2000 Cherokee Sport 4WD. The Jeep starts fine when cold. But when I drive about 5 minutes to a store and return to the car it will not start on the first key turn. It starts after I turn the key a few times for gas priming (or whatever else happens). I replaced the fuel pump last year and the injectors last fall. I just cleaned the throttle body and IAC. Should I look at a sensor or check pressure at the fuel rail?

 

Could be another bad fuel pump. Sometimes things like those can fail even after recent replacement. I'd take a look into the fuel pump and in-tank regulator first. I've heard it can sometimes be an issue with the fuel-rail, sometimes those can get vapor locked. Could also be issues with injectors. Start with the smaller stuff first, since you mentioned you've had issues with the fuel pump before.

 

Check fuel pressure when it has trouble starting first. I expect it to be good.
Try starting it with pedal to the floor next (clear flood mode)- starts up?

It sounds more heatsoak though- from memory the 00 and 01 years were affected more

 

I'd check the NSS. My 1990 has the warm start problem. Hot and cold are fine but not warm. My clue it is the Neutral Safety Switch is that it also hesitates to get in gear when warm.
Try jiggling the shifter, nor even put it into Neutral if it won't start in Park.

- writeup: https://www.cherokeeforum.com/f51/cf-neutral-safety-switch-n-s-s-refresh-how-182998/
- post: https://www.cherokeeforum.com/f2/nss...6/#post2512988

 

Any MIL codes?

I would slap this on:

Amazon

Amazon

cause there was a technical bulletin:

Fuel System - Hot Start Misfire/MIL ON/DTC's/Rough Idle

NUMBER: 18-031-03

GROUP: Vehicle Performance

DATE: Sep. 05, 2003

THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 18-027-02, DATED SEPTEMBER 06, 2002, WHICH SHOULD BE REMOVED FROM YOUR FILES. THIS IS A COMPLETE REVISION AND NO ********S HAVE BEEN USED TO HIGHLIGHT REVISIONS.

SUBJECT:
4.0L Rough Engine Idle After Restart Following A Hot Soak

OVERVIEW:

This bulletin involves the installation of a fuel injector insulator sleeve.

MODELS:
2000-2004 (TJ) Wrangler (Domestic and International Markets)
1999-2004 (WJ) Grand Cherokee (Domestic and International Markets)
2001-2004 (WG) Grand Cherokee (International Market)
2000-2001 (XJ) Jeep Cherokee (Domestic and International Markets)

NOTE: This bulletin applies to vehicles equipped with a 4.0L engine (sales code = ERH)

SYMPTOM/CONDITION:

Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32°C (90°F) or higher. This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder # 3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector # 3 and causes fuel vapor to form within the injector. This in turn may cause a momentary misfire of cylinder # 3 until the fuel vapor is cleared of injector # 3. The insulator sleeve lowers the injector # 3 temperature to a point below which the fuel will not normally vaporize.

DIAGNOSIS:

1. If vehicle exhibits a rough idle, and if a misfire of cylinder # 3 is observed following a 10 to 20 minute hot soak, perform the Repair Procedure.

PARTS REQUIRED

REPAIR PROCEDURE:

1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves about 25-30 mm (1 in.) in length.

2. Install one sleeve around injector # 3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.

3. Confirm sleeve is flush to intake manifold surface around injector.

4. Check injector # 3 wire and ensure that the injector is rotated to a 2 o'clock position (from driver's side of vehicle).

 

Can't hurt, although the pressure regulator issue happens after sitting so cold starts would be an issue. CPS are thermally-sensitive, but would tend to get worse as it got hotter.

I would also check compression just for laughs.

 

Responses:
Compression is 100psi on 2 cylinders, 120psi on 4 cylinders.
There are no MIL codes.
I am not eager to check fuel pressure since the pressure is fine when cold... quick starting even after sitting for several days.

I'll check these:
NSS
pedal to floor - clear flood mode
running ethanol free fuel

 

NSS and Pedal to Floor both had intermittent success. But the hard start problem got worse so even the initial key turn with cold engine is also failing. I finally hooked up the pressure gauge to see a big problem. The pressure is not holding at all. It goes down nearly immediately.

I figure pressure leak could only be at injectors or fuel pump... otherwise I would see a gas leak somewhere. Both were replaced within the last year.

Is there a way to test if the injectors are leaking? Otherwise I'll order a new fuel pump. I think people are recommending Bosch.

 

After reading and thinking it seems like I have a leaky injector because the engine often stumbles after starting. Someone advises to smell the spark plugs to find one that smells like gas. I'll try that this weekend. Let me know if there is any other easy test to find a leaky injector.

 

A normal plug is dry and tan, a leaky injector might actually be wet or at least sooty. Whatever it looks like, it will probably be different from a dry tan plug

 

Were those compression readings taken with Wide Open Throttle ?

 

did you buy "new" chineseum injectors off ebay for cheap?

 

All spark plugs looked tan and dry. They are Bosch injectors (0280155784) from www.motormanfuelinjection.com.

Is this enough diagnosis to rule out injectors causing the difficult starts? Or is there another method for testing injectors for leaks?

 

Auto shop did the compression test a while ago. I don't know if they do it at WOT.

 

I'm more suspicious of the fuel pump check valve than I am an injector.