, as suggested, to just replace the fuel filter, since I don't know if it's ever been done in the last 3 years. And maybe the fuel pressure regulator, as well.

So far it's been running well without issue. I also decided to drive it to work everyday rather than letting it sit in the cold for 2 or 3 days at a time.
So it looks like the best bet is to replace the fuel filter, fuel pressure regulator, and maybe the ICV. I'm glad it's not likely the fuel pump, as I've heard they're really expensive and labor-intensive.

Thank you again

 

[Nick1994]

Originally Posted By: niero
Thank you for the tips. I understand you can't really diagnose an issue over the computer, but it definitely helps knowing the options, and what to ask the garage to check and/or replace. It's good to be able to compare what they say with what people on here advise.


What is the ICV?
Would I just replace it, or is there something to keep it from freezing?


I think it would probably be a good idea, as suggested, to just replace the fuel filter, since I don't know if it's ever been done in the last 3 years. And maybe the fuel pressure regulator, as well.

So far it's been running well without issue. I also decided to drive it to work everyday rather than letting it sit in the cold for 2 or 3 days at a time.
So it looks like the best bet is to replace the fuel filter, fuel pressure regulator, and maybe the ICV. I'm glad it's not likely the fuel pump, as I've heard they're really expensive and labor-intensive.

Thank you again

The fuel pump is a piece of cake to replace on those. My mechanic buddy pulled one on my grandpa's 96' Cherokee to see if he could figure out why the gas gauge wasn't working right, took 10 minutes to get it out. No need to drop the tank.

 

[meep]

ICV Idle Control Valve.

IACV Idle Air Control Valve.

or IAC.

These are a motorized bypass valve mounted on the side of the throttle body. They allow the computer to adjust throttle real time to regulate idle without using the throttle butterfly valve.

the poster for that had a really good suggestion to check it. IIRC, 4 bolts to come off. they carbon up and get sluggish and you have to keep your foot in it to keep it running when this happens, if it gets stuck closed. They can sometimes be repaired by taking them out and cleaning them. just google Jeep IAC cleaning and there's a bunch out there. It's not hard, it's pretty forgiving to pull it and look at it; not a big risk of messing anything up, and cleaning them is pretty simple.

Good call JB

-m

 

[Drew99GT]

If the Jeep IAC is anything like Toyotas, it's very easy to clean without even removing the throttle body; you just remove the air intake duct, remove any vacuum lines that might allow the IAC passages to drain the cleaner, and all you do is spray throttle body cleaner into the inlet side of the IAC in the throttle body, then wiggle the valve back and forth several times to free it up and remove gum and varnish.

I had similar symptoms on my Corolla this winter and cleaning the IAC cured it.

 

[niero]

Thanks meep and Drew99GT.
I'll have a look at some videos and see if it's something I could try. It'd be nice to be able to do at least a couple things myself to save the trouble/cost of taking it to the shop.

Oh, another thing. Is there a type of non-combustible material that I could use as a makeshift heat shield?
I would open the hood and put it directly on the engine when it was sitting out in the cold. It used to have one attached to the inside of the hood but it fell apart.

Thanks

 

[eljefino]

Originally Posted By: Drew99GT
If the Jeep IAC is anything like Toyotas, it's very easy to clean without even removing the throttle body; you just remove the air intake duct, remove any vacuum lines that might allow the IAC passages to drain the cleaner, and all you do is spray throttle body cleaner into the inlet side of the IAC in the throttle body, then wiggle the valve back and forth several times to free it up and remove gum and varnish.

I had similar symptoms on my Corolla this winter and cleaning the IAC cured it.


When I do this (on saturns) I run the engine then cover the idle port with my finger to starve the engine of air, so it opens the idle motor. I then release my finger, it over-shoots the idle, and goes down, exercising the gizmo. I also spritz random amounts of TB cleaner in while torturing the car.

 

[niero]

eljefino,
What is TB Cleaner? Is it easy to find?


Update:
So far, the Jeep has been running well. Once in a while the idle dips down a little lower (it usually idles at the line below 1000rpm, so it's not a big dip.) Any lower and the engine would die, but I've watched it a lot and it's had no problems.

As I can save up money I'm going to have a look into the these:
- ICV, idle air passage and control motor.
- replace the camshaft position sensors, just to be proactive
- fuel filter
- fuel pump regulator
- idle air bypass

Anything else I could look at or replace, just to be safe?



Question: Would the cold air intake have anything to do with this kind of issue, at all?
Maybe getting a full KN air intake (not just the air filter) would be good.

Question: Would an upgraded KN cold air intake benefit the Jeep, or just give it a little more power?

Again, thank you all for the help. I know these are "noob-esque" questions

 

[jeepman3071]

Cold air intakes don't do much for the 4.0L. I have a 62mm bored throttle body which gives a bit more throttle response, but a cold air intake won't do too much. I've done a bunch of testing on various Jeep 4.0s with a few different setups. The best setup I have found for both power and mpg gains is my current setup. I have an Amsoil EA drop-in filter in the stock air box, a 62mm bored throttle body, and a Dynomax Super-Turbo cat back exhaust. Dynomax makes the same exhaust for your ZJ Grand Cherokee. The exhaust flows well without being annoying. It has a tad bit deeper tone than stock while retaining the stock volume.

 

[HankHill]

I'd run with the IAC motor. At least take it off and clean out the passage with Throttle body (TB) cleaner (or use brake cleaner like I do).

The MAP sensor is prone to failure on these motors. Similar to the situation your are describing now. There is a small piece of rubber vacuum tubing that connects the sensor to your throttle body. That can, and will crack, check that also.

The TPS fails also, and ALSO has symptoms just as you describe. Throttle position sensor, on side of TB.

The cam position sensor (in distributor housing), rarely fails.

The CPS (crank position sensor) fails often, say every 80k. When they fail,(most of the time), its a go, no go situation. It just fails, no start, thats it..

I've put around a total of 400k+ on two of these motors, and I've never had a fuel pump fail, or a filter clog, etc..
(change that filter though!!!)

Don't bother throwing your money at parts that aren't broken (yet). Just promised myself I'd say that, as I do it all the time, and wish I wouldn't..

As far as performance for these motors, there's really not much more you can do. Skip the cold air intake, it does nothing. As mentioned, a bored out TB does very little. If you had a mill, I'd say go for it, but paying over $20 for one is a rip.

Headers are "ok". They change the torque curve a little, but with the price and labor, and the blood spilled on the install, and re-install after it cracked after 25k, its just not worth it. Maybe 2-4 hp gain. Maybe.

The most improvement I've FELT, and noticed at the pump, was an injector upgrade. Bought a set of used ford injectors, gained about 4 hp, and got about 1 mpg better.

I'd still have my cherokee if I could keep the bodys from rusting out around the motors.

 

[niero]

Originally Posted By: HankHill
As far as performance for these motors, there's really not much more you can do. Skip the cold air intake, it does nothing. As mentioned, a bored out TB does very little. If you had a mill, I'd say go for it, but paying over $20 for one is a rip.

Headers are "ok". They change the torque curve a little, but with the price and labor, and the blood spilled on the install, and re-install after it cracked after 25k, its just not worth it. Maybe 2-4 hp gain. Maybe.

The most improvement I've FELT, and noticed at the pump, was an injector upgrade. Bought a set of used ford injectors, gained about 4 hp, and got about 1 mpg better.


Just upgrading the fuel injectors can make that much of a difference? Mine are pretty new, within the last year and a half, I think.
Are there specific injectors you'd recommend?

 

[meep]

The ZJ is still to this day my favorite Grand Chero. I absolutely loved the 93 4.0 I had, rare with the AW4 trans. small bits fell apart weekly as it got really old but the drivetrain solidered on and on.