Hello everyone.
I’m posting here for the first time, but I visit the forum very often, love reading different tips, opinions and for me it’s been extremely helpful. I love this forum and the entire Jeep community.

I am the owner of 1990 Jeep Wagoneer Limited (Renix 4.0l, 136kW, 4x4, AW4, NP242) with 162k miles on it. I bought it five years ago with around 130k miles on it. It’s pretty much stock, no lift, huge tires, or any other mods, other than it’s converted to LPG, since it’s my daily driver and it’s much cheaper here in Europe. It’s well maintained, no rust, no saggy rear end, overheating issues, leaks or any major problems. It had a couple of electrical problems in the past, which is normal for the Renix era, but I managed to fix all of them. I’m very thankful for cruiser54’s tips, I’ve done a lot of those and they made a huge difference. Other than that, Jeep starts and runs like a champ and it’s very reliable. I use it for city and highway driving and some light off-roading from time to time.

But, this is my issue and it started around 2-3 months ago. When I start it, it drives fine, but after around 15 mins of city driving and with operating temp, the RPMs start to drop down and it gets excessive when I come to stop. It feels like it’s going to shut off and then it gets back to normal. It gets worse when I drive in reverse slowly and a few weeks ago it shut off completely while driving in R and stopping. I started it and it worked good. Also, while driving 10-30 mph, it sometimes feel like it loses power for a second or two and then it gets back to normal. This never happens on highway speeds, where I usually go 50-80 mph. This only happens with petrol, not with LPG, and happens regardless of the outside temp, whether it’s cold or warm.

I recently replaced: oil and filter, trans oil and filter, new coolant and flush, fuel pump, fuel filter and air filter. About a year ago I replaced all the other fluids (transfer case, front and rear diff, power stearing), all breaks are new, all grounds are refreshed and I added a couple of new ones, and I also replaced a valve cover gasket. About two years ago, I replaced fuel injectors, vacuum lines, ignition coil, distributor cap, spark plugs and wires. There’s probably more that I can’t remember now. 😊

As for my issue, I tried with different CPS, TPS, MAPs, fuel pumps (Bosch fuel pump, Carter Fuel pump and assembly) and I cleaned the TB and IAC thoroughly. I also cleaned the gas tank but never used a sea foam. I’m not sure if my problem is air or fuel related or it’s something electrical, from what I read it very well might be the heat soak. I never replaced my O2 sensor, so I’m leaning towards that as well.

Thank you so much for your help, I appreciate your opinions.

Cheers!

 

go to www.cruiser54.com and complete Tips 1,3,4, and 5 to begin with.
Clean the throttle body. Tip 11

Make sure your intake manifold fasteners are not loose.

How long since new plugs, wires, cap and rotor?

 

Hey cruiser54. Thanks for your reply.
I already completed 1, 3 and 4 tips. I also completed tips 7, 8, 9, 11, 18, 28, 29 and I plan on working on other ones in future too. They’ve been of great help and the performance of my Jeep is noticable.
Some of the tips I complete at least once a year. I haven’t done tip 5 yet, I’ll probably do it later today. I cleaned the TB and IAC ten days ago and put a new gasket for the TB.
As for the intake manifold bolts, I haven’t checked them yet, but it’s a good call since I replaced the intake manifold gasket a year ago and it was done by my mechanic, so I assume the bolts might have loosen up by the time. I will check that later today as well.
The plugs, wires, cap and rotor have been replaced two years ago.
Cheers!

 

You're off to a good start!!

 

Thank you sir! I'm working on the intake manifold bolts at the moment, but this LPG installation is giving me headaches.
I'll probably need a help from my mechanic and his toolbox.

 

take the airbox out and go under the manifold.
Propane, huh? What spark plugs are you using and what's the gap?

 

Yes, that’s what I’m planning to do tomorrow with my mechanic since he has much more skills than I do.
I use NGK 7938 V-Power spark plugs with the 0.036" gap, been using them for two years now and I’m very happy with how they work, no issues whatsoever.
The propane kit I use is Lovato, with Tomasetto reducer and 20 gallon tank. It’s been working great as well, no difference from petrol when it comes to power and performance.
I’ve been using it for 5 years now and my wallet is also happy with it 😊

 

The intake manifold bolts are all tight, nothing loose there. I also checked the fuel pressure, and it reads 48 psi with engine running.
The problem persists and it's more noticeable if I drive, make a short stop (10-15 mins) and then start it and drive again.
I lean towards the heat soak, I will also try with the O2 sensor if I find one to replace in the couple of next days.

 

Heat soak was never really an issue with Renix.

 

Hmm, didn't know that. I will check the fuel lines tomorrow as well, I'm not sure if the issue could be fuel pump related, I tested Carter fuel pump and assembly and Bosch fuel pump, worked the same like with my old fuel pump.