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As soon as I thought that repairs had come to an end - new problem emerges. I was driving my Jeep and suddenly I started to hear repeating clicks, something similar to sonar sounds. I've stopped and thought that I've heard one of the pulleys, but while I was looking at car it just died. And haven't started since. It throws code 54 - distributor sync pick up, so I replaced that part with another one from XJ - and got same code again. I doubt both parts are bad. I have fuel at rail but no spark at ignition coil. My friend - mechanic, told me that maybe ignition coil is bad. Could this happen? My biggest fear is that something is wrong with PCM, but I can easily hook it to Snap On diagnostic scanner and read everything.. And there it says - cam sensor-NO. Should PCM block both fuel and spark and not only spark if it doesn't have signal from Crankshaft or Camshaft position sensor?

Gauge is inaccurate, but I'm not sure yet if it is something wrong with a gauge or with sending unit. I can't see how gauge can fail. Yet, temp sending unit Ohm readings are just as they should be. Seems that my old stock thermostat (that probably came with a vehicle from factory) was bad and was opening late or not opening completely, and since gauge shows smaller readings than real, that confused me because even though engine was running a bit hot gauge needle was just where it should be. New thermostat I bought from Crown was opening a bit soon, so engine wouldn't reach recommended operating temp (195f). I took Motorcraft fail-safe 195F thermostat, and even though I still have inaccurate gauge readings, engine warms up to operating temp. I know this because I hooked PCM to Snap On MT2500 and CTS reads 90-91 degrees Celsius (equals to 195F), while gauge reads about 176F. I will try first with new sending unit, and if that doesn't help, then the gauge is to blame.

Well, it is definitely stretched a bit and slaps when cold (its pretty silent when warm). I will replace it however very soon. For now, idling is much smoother than before, but I guess that it'd be even better with chain being replaced.

Timing chain is also a bit stretched so it probably slaps a bit but it still doesn't need replacement.

Finally found a solution to this problem - lifters at #3 and #5 cylinders were bad. I've replaced all 12 of them and no more ticking. Should I have replaced timing chain and camshaft?

Well, in the end, there was some play at pitman arm, so I've replaced it with a new one and now there is almost no movement.

I'm aware that thermostat is completely mechanical device. I tested resistance on CTS and temperature sending unit (that little one at the back of the engine) for another reason - if they both read similar temperature - then probably its thermostat problem because its not that likely that they both failed at the same time. From ohm readings I got, they both read around 87-88 degrees celsius so I guess its inaccurate temp gauge that is giving me problems. Anyway, I will try with another new thermostat and check if there are improvements. If not then I guess its inaccurate temp gauge or bad temperature sending unit. As for the water pump, I checked impeller orientation. They are both in same direction, even the water pump I have removed had stamped "R" mark on impeller and housing. Part number shows that this water pump fits both XJ but with 2.5 engine and YJ from 1991 to 1995 with 2.5 or 4.0.

I tested resistance from CTS and temp sending unit - CTS: 1008 ohm steady (guess when tstat is steadily opened, it goes lower and then higher until it finally reaches 1008 ohms) TSU: 272-275 ohm depends where second probe is grounded From some resistance tables I've found on the internet, 1008 is somewhere between 80 and 90 C (175 and 194 F). Would this be normal even if tstat is rated at 195F? For TSU I have only found some tables but they don't say that its for temperature sending unit. 270 ohm would be around 87-88 C. All the time temp gauge shows around 70-75 C, it reads lower.

Thank you Moses. Right now I have opposite problem. I've put in new brand new thermostat today, 195F rated. Everything is in place as it should be and now water temp won't rise above first quarter mark (that is about 70C deg). I think it's not stuck open because water is cold inside radiator until temp rise to that mark. I know there is CTS in tstat housing, and another sending unit in the back of the engine - but I'm not sure if they are to blame because i used to get higher readings with old thermostat in it. Old tstat is stock, seems like it was never replaced before.

Hello all! I've recently replaced my water pump, and I was wondering what is normal operating temperature range on 4.0L Jeeps? I have celsius temp gauge, and most of the time it's one line below half ( it's around 85 degrees celsius~=185F. I have 195F tstat in Jeep. When I'm on 7-10% incline, temp would rise near half mark- 100C (210F). Jeep has 32rh automatic with 33 inch tires. Before I installed those tires temp would always stay near that 185 mark - one line below half mark. Water pump, tstat, radiator - all new. Air burped out of cooling system. Only thing that comes to my mind is strain from bigger tires and fact that now engine runs on lower rpms than before, which makes water pump and fan turn slower.

Hello, I was recently replacing water pump and because I had to wait for Jeep to idle and burp air out of cooling system I've noticed some things: The ticking I've described doesn't begin immediately after engine starts. When I first noticed this I thought that it happens because engine starts on a bit higher rpm and that is why it could not be heard. But later I realized that it corresponds to oil pressure - as soon as oil pressure rises to maximum ( it never goes past 60-65 psi) the ticking fades in. I've tested this on warm day when revs would drop to 800 rpm soon, and there was no ticking (or it was too silent to be detectable) until oil pressure got to maximum. I left my Jeep idle to burp any air from cooling system, and even engine got to operating temp and idled for 20 minutes, ticking wasn't gone. But after driving it for a minute or so, oil pressure was a bit under 40 psi and there was no more ticking. Would those two things be the symptoms of piston slap? I guess that slapping would start as soon as engine starts (or at least drops down rpm).

There is some play in steering wheel (precisely in steering gear box) and I have power steering. Its saginaw unit, and I've found that it has some adjusting screw on top of it and that by adjusting that screw I can reduce play. On the other hand, I've read that this should be done only after rebuilding complete unit and that adjusting it without rebuild could make elements inside bind and damage the unit. Can it be done or I need to rebuild it first? It has some 180.000 miles on it and no visible leaks on it nor on ps pump.

Thank you a lot. I was unable to detect anything by removing spark plug cables. Maybe I have more than one slapping piston. I guess that I will drop oil pan on next oil change, and check for loose pistons. If I don't find any I will proceed with valvetrain troubleshooting. I'll be back here with the results.

I was unable to pinpoint which cylinder could be the culprit but I've found the video of exactly the same sound. This is an 4.0L cherokee, but on 1:51 when he gets underneath oil pan, its that same hammering sound. This car has also exhaust leak but there is that one hammering sound that can be best heard underneath, like in my situation.

Thank you for extensive response. Here is some kind of history of this engine: I've bought this Jeep with rod knock, so crankshaft and rod bearings were replaced. No more rod knock. Compression was checked - it was in the upper factory range After some time engine developed random tick (it would start randomly at idle and disappear randomly - sounded like it comes from distributor) and it sounded lot more metallic than this knock. But this occurred rarely so i guess that this could be random lifter tick Engine got hydrolocked, and piston connecting rod was replaced. Compression was checked after replacement - it was in the upper factory range. I'm not sure if knock developed immediately after hydrolock or after replacing piston. But since then it is there every time on cold start and it disappears after warm up. As far as I understood, there are two options after I detect origin cylinder of this knock: If it is wrist pin, i should check cylinder walls and if there is no damage - only that piston should be replaced without boring anything? If it is cylinder core shift, engine block should be bored and all piston rings replaced with adequate size? Because of compression test results I guess that rings are not worn on pistons.

Hello all, Three years ago my engine got hydrolocked. After that I replaced piston on cylinder no. 6, because connecting rod was bent a bit. Even after that, there is some knock while engine is cold, that lasts about 2 minutes when engine is cold. After warm up knock is gone. In three years things were not getting worse, even knock is still there. I can't detect knock origin for sure, it sounds like its on the side of the engine where the distributor is, but I can't be sure if it is in the upper or lower part of the engine. After 1300-1400 rpm even when its cold its very hard to detect (but I'm not sure if it is not masked by the engine or fan noise). Last time I checked compression it was in upper factory range. Rod bearings and crankshaft were replaced year before hydrolock. I always thought that this is valve related because lower part of the engine appeared fine, but I've recently heard about piston slap in 4.0 engines. I guess that piston skirt is not broken since noise disappears after warm up. My questions are: 1. How can I detect what is causing this noise without disassembling engine? I've read that if I remove spark plug wire from cylinder and listen for knock, if it gets quieter then its piston slap, if not then rod bearings or valves 2. If it is piston slap, will it do any damage to cylinder walls? Do I need to replace anything else than entire piston?

No, there is no block heater, I drive on gasoline until engine gets to 90-100 deg Fahrenheit. I found that info on internet about 1-2% percent power loss. The thing is that I had both vacuum and sequential, I had much worse mpg and noticeable power loss on vacuum system. I don't feel any difference between driving on propane or petrol now with sequential system (except from the wallet thickness and tailpipe smell ). The only info that Stag ECU gets from Jeeps PCM is that of petrol injector timing. There is no separate distributor for LPG here. Distributor is the same distributor used when running on petrol. I'm not sure, but I think that Stag ECU relays on Jeeps PCM for timing (PCM controls timing from it's own sensors). I think that only thing that LPG ECU controls is air to fuel ratio for propane, based on it's own map, O2,map sensor signal and injector timing that it reads from Jeeps PCM. But I think that there are systems that read crankshaft,camshaft etc sensor data from OBD and then they control ignition timing on their own. You can say that they are like valves. Pressure is reduced primary inside reducer, after that there is pressure in hoses that go from reducer to injectors. As far as I know, there is no pressure boost after injectors, the propane is then sucked in by vacuum I guess.

Well, my Jeep has 130000 miles on odometer and I guess it was mostly driven on LPG here. Main reasons LPG is popular here is that its price is lower than that of gasoline (lowest octane rating for gasoline in my country is 95 octane and its price is 1.32$ per liter -approx 5$ per gallon). LPG costs around 0.60$ per liter so it's around twice cheaper. But there is one problem - engine consumes more propane than petrol (in some cases it can go to 30% more than on petrol). But this depends on a lot of factors: what is the type of the system, was it installed professionally, quality of propane injection map etc. Tailpipe is a lot cleaner, lot less emissions... It's popular mostly in Eastern Europe because of its price, but it's also getting popular in the EU because of less emissions, therefore more benefits when doing yearly registration of the vehicle etc. It's pretty expensive to ride american cars in Europe if you don't switch over to LPG. My vehicle was not serviced so often by previous owners so it developed valve tap when its cold and I've already had to change crankshaft and bearings. But I bought it knowing this and knowing that oil in it was more like a grease than lubricant, so I can't attribute this to LPG. But I guess that I can attribute to it that when I did compression test, I got results like it just came from factory. Cylinder walls, pistons, rings, everything is like it has 130 miles on it instead of 130000. Now about systems, there are two types commonly used here: sequential and vacuum operated(we call it venturi here). Both of them enable the driver to select if he would like to drive on LPG or on petrol, they are dual systems. In each system it is recommended to drive on petrol until engine (and therefore reducer) gets to 40-50 ℃ operating temperature before switching to LPG. 1. In sequential applications it works like multi point injection in petrol vehicles, each cylinder has it's own LPG injector, which is controlled by LPG controller. LPG controller is wired to petrol injectors (so it can read injector times and to cut them off when you turn on LPG). It is also wired to O2 and map sensor so it can control AF ratio. You get LPG in liquid state from tank to reducer. Reducer is connected to LPG filter (with one rubber hose). From LPG filter you get two rubber hoses that conduct propane to groups of injectors ( in my case there are two groups with three injectors in each group). Then on, from each LPG injector goes small diameter rubber hose which is hooked to intake manifold ( manifold is drilled as close as possible to engine head, mostly near where the petrol injectors go into intake manifold). This systems are a bit more expensive than vacuum operated, but they provide much better mpg (comparable to those on petrol) than vacuum operated and you have minimal power loss (1-2%). I'm not sure if this type of system can be installed when petrol injectors are not hooked to intake manifold, or when vehicle doesn't have electronic fuel injection. 2. Vacuum operated (venturi) don't have injectors nor controllers. There is a hose from reducer to mixer (which is installed below throttle body). LPG is sucked in intake manifold by engine vacuum, so propane-air mix is made inside intake manifold. You only need to have switch (which controls when vehicle operate on petrol and when on propane) and emulator for petrol injectors (which cuts them of if you have electronic fuel injection in your vehicle). These systems get less mpg (there were some applications with lambda sensor and one injector but they still get more power loss and worse mpg than sequential systems). Trouble with this system is that detonation could occur inside intake manifold, so it's not recommended for vehicles with plastic intake manifold. Detonations cannot happen in sequential systems. There are some modern applications of sequential systems that read parameters from OBD2 or CAN but I'm not pretty much familiar with them. Now about the classic sequential system: here is the wiring diagram of 4 cylinder version (this type of systems that have no OBD connection or any kind of interface to petrol ECU, everything is wired on directly ). About your questions: Do you have this cooler routed to the A/C system? If so, does the A/C need to run the entire time that the propane fuel is in operation? - Reducer is connected to engines water cooling system. It helps it to reach optimal operating temperature and later on to maintain it. If it was not connected to it it would virtually freeze during operation. I don't have A/C in my Jeep but I guess it doesn't make any difference. Do you have individual (six in this case) port LPG injectors? Is there a separate manifold? I do not see added injectors on the system in the photo. Are they running fuel down the common rail for the OEM gasoline injectors? Using the stock injectors to flow the propane? - Yes, I have individual injectors (six) but there are in 2 groups of 3. Two hoses conduct propane to each group, and from each group you have three small rubber hoses that conduct LPG to intake manifold. There is no separate manifold, OEM manifold is drilled near petrol injector ports. I've marked this on the photo on the bottom of this post. You have OEM injectors for petrol and special injectors for LPG. There is no direct connection between them, but they are both wired to a LPG controller. Do you rely upon the PCM and OEM distributor for spark delivery when running on propane? -Yes. This must be a somewhat popular alternative at Europe if there are apps and this degree of parts available. Was your system specifically designed for the Jeep 4.0L engine? Or did you have a generic system that you have modified to work with your YJ Wrangler's Jeep 4.0L inline six? -This system is generic, made for vehicles with 6 cylinders and electronic fuel injection. I have Stag manufactured system (with some parts from other companies), but I'd strongly recommend Italian made LOVATO kits (here is a link to one of its applications http://www.lovatogas.com/php/eng/lpg_systems_detail/id_39_prodotto_easy-fast-c-obdii-8-cylinders-lpg.html ). I hope that I somehow explained this.. I'd be glad to answer if there are more questions. Regards, Petar.

LPG controller is AC Stag (i think its made in Poland), it's connected to Jeeps O2 and Map sensor. Every cylinder has it's own lpg injector ( its sequential system). This is photo I've found on internet but my installation is similar. You can see that there is a reducer near battery, lpg hoses that go from reducer to injector rails on the right side of the engine. Also, reducer has to be connected to a cooling system. On my car gasoline injectors are wired to a LPG controller (which is not seen here) so that they are shut down when car runs on LPG. As far as I understand, when running on LPG Jeeps PCM send signal to gasoline injectors - and since gasoline injectors are closed that signal is forwarded to a LPG controller so it can calibrate itself (when you perform calibration of the system) and control its own LPG injectors. LPG controller can be accessed by PC with proper cable. I've even found that there are mobile apps that communicate with controller via bluetooth, but you need to have a bluetooth adapter connected to a controller. LPG tank is located in the rear of the vehicle. Those who are interested in this can find more info at: http://www.ac.com.pl/products-autogas/ Driving on LPG should not be more dangerous than on gasoline. LPG tanks are pressurized, but they are made of thick steel and tested on much higher pressures than working pressures (this applies to entire system). Tanks have safety valves in case of increased pressure, traffic accident, that release pressure from tank. Dangers come from installations that are not checked periodically or were installed unprofessionally. LPG can't lit inside tank (like gasoline), but danger comes from leaks that can occur on neglected system components ( like hoses, connectors) and mix with some source of heat.

Do you maybe have exact OTC model that can read live data and dtc's from Jeep OBDI? I've just found Snap-on mt2500 scanner, pretty cheap kit (adapters,cartridges) on e-bay. Seem like it has live data, dtc reader, testing, troubleshooting etc. so I guess I will give it a try. In regard to LPG: after PCM relearn and forms gasoline map, I can connect PC to a LPG controller. There is no interface to Jeeps PCM from LPG controller but there is LPG auto-calibration mode. LPG controller monitors operation of various sensors and fuel injectors in different situations (idle, WOT etc) and form it's own LPG map based on that. As far as I know, LPG controler uses Jeeps O2, MAP and is connected to fuel injectors also. I started having trouble when bad (rich) LPG map was manually loaded so it messed up PCM maps - with long fuel trim (if I remember this property well) being like -80%. In this application Jeep PCM works all the time even when LPG is on, only gasoline injectors don't spray gasoline.

You are certainly more than helpful. I will go through troubleshooting tests and reply here in case that someone else have same troubles. Thank you once again!

Hello, I have some trouble with mpgs, idling and acceleration on my Wrangler YJ 1995. 4.0. Recently went to a mechanic, he connected my PCM to a DRBIII scantool, and he told me that the adaptive factor is -80%. He did reset all adaptive memory, and I can feel improvement in mpg and acceleration. Is there any way to reset adaptive memory other than connecting it to a scantool? I've read on internet about touching positive and negative cables (or grounding postitve), that it empties the capacitors in PCM adaptive memory. The reason I'm asking this is because I don't have scantool available all the time, and that this error is due to a bad LPG map (I have converted this JEEP to propane).. So I would like to once again reset memory, and after PCM relearns to copy that map to a LPG controller so there would not be any differences.

Hello, Once again I have this issue for like 3 years. Trans would not shift from 2nd to 3rd on slow speed by default, it would go into neutral and after I give some more throttle it would downshift to 2nd. If I get to 40 mph or similar, once I release throttle pedal it would shift to 3rd and after that everything works fine - no problem at any speed. So my guesses are that something is stuck in valve body or governor. Until now filter has been replaced, fluid flushed (was red even before flush), TV cable adjusted, bands adjusted. The reasons why I suspect on governor valve is that this seems to be related to vehicle speed. Why I suspect about it sticking is that once (or twice) times the trans gets into 3rd after driving at greater speeds, it will work fine until i turn of vehicle and leave it for 3-4 hours, sometimes less sometimes more. I also remember that once I got stuck in some pond and engine turned off because of hydrolock, so trans spent some time in water. After that the problem was gone, and it reappeared after two months. I immediately flushed trans that time but there was no water in it however. Could it be that there is some crud that block weights in governor and make it stuck sometimes? Am I missing something or the problem is probably governor? I've also noticed that when the car is cold (like if i leave it overnight) the trans shifts from 1st to 2nd at later rpm on same throttle applied (like shifts occur on 2100rpm when cold and bit below 2000 rpm when warm)

There where no metal particles in the fluid.. However, I did some tests today. First I removed the solenoid plug. I felt only two rpm drops (when 1-2 and 2-3) shifts occured so I guess that solenoid is not stuck, because I could not feel lock up.But, same thing happened again, 3-2 downshift would not occur on speeds more than 40 mph if I don't apply full throttle. On speeds less than that part throttle downshift does occur. When going uphill this bothers me because I feel lack of power when I overtake other cars ( I feel like its in 5th speed on manual transmission, and I cant get it to 4th without full throttle). But I noticed something else that gives me the conclusion that this could be just normal behavior. I tried same thing with 2-1 downshift. On speeds more than 15-20 mph it would not occur on part throttle, but it will on full throttle. Is this normal behavior of this transmission? If it is, i guess that my problem is lack of power(engine trouble, but Im not sure because compression ratio is allmost perfect) or just the fact that this car is brick on wheels and aerodynamics play big role on 60mph+ speeds. I suspected solenoid becaues I heard about TC shudder, and I do feel shuddering (like when ABS engages) but its constant and most noticeable on speeds from 40 to 50 mph so I guess it comes somewhere else from drivetrain. I have never driven cars with such archaic transmission like 32rh, but sure it's strong as hell. Petar

Hi, Recently I tightened the bands to proper factory settings, replaced fluid et voila, no more slippage! It shifts now fine through all gears (sometimes shift to 3rd is delayed until i fully release throttle pedal, but this only happens when its cold and there is no slippage, it only stays a 1-2 sec in 2nd speed). However I still have an annoying problem like before ( this problem was here even before slippage). I notice it going uphill, it starts around 40-45mph. On light throttle (or throttle released), it will shift from 2nd to 3rd speed, and then it seems to lock up, rpms being around 1500. When I apply more throttle, rpms go to 2000-2100 and it takes a lot of time to accelerate. Only when I apply full throttle it would fully downshift into 2nd with rpms around 2500 and then I have the power I need. I dont have this problem on speeds less then indicated (then it immediately shifts from 3rd to 2nd). Knowing this my suspect would be some malfuctioning of TCC solenoid, like it keeps it locked even in 2nd speed until i press full throttle or get to lower speed. Could these be the symptoms of it? Thanks a lot for the help and advices!