AZjeepin1

Recently my XJ has been having difficulty starting on the initial crank. Before, it used to start up very sharply, but now I have to pump the gas pedal in order to get it to start. And when it finally starts, it stumbles into a start as opposed to firing right up.

Nothing has changed from then to now. What I need to know is what sensors should I be looking at as a culprit? Or could this be something worse like the cam rounding itself off?

mr white

How old is your battery?

Agent_Oragnge

Year and Drive Train please. remember, start simple. you're curing the headache by cutting off the head.

Baby D

year? drive train? have you done any work to it lately? do all ur gauges work correctly? like oil pressure, coolant temp etc.? hve you checked all fuses? after fuses have you checked relay? when was the last time you replaced fuel filter? is your check engine light on? give us more info plz.

AZjeepin1

My apologies...

'88 4.6l/AW4/NP231
No recent work on the motor minus a new IAC valve (2 months ago)
Battery is only 2 months old (Optima Yellow Top)
Gauges are all functional and show normal readings.
Fuel filter is about a year and a half old, but only has ~3k miles on it
No check engine light
Fuses are all good to go

AZjeepin1

No ideas??

tjwalker

Having to "tip in" the throttle to start the engine can be a symptom of a bad throttle position sensor. I'd test it.

AZjeepin1

TPS is fairly new (within 3k miles) but I'll check it and keep you posted!

Would running rich also produce these symptoms? I have an adjustable FPR on my Jeep, so maybe that went bad??

cruiser54

Do this:

And read and perform the #s 2, 3, and 4 in the link in my signature.


Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
If you want to upgrade your grounds and battery cables in general, contact Jon at


www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 03-04-2013

Click-Click-Pull

Admit...not very familar with the Renix. However I would suggest the see if the fuel pressure is holding after shutting off ignition and pressure before cold start. Trying the poor mans prime...?
My .02

AZjeepin1

TPS was a little off, so got that adjusted...

Followed cruiser's #2,3, and 4 tips...

Fuel pressure is good...

STILL having the issue. Anymore ideas?

AZjeepin1

Coolant temp sensor maybe? Only has about 3k miles on it but is 2 years old... Not sure how to test it either.

cruiser54

How are you checking fuel pressure?

The hose/piping from the throttle body to the MAP sensor on the firewall can have NO leaks. If it does, the MAP thinks the engine vacuum is low and signals the eCU to richen the mixture.

Have you done the sensor ground test? #5.

AZjeepin1

I'm checking fuel pressure via a rail-mounted gauge (mounted where the schrader valve is)

MAP vacuum is solid, no leaks or holes.

I've done #5 and I'm in the clear. When I did my motor swap ~3k miles ago I livened up all the grounds and used larger grounding cables as well...

cruiser54

Try this for giggles. Remove your IAT. Carefully clean the tip of it with brake cleaner or throttle body cleaner. I noticed over a 10% difference in resistance between clean and dirty.