Long crank time

In the last few weeks, my 93 XJ 4L has been taking a few seconds longer to crank. Once its started, there are no other symptoms. It runs well. I've noticed that if I let off the key before it fires, it will catch and run sooner.

I remembered reading about this online. http://www.underhoodservice.com/diagnostic-dilemmas-getting-in-sync-with-a-couple-wranglers/

http://www.jeepforum.com/forum/f11/how-reindex-camshaft-position-sensor-1145301/

But these are the newer 4L with a different style cam sensor or sync sensor as some refer to it as, that can be adjusted for slack in the timing chain.

I took off my distributor cap and rotor to see if mine could be adjust but it appears to be non-adjustable unless a new metal bracket is fabricated that locks the rotational position of the sensor. Easy enough but there is no reference marks to get it aligned without an oscilloscope. As far as I can tell, perhaps someone knows better?

I measured the backlash in the timing chain using the marks on the timing cover and have 4* of backlash. I'm assuming brand new is much closer to 0*. There is also some backlash in the distributor gear, as I can slightly rotate the rotor without any cam movement.

I checked the cam sync sensor according to the FSM, and I have 8V reference signal, good ground, alternating signal as the engine is cranked over. I'd say the sensor is functioning properly. My crank sensor is a new Mopar unit as of a few months ago.

Anyone have similar experiences with this?

My similar experience had more to do with a bad check valve in the fuel line. Next time you start the Jeep, cycle the key from off to run, wait 20 seconds and repeat one or two more times before cranking. If the engine fires right up, the check valve is letting fuel pressure at the rail drop.

Forgot to mention, I have tried the poor man's prime. Also checked fuel pressure with gauge, correct when running and it does not bleed down. Thanks though!

Years ago I had the same symptoms with my '93 XJ, too. I threw in a new MOPAR CPS,
NGK spark plugs, distributor cap and rotor at it, all without change. Fuel pressure was OK.
Turned out to be a bad MAP sensor. Test yours before blindly throwing new parts at it.

Save us time here, What have you already tested and verified and replaced? Does it spark on the first crank or take 3-4 seconds to start sparking on the primary wire?

Here are the results from my diagnosis:

MAP Sensor Test:

0 in-Hg = 4.7V
5 in-Hg = 3.9V
10 in-Hg = 3.0V
20 in-Hg = 1.280V (This is the only one that differs from the book value of 1.1V)

The sensor holds 20 in-Hg of vacuum for a long time. I checked for 5V reference signal, and the ground is good. The signal wire to PCM has good continuity.

TPS Sensor Test:

Idle 0.752V
WOT 3.608V

Then I performed a sweep with an analog meter and tapped on it while advancing through the throttle. The sweep is clean with no dips or dead spots. 5V reference signal, and ground are good. The signal wire to PCM has good continuity.

Fuel Pressure Test:

Fuel pump prime (Ign to ON) = 35 PSI
Engine Idle = 33 PSI
Vacuum removed = 42PSI

Fuel pressure regulator holds 20 in-Hg of vacuum for a long time. The fuel pressure dropped from 31 psi with the engine off to 25 psi after an hour, but held 10psi until the following morning.

O2 Sensor
I checked the heater circuit and got 7Ohms, which is good. I don't have a scope to verify the waveform though.

IAT and CTS
I have checked these sensors multiple times at different temperatures and they always read in the correct range according to FSM. I also removed the IAT and checked more temperature ranges by exposing it to cold and hot air. These appear to be good.


I'm going to check what you said Mike if it sparks right away or after a few cranks. I replaced the CPS with a Mopar unit about 6 months ago because the engine was cutting out on the highway for a few seconds at a time.

Is the transmission manual or automatic?

Thanks for the great details, it helps a lot!!!

I had similar issue, my 99 took a few seconds to start and stumbled after freeway driving (376k miles, original everything). Changed out fuel injectors, that seems to have fixed startup and rough running after fwy drive.
Im not sure how to diagnose injector issues, my fault diagnoses was realy a guess. I didnt check fuel rail pressure as you have done. Im just offering what worked for me

It's an automatic Mike.

SleeperXJ said:

I had similar issue, my 99 took a few seconds to start and stumbled after freeway driving (376k miles, original everything). Changed out fuel injectors, that seems to have fixed startup and rough running after fwy drive.
I'm not sure how to diagnose injector issues, my fault diagnoses was really a guess. I didn't check fuel rail pressure as you have done. I'm just offering what worked for me

Click to expand...

I have leak tested mine unmounted using a 9 volt battery to see if they open and if they leak by blowing into the inlet. They can be leak tested by pulling the rack, injectors still attached with the safety clips holding the injectors to the loose fuel rail, then turn the ignition to run only, DO NOT START!! There is also a low cost Noid light (flashing LED) you can buy on ebay that you can attach to one injector wire at a time to see if the ECU/PCM is getting a firing signal to the connector while the engine is running on 5 others. If you can rig up a test fixture to feed fuel to one injector at a time you can check the spray pattern using a 9 volt battery to open one.

These sound a little low to me, any one have the FSM specs handy for his 93?

TPS Sensor Test:

Idle 0.752V
WOT 3.608V

Mike, I thought the same thing but remembered that I had written down my TPS numbers before I had this issue. They are pretty much the same within a few mV.

In the FSM, the first section says "This will vary in an approximate range of from 1 volt at minimum throttle opening (idle), to 4 volts at wide open throttle."

In the testing section it says "At idle, TPS output voltage should must be greater than 200 millivolts. At wide open throttle, TPS output voltage must be less than 4.8 volts. The output voltage should increase gradually as the throttle plate is slowly opened from idle to WOT."

It would seem the TPS is OK according to FSM?

I agree, sounds the HO XJ's have a lot room for slop in the TPS values. The 87-90 Renix (all mine are Renix) is very picky!!! A .10 volt change in the idle TPS value results in a huge change in the idle speed, like +/- and extra 500 rpm.

Mine started doing the same thing after my trip down to Louisville for the Uimited Off Riad expo. 2 hour drive each way. .. I think I'll start with checking the MAP. I've replaced my injectors year ago in a month with EV6s.(7/3/15) Then check out the cps.

Thank you so much for starting this thread so I didn't have to ha

TPS. Not cps.. My bad

I should mention that it seems to start much faster when warm. That was what initially made me think of the coolant temp sensor or intake air temp, but those check out OK.

Any more thoughts?