87 4.0, long-cranking hard start when hot, acts like flooded carb - solved

[87MJJeep]

I have experienced for a while the long crank time, when my 4.0 has sat anywhere from 30 minutes to 6-7 hrs.  But stone (overnight) cold, it fires up as it's supposed to with just a few spins.  When it would have the long crank times, once it did start, I usually smelled gas in the exhaust.  Just like the engine was getting flooded.  I found this thread on a Jeep site from 2011:

 

87 Cherokee 4.0L - hard to start when hot | Jeep Enthusiast Forums

 

Eerily the same issue.  That Cherokee owner replaced all sorts of parts, but he finally determined it to be the fuel pressure regulator (post #8).  All last week, I pulled the vacuum line off the regulator when I arrived at work.  When it was time to go home, it started up just fine.  Two days I could smell gas when I walked up to it to leave.  One time I disconnected the line from the intake and left it on the regulator.  There was gasoline residue on the end of the hose fitting where it had burped fuel far enough to the other end of the line.  

 

What's odd is it doesn't leak immediately after shutting down.  The regulator's internal leak must be slow. 

 

Of course, my replacement FPR leaks *externally* hence my other thread...

 

I'm back to pulling my vacuum line each time I park it.  

Edited October 3, 2022 by 87MJJeep

[Ωhm]

50 minutes ago, 87MJJeep said:

I'm back to pulling my vacuum line each time I park it.  

 

Try this instead of pulling the vacuum line off each time, until you get your new FPR. During CRANK hold the throttle pedal at WOT. This creates a CLEAR FLOOD condition and shuts off the injectors between the cranking speeds of 300-400 RPMs. May help here.

[87MJJeep]

1 hour ago, Ωhm said:

 

Try this instead of pulling the vacuum line off each time, until you get your new FPR. During CRANK hold the throttle pedal at WOT. This creates a CLEAR FLOOD condition and shuts off the injectors between the cranking speeds of 300-400 RPMs. May help here.

Thank you!  I wondered if there was a built-in way to clear a flood like the carb days!  

[gogmorgo]

Even if there wasn’t a clear-flood mode at WOT, simply opening the throttle to allow more air in will help blow the excess fuel through and lean out the mixture. It’s part of what helps clear out a flooded carb.

I’ve had a few injected vehicles where I’ve had to give them 1/4 throttle or so to start in extreme cold. They’ll sit there and crank and not start, but crack the throttle and they fire right up. Probably some issue with temp sensors or the IAC that only presents at -30, I never bothered digging into it. Once they start they’ll be fine until they cold soak overnight. 

[87MJJeep]

That makes good sense!  

 

I got another new FPR last night, so all is well now.  

 

I wish I had gotten fed up with the long cranking sooner for the starter and battery's sake.  At least I got it solved now the temps are dropping, and the oil will be maxing out the 15 in 15W-40.  I noticed it was cranking a little slower this past week.