Hard to start when warm ('88) - fixed

[brucecooner]

If I park my '88 for a while and come back to it while it's still warm to start it back up, it will turn over, but would really prefer not to start. 

 

Some application of the gas pedal, but not too much, will get it to fire up and after that it seems pretty okay.

I'm wondering if the fuel system is getting confused while it's still warm.

 

Cold starts don't have any issues.

 

[EDIT -> THE ANSWER] If you've arrived at this thread after searching for why your 4.0 doesn't like to start when it's warm, I will save you some reading and tell you here that my particular problem was the fuel pressure regulator leaking through the vacuum line into the intake manifold.  Also, I had the idea of turning the key to pressurize the rail, but leaving the engine cold, then trying to start it later, as a way to see if it's truly heat soak or something else.  Good luck!

 

 

 

Edited January 21 by brucecooner
added the source of my problem to top-of-thread

[cruiser54]

Injectors may be leaking fuel into the engine while parked. 

Does your oil smell like gasoline? 

[brucecooner]

I took several good whiffs of the dipstick while it was sitting cold this afternoon.  I detected a faint sweetness to it.

Pulled the filler cap off the valve cover and get the same there.

I can't say for sure 100% it's gas but it seems close.  I don't want to get a false positive on it just hoping I've found the problem though.

 

No idea if these are the original injectors.

[cruiser54]

Original injectors. 

How does the oil feel if you rub it between your fingers? 

[brucecooner]

Dang it, I didn't see your reply in time for my explorations under the hood this afternoon.

I'll check the feel of the oil out next time it's up. 

I seem to remember that good oil has a slight tackiness to it, you should feel it holding your fingers together ever so slightly before they come apart.

 

I drove it to the gas station this evening, then around the countryside a bit.

When I got it back in the driveway and turned the motor off, I waited a few seconds and turned the key again.

I figured restarting it right away, before fuel has time to drain out of the rail, might be a good test of your theory.

It started right up, no hesitation and no help needed.

 

So it's not strictly a warm engine behavior, looks like it has to sit a while before you get the difficult start.

 

[cruiser54]

You're on to something.....

[brucecooner]

Okay, I pulled the dipstick and took a look.

 

It...looks like oil.  Clearly changed recently.

I got some between my fingers and it does not feel "liquidy" at all, not like lighter weight fluids.

It is definitely forming a coating between my fingers that keeps them apart as I glide my fingertips over each other.
It is slightly tacky when I pry them apart.

 

As far as I can tell, the oil feels normal.

 

The oil pressure according to the gauge goes from upper 20's at idle to 40 on the nose on the highway.

Maybe not as high as I've heard but seems within operating ranges. 

Not sure if that would be a reliable indicator of fouling oil anyway.

 

When it's being hard to start, a mild pump on the accelerator helps.

Sometimes I'll smell gas after it starts, like maybe I overdid it.

But would needing a shot of fuel indicate some other issue?

 

 

 

[cruiser54]

So, all we need to be concerned about is the hard start after being parked for a while.

[brucecooner]

44 minutes ago, cruiser54 said:

So, all we need to be concerned about is the hard start after being parked for a while.

Yes sir!

 

Other than that slow start it actually runs very nice.

 

Well, it's got that weird surging idle.

And it needs a new valve cover gasket, and other normal old Jeep stuff.

But overall it seems to be doing well for a 30+ year old vehicle.

 

 

[cruiser54]

Ok, surging idle and hard start after being parked for a while when warm? 

Which of my first five Tips have you completed? 

[brucecooner]

On 5/15/2022 at 10:30 PM, cruiser54 said:

Ok, surging idle and hard start after being parked for a while when warm? 

Which of my first five Tips have you completed? 

Between work and weather (Phoenix summers!) and other obligations I've had little time to raise the hood.

 

I did have a small win today. The interior lights weren't coming on, but with a multimeter and some fiddling about, I learned that I don't know how to work a light switch (or read a user's manual, I guess).

 

I've acquired some OxGard though (I shopped around to make sure I get OX-100-B instead of OX-400-B, which probably makes no difference but your site showed a picture of OX-100-B, and I'm a stickler when it comes to following instructions), so cleaning some grounds is up next on my list, soon as I spray the grime off the passenger side of the block.

 

Regarding that idle irregularity, should I be suspicious of the Idle Air Control thingy on the throttle body?

 

 

[cruiser54]

Not yet. get those Tips done first. Then you'll know grounds or faulty connections are not the root cause. 

[brucecooner]

I actually found time to do the first tip this evening, the major grounds near the dipstick.  I also went after the other end of the line that goes from that stud to the inner fender.

https://comancheclub.com/topic/68912-bruce-has-to-enroll-at-mj-academy/?do=findComment&comment=723322

 

Afterward I got in it and started it to make sure I hadn't bricked it, and once it idled down it seemed the dips in the RPM were going lower than they did before.

The RPM would even dip low enough to seem like it was going to stall, which it hasn't been doing.

I've also noted that if I blip the throttle, when it comes down it'll do the really low RPM thing and act like it wants to stall then too. 

May be related, may not be.

 

I was just fiddling around on the passenger side of the block tonight, but is it possible I knocked something else loose, or maybe I bumped a hose and made the leak worse?

 

 

 

[brucecooner]

Been a while since I've had the time or health to fiddle with the Jeep, but it's still giving me the hard start when warm.

I'll drive it for short hops where I know I can jump back in it right away, but if I part it at a store or anywhere for a while, sometimes it will darn near not want to start.

 

I got a fuel pressure gauge for the rail recently to see if it really is the fuel pump, and I think I've ruled out a fuel issue.

 

At a cold start the rail goes right up to 30-ish pounds as soon as you turn the key.

I drove it a couple dozen miles the other day and parked it in the driveway. Immediately put on the gauge and it pressurized soon as soon as the key was on.

It started right away.

I went out maybe ten minutes or so later, and again it pressurized and started pretty quick.

I went out about twenty or thirty minutes later, and although the pump was still pressurizing the rail, it would crank but didn't want to start.

So I don't think it's anything with fuel delivery, maybe something with spark.

 

Is it a useful clue that it has to sit for a while before I get the hard start?

I would have thought after a long drive everything would be good and hot, but it had to sit there a while before the hard start.

 

I have noticed that right after it does have a sluggish start, it misses a few times before settling in, so maybe spark is the issue.

I would think I could rule out the distributor, being right next to the engine it's surely good and hot all the time.

 

Anyway, has anyone ever seen a Renix that has to sit up a while to get heat soaked?

 

That would seem to point to something farther away from the engine, I think.

 

I've done the grounds on the block and the block to firewall (a previous own actually installed two ground straps to the firewall).

I guess I need to do the C101 delete.

[Ωhm]

On 5/16/2022 at 12:40 AM, brucecooner said:

When it's being hard to start, a mild pump on the accelerator helps.

Sometimes I'll smell gas after it starts, like maybe I overdid it.

But would needing a shot of fuel indicate some other issue?

 

Try holding throttle plate at the WOT position. During CRANK this will shut-off the fuel injectors (clear flood) until engine speed reaches 400rpms. Looking for slow leaky injector(s). Does this cut down on CRANK time when engine is HOT SOAKED?

[brucecooner]

6 hours ago, Ωhm said:

 

Try holding throttle plate at the WOT position. During CRANK this will shut-off the fuel injectors (clear flood) until engine speed reaches 400rpms. Looking for slow leaky injector(s). Does this cut down on CRANK time when engine is HOT SOAKED?

I did suspect leaky injectors when I first started looking into this, and replaced the originals with a set of rebuilt 4-hole injectors.  The old ones were very dirty.

I will try the WOT trick next time I'm messing with it though.

 

I have one of the lights that you put in a plug wire to check for spark, I need to dig it out and start checking that all the cylinders are firing.

 

[Ωhm]

One more quick check. Look at the vacuum hose for fuel between the Fuel Pressure Regulator (FPR) and intake manifold. Another chance for a slow fuel leak.

[TurboedMJ]

I am also having issues with the surging idle. I know it's not: fuel pump, filter or injectors. I am going to rent a fuel pressure testing kit and see if that changes when the idle dips. Please update this thread if you happen to fix the surging idle. 

[brucecooner]

On 1/2/2024 at 5:50 PM, TurboedMJ said:

I am also having issues with the surging idle. I know it's not: fuel pump, filter or injectors. I am going to rent a fuel pressure testing kit and see if that changes when the idle dips. Please update this thread if you happen to fix the surging idle. 

 

I'll definitely make an update if I learn anything about the idle.

 

On 12/28/2023 at 1:12 PM, Ωhm said:

One more quick check. Look at the vacuum hose for fuel between the Fuel Pressure Regulator (FPR) and intake manifold. Another chance for a slow fuel leak.

 

Today I finally got a chance to debug the Jeep again. 

I've searched a lot of threads on hard crank, and the only one I've found that matches my motor and situation exactly was due to leaky injectors.

 

I trust the source of my rebuilt injectors, but he could have just rebuilt a set with some worn out ones that leak.

However, if it's leaky injectors, I had the revelation that I can just REMOVE heat from the equation.

So I turned the key and pressurized the rail, then turned the key off and walked away.

In about half an hour it started, pretty much okay but a little slower than a cold start.

This start re-pressurized the rail, so I gave it another half hour or so.

The next start took several revolutions, and it ran rough for a few revolutions after.

Mind you, it was a cool day and the engine is in the shade of the hood, everything was cool to the touch all day.

This is NOT a heat soak situation.

Another half hour, another start, and it was getting really difficult.

My son watched was behind it and said the tailpipe was putting out some white smoke.  Hmm....

I waited again and had my son start it while I watched the tailpipe, and it was giving off a good bit of white smoke.

 

So I was all ready to blame the injectors, BUT I remembered Ohm's note about the FPR.

I pulled the line from the regulator to the intake manifold and gas came out.

I'm pretty sure it's not supposed to do that, is it?

 

So at this point I'm pretty suspicious of the regulator.

With that line pulled, the rail was still holding pressure, mostly.  It does do down slowly over about 10 minutes or so.

I had to button everything up at this point, but since then I've had the thought I should pressurize the rail and then pull the FPR line so that it CAN'T leak

back into the intake manifold, and see if that changes my result.  Then I should know it's the FPR for sure. 

At any rate, it seems to need a new regulator for sure.

 

 

 

 

 

 

[Ωhm]

14 hours ago, brucecooner said:

I'm pretty sure it's not supposed to do that, is it?

 

Leaky FPR is like having a 7th injector. Once replaced a short period of idle/driving time is needed for the ECU Fuel Trims (STFT/LTFT) to find themselves again. Keep us posted.

[cruiser54]

So, fuel is leaking at the vacuum line and not one of the other fittings on the fuel pressure regulator?

 

 

[Ωhm]

18 minutes ago, cruiser54 said:

So, fuel is leaking at the vacuum line and not one of the other fittings on the fuel pressure regulator?

 

 

14 hours ago, brucecooner said:

I pulled the line from the regulator to the intake manifold and gas came out.

I'm pretty sure it's not supposed to do that, is it?

 

Too me it did look like the vacuum line.

[cruiser54]

My bad. I had this thread confused with another one. 

[brucecooner]

It took me long enough (life's been crazy lately) but I can finally report that a new fuel pressure regulator seems to have fixed the problem.

 

I put a new unit on about three weeks ago, but didn't have the chance to really get out in the Jeep until this weekend.

Whenever I got in it yesterday and turned the key, it would start.

It doesn't start fast, it takes it a few turns to get going, but based on all the videos I've watched where somebody starts an old 4.0 that's par for the course.

Apparently deleting my "7th injector" was the cure.

 

Warning to anyone undertaking this, the new unit's vacuum line input might be a different size than the old elbow.  I just cut a short length of quarter inch silicone tube I had lying around and that made for a snug fit.

Also, the little nuts and bolts (T25) that hold the regulator's bracket to the rail are not the easiest to get to.

I removed that bracket to the right that carries the CCV tube (and others), and disconnected injector #1 and moved everything back as far as I could and it was still a finger ballet to get the little bolts back in the bracket.  I highly recommend putting tape or paper towels under the regulator area or else you will lose bits to the depths (there's a T25 bit that lives somewhere under my intake manifold now).

 

So a big huge thanks to Omega-hm (how does he type that?) for pointing me to the FPR

On 12/28/2023 at 1:12 PM, Ωhm said:

One more quick check. Look at the vacuum hose for fuel between the Fuel Pressure Regulator (FPR) and intake manifold. Another chance for a slow fuel leak.

 

 

And thanks to everyone else who's been along on this thread.

 

 

On 1/2/2024 at 5:50 PM, TurboedMJ said:

I am also having issues with the surging idle. I know it's not: fuel pump, filter or injectors. I am going to rent a fuel pressure testing kit and see if that changes when the idle dips. Please update this thread if you happen to fix the surging idle. 

I am sorry to say that this did NOT fix the surging idle.

I'll have to continue on with cruiser's tips.

 

Of course I was immediately punished for fixing this issue with the development of a fat new oil seep, coming down the passenger side of the pan from...somewhere. I snugged a few pan bolts but that wasn't it.

But I didn't name this thing the Heartbreaker for nothing lol.

 

 

 

 

 

[fiatslug87]

Congrats, but it’s always something with these old engines. Check the oil filter mount for leakage, takes three o-rings.