Long Crank / Labored Start

Hey all,


I've been lurking a lot of helpful threads for a few weeks now trying to diagnose the long crank and hard starting my 1996 Cherokee XJ. I'm running out of things to test so I figured I'd make a thread.



My Jeep cranks for around 5-10 long seconds and then stumbles to a start only after repeatedly and aggressively blipping the throttle to bring the RPMs up. At first while cranking there's no RPM change but as the truck stumbles, blipping the throttle clearly brings the tach up.



When the truck has warmed up it hard starts almost immediately but still stumbles a bit for a second or two before it catches its breath.



Once started my Jeep runs like a top. No coughing/shuddering. Great on the freeway. No change in MPGs.



This weekend I load tested the 3 year old battery and it failed loading twice. It was under warranty so I got a fresh one and put it in this morning--no change in the starting issue.



I tested pressure off of the Schrader valve multiple times both while the truck was running, immediately after turning the truck off, and 15-30 minutes after turning the truck off. All values were nominal at 49 PSI and pressure values remained above 30 PSI even up to an hour after shutoff.



This March I changed both the fuel pump assembly, the fuel filter, the 3/8ths hose from the filter to the tank bulkhead, and the fuel injectors from EV1s to EV4 injectors.


I tested the crank trigger pig tail connector with my multimeter and got the right resistance values from the crank trigger test on the forum here. My crank trigger and coil pickup are only 2 years old and since the truck does eventually start and runs great (no random shutoffs or stalls) I am hesitant to change the sensor on a hunch.



Additionally since the truck does start and run I know I am getting spark eventually and have confirmed I am getting fuel at the rail as noted above.



One last important thing to note is that for around a year now I no longer can get my OBDII scanner tool to communicate with my Jeep. Works with all of my other cars but the Jeep crosses its arms and says "no". I have tried other OBDII scanner tools as well and none them can get a read. This truck was supposedly the first year of OBDII XJ's and OBDII is a backwards compatible communications protocol so I have no idea what this could mean beyond the ECMs OBDII communications port going on the fritz. Could be unrelated but I figured I'd mention it.



I greatly appreciate any suggestions, guesses, or any form of further insight.



Thanks!

-Wyvern

What brand is the crank position sensor? Many folks have poor results/short lifetimes from non-OEM units.

On the Dianostic port, maybe there's a disconnected/broken/corroded wire between the port and the ECU? Was anything done to the truck electrically around the time the scanner stopped working with the Jeep?

After much investigation I have figured out my issue, at least partially. I'm posting this here for anyone who was interested and may find this via a search. I had gone through, cleaning my grounds, testing for spark on all 6 of my plug wires with a screwdriver against the block, checking fuel pressure in every scenario imaginable off of the Schrader valve, and even cleaning the injectors. Everything looked good to me but the issue persisted. I have been having a parallel issue in which my jeep starts to overheat in drive thrus after I've been driving for an hour plus. I tracked that down to my electric fan never turning on despite my jeep's temp gauge going up past 230 F. My solution was to turn on the AC (because in my '96 this forces the electric fan on and actually cools down my engine). I decided this weekend to finally replace the coolant temperature sensor the goes to the computer to hopefully get it to turn on the electric fan at the right temperature. As an aside, I know my temperature gauge is accurate as I had replaced the sending unit last Winter. Now with the new coolant sensor in the thermostat housing my jeep starts up cold after about 3 solid seconds of cranking. Once even slightly warm it will start in half a starter turn almost instantly. Seemed strange to me but in addition now the electric fan comes on at about 227 F right where it should and I no longer go past ~ 230 F. I'm sort of mystified why this has mitigated my issue. Three seconds + is still a bit of a long time to crank to me and I'm still unsure why it's only present when cold but the situation is much, much improved and starting is now 100% reliable. Thanks all, -Wyvern

You replaced the CTS in the radiator? Not the one in the block.

No sir, what was replaced was the coolant temperature sensor located in the thermostat housing at the front of the block.
The one in the back of the block toward the firewall is not the sensor that sends data to the PCM, it's the sending unit for the gauge cluster.
Thanks,
-Wyvern

Hm. If the sensor's failure mode resulted in an improbably low temperature reading back to the ECU, it could have been over-enriching the mixture and effectively "flooding" the engine because it thought it was -27F or something similarly absurd.

I'd wager your fuel economy will go up now that you have a good sensor providing proper engine temp data to the ECU...