Diesel engine swaps - advice required

[Ryannn]

This is a project I’ve had in my mind for a while and probably isn’t something I’ll do anytime soon/rush into, so plenty of time to look around!

I have a 1998 Jeep ZJ Grand Cherokee. It’s the 4.0 petrol, automatic with LPG. The LPG system on it is shocking and it really struggles to tow any decent weight. I’ve had it looked over by a specialist and he’s advised that it’s been made up of the cheapest possible parts, isn’t man enough for a 4 litre engine and is probably past its best with a none existent parts supply. He’s quoted me £2K for a replacement kit fitted but I’m worried about rumours regarding retailers pulling out of LPG contracts. Lymm truck stop is my most recent ‘regular’ who has taken their pump out.

So I’ve been looking at dropping a diesel engine in. Jeep did a diesel ZJ but it’s manual only and I really want to keep the auto box. I can’t find any information online about whether it can be mated to the original autobox. There’s a trend in the states of using VW TDi engines for swaps but again, with manual boxes.

Am I completely mental? Am I likely to source a donor engine? Ideally I want to keep the original gearbox so that I don’t have to hack the interior up. Should I just sink the money into the LPG kit?

My gf really likes the car and it’s the only one I own that she does 😆 so it’s in my best interest to make it a little more capable hahah!

[procrastinator]

Will depend on what box you have as to what will fit. Though I would imagine most boxes will be of a similar size. Guessing you have a straight 6 ? If so most other engine/ box packages would fit, even a Touareg v10.
I also have a gas kit on a BMW 4.4 v8, not sure if it is all there or would work on a 6. Make me an offer if any good.

[stealthstylz]

Depending on which side the front propshaft etc needs to be it'd probably be easiest to use something like a BMW X3 3.0 as a donor car for the engine and gearbox then just run modified propshafts.

[goldnrust]

I understand your thought process, and it’s a shame the LPG isn’t working out.

I’m not an expert on diesel stuff, but I have done a couple of engine swaps and my thoughts would be as follows;

If you really want the most cost effective, practical, reliable option here, then bite the bullet and sell the Jeep for something factory diesel and auto.

If selling the Jeep really isn’t an option then my next comment would be that while an engine swap can look cheap when the engine you want is available for a few hundred, it very quickly adds up. Especially if you have to get bits made. I apologise if I’m underselling your abilities, but I’m presuming that as you’re looking to get a garage to sort your LPG that you’ve not got kitted out workshop in the back garden where you can hop on the lathe
/CNC and make up versions one off bits to help the engine swap. It will probably again be cheaper and less stress to get the LPG system fixed up and running.

With that boring/depressive advice out of way, we can talk engine swaps!

Automatic boxes need to be calibrated to the engine they are matched with, so they shift at the right points and apply the right line pressure. Whether this is done by electronics or old fashioned cables and spring valves, I would count on the shift points on a 90s petrol engined car being a lot higher than a diesel engine would like. So to keep the original box, presuming it can safely handle the torque the new diesel engine would put out, you’d need to think about how to calibrate it. You’d also need to look into the bell housing spacing and how you could make up an adapter to mate it to your new engine. It would be a lot of work for a gearbox that would likely always be compromised as this was not its original intended use.

I think you’d be much better off starting with a matching engine and gearbox combo. Find a straight 6 ( as fitting an engine of broadly the same shape/layout as the original is always easier) diesel and with a bit of luck and some careful tape measure work, there stands a reasonable chance that you can make it fit without needing to cut into the transmission tunnel, as that’s something you wanted to avoid.

Another thing to consider with a diesel swap is the axle ratios. You might find the ratios in the diesel gearbox are based upon having a very low ratio axle.

There’s a couple of diesel conversion build threads on here, might be worth a browse to get a feel for what might be involved.

If you are treading the less well trodden path, it’s always going to involve some trial and error, and figuring it out for yourself rather than following a guide. That’s not to say that it’s not worth it, the best things in life are rarely easy…

[adam73bgt]

If wikipedia's information is correct, it seems as though your 4.0L and 42RE gearbox combination were used in the later WJ Grand Cherokee as well, the WJ had diesel/auto combinations with either a VM 5 pot or a Mercedes 5 pot. It's not clear which auto box they used but if the 4.0 combination fits the WJ, it might be possible to make one of the WJ diesel set ups fit the ZJ.

The VM 5 pot diesel in the WJ is a development of the engine used in the ZJ so again might be a bit easier to fit than a completely alien option.

I've no idea if that would be viable but to me it seems like a place to look as there's at least a faint whiff of commonality there

[squonk]

My late father had two of these (one was an Orvis) and they were an electronic nightmare. I would be more concerned about the communication problems in getting the Power Train Control Module and Body Electronics Control Module to work with an engine that didn't start life in the vehicle. You are going to get all kinds of problems with the security system too, and, if you get past that, you still have to get around the multitude of faults that are going to light up the the engine fault light (MoT failure) as you will no longer be using the Jeep ECU. MoT testers now use the OBD socket during the MoT Test so this will have to be made to work with the diesel (which will most likely be impossible) if you want to get an MoT on it. The transmission issue is small fry in comparison.

It will likely cost far more than the vehicle is worth to sort out the electronics - thats if its even possible to do so.

You will also have a vehicle that many insurers won't cover because its a major modification and will be difficult to sell when your done with it.

It would be far cheaper and easier to sell it and buy a WZ Jeep 2.7 diesel which is a far more modern vehicle and was available with an automatic transmission (my father had one of those too).

[Rich]

Jul 16, 2023 23:23:21 GMT squonk said:

you still have to get around the multitude of faults that are going to light up the the engine fault light (MoT failure)

Too old for that. Pass and advise.

[squonk]

Still got to get past the multitude of other problems that the electronics are going to cause though! I think the transmission is also electronically controlled on these too. I've got the manuals somewhere for one.

[giuliettaevo]

Bmw m57 engine is readily available with automatic gearbox and rwd, that would be the easiest solution. There is a 4wd version used in the X5 but you would need to look at its configuration to see if that can be used in your car. A simple thing to keep in mind is that the output shafts from the gearbox need to rotate in equal direction as on the original gearbox, that is not always the case..

M57 engine is used frequently in other vehicles and there are solutions like standalone wiringlooms available. That saves a lot of hassle.

You would need to look at your axle ratios and tyresize to see if that will work with the gearratios. There are online calculators you can use for that.

[andyborris]

If you do decide to take the easy option and sell/replace, the later Merc Diesel engine Grands are great cars, both the WH live axle and the WK independent axle versions.

The WH has the bonus of being made by Magna Steyr and is fully galvanised.

[Ryannn]

Thanks everyone, some helpful replies so far, just what I was after! Think I’ll look down the BMW route as a first stop.

Jul 16, 2023 21:30:31 GMT stealthstylz said:

Depending on which side the front propshaft etc needs to be it'd probably be easiest to use something like a BMW X3 3.0 as a donor car for the engine and gearbox then just run modified propshafts.

This was quite a common swap to do when I had a mk2 Shogun. I suspect getting the wiring right is going to be the biggest hurdle?

Jul 16, 2023 21:46:15 GMT goldnrust said:

Lots of good stuff…

You know, I didn’t even think about petrol gearbox vs diesel torque curve!

Jul 16, 2023 22:18:08 GMT adam73bgt said:

The VM 5 pot diesel in the WJ is a development of the engine used in the ZJ so again might be a bit easier to fit than a completely alien option.

Good shout, WJs are everywhere, I didn’t think there was any carryover from the ZJ, I was under the impression it was all MB based.

Jul 17, 2023 11:42:19 GMT giuliettaevo said:

M57 engine is used frequently in other vehicles and there are solutions like standalone wiringlooms available. That saves a lot of hassle.

This may be the answer, it’s a common swap for Mitsubishis.

Jul 17, 2023 13:08:52 GMT andyborris said:

If you do decide to take the easy option and sell/replace, the later Merc Diesel engine Grands are great cars, both the WH live axle and the WK independent axle versions.
The WH has the bonus of being made by Magna Steyr and is fully galvanised.

I’m open to experience but I’d previously heard that the WJ’s hadn’t aged well and threw up a lot of life ending fault codes.

[dodgerover]

Seriously you need to find another LPG installer! A full sequential install on a V8 Grand Cherokee was far less than £2k you already have the tank pipework etc in place!

MFG were the retailer who made headlines about stopping selling LPG, but have subsequently said it will only be the stations that aren't profitable or need major works.

The 4l 6 cylinder is about as simple a LPG conversion as you could get, I've seen them running well just using a 15mm copper plumbing elbow instead of a mixer!

[crockpot]

I can't add much that will help. However I did have an LPG converted XJ Cherokee about 25ish years ago. The difference between LPG and petrol was barely noticeable, it pulled a caravan with ease.
As said, sorting the gas system has to be the simplest route.

[legend]

BMW 3.0 diesels have great support for transplanting into all sorts of other vehicles. the BMW engined Land Rover facebook group seem to have resolved many of the wiring issues.

[Ryannn]

Jul 18, 2023 22:23:29 GMT dodgerover said:

Seriously you need to find another LPG installer! A full sequential install on a V8 Grand Cherokee was far less than £2k you already have the tank pipework etc in place!
MFG were the retailer who made headlines about stopping selling LPG, but have subsequently said it will only be the stations that aren't profitable or need major works.
The 4l 6 cylinder is about as simple a LPG conversion as you could get, I've seen them running well just using a 15mm copper plumbing elbow instead of a mixer!

I might try and get another quote. Mine looks like a V6 kit that’s been fitted to straight 6 engine and all the bits are from different manufacturers. He did show me the Prinz injectors he uses and they were twice the size of mine.
Supply wise, I live pretty close to an industrial supplier so I don’t think I’ll ever struggle to get gas at home, I’ve only really started to get concerned when Lymm stopped selling it.
Any recommendations for fitters?

Jul 19, 2023 7:37:35 GMT crockpot said:

I can't add much that will help. However I did have an LPG converted XJ Cherokee about 25ish years ago. The difference between LPG and petrol was barely noticeable, it pulled a caravan with ease.
As said, sorting the gas system has to be the simplest route.

Yeah that’s what I expect mine should be like. But even without a trailer on, it feels like it has a misfire if you hit a big enough hill. Sometimes I have to drop it onto petrol haha. The guy who serviced it said the injectors weren’t up to the job and the diaphragm in the mixer thing will be easily 20 years old now.

Jul 20, 2023 9:32:50 GMT legend said:

BMW 3.0 diesels have great support for transplanting into all sorts of other vehicles. the BMW engined Land Rover facebook group seem to have resolved many of the wiring issues.

Nice one, I’ll take a look.

[dodgerover]

Ask on the LPG Facebook groups or ask the firm that used to be called tinleytech for a quote on a new front end kit to fit yourself if you are competent with soldering etc.

Or ask for help or suggestions on here
www.lpgforum.co.uk/viewforum.php?f=48

[squonk]

Jul 22, 2023 10:38:50 GMT Ryannn said:

Jul 20, 2023 9:32:50 GMT legend said:

BMW 3.0 diesels have great support for transplanting into all sorts of other vehicles. the BMW engined Land Rover facebook group seem to have resolved many of the wiring issues.

Nice one, I’ll take a look.

To make this work sucessfully it will need integrating into the cars original CAN BUS system. Without doing so means that none of the instruments will work and, apparently, the Body Control Module (BCM) won't work either. This in turn means that the central locking, electric windows, radio, sunroof and just about every other electrical system will fail to work as well.

Transplanting engines into cars that require CAN BUS communcation is a very difficult thing to do unless you can find someone who has done it sucessfully before and can provide you with electronics that can interpret the BMW CAN BUS signals and convert them into something the Jeep CAN BUS will understand.

It will be far easier and cheaper to sort out the LPG system

[legend]

e39/ early X5 wiring is well understood.

www.facebook.com/groups/421628878703561/?locale=en_GB

have a shufty here

[giuliettaevo]

Jul 22, 2023 20:30:16 GMT squonk said:

Jul 22, 2023 10:38:50 GMT Ryannn said:

Nice one, I’ll take a look.

To make this work sucessfully it will need integrating into the cars original CAN BUS system. Without doing so means that none of the instruments will work and, apparently, the Body Control Module (BCM) won't work either. This in turn means that the central locking, electric windows, radio, sunroof and just about every other electrical system will fail to work as well.

Transplanting engines into cars that require CAN BUS communcation is a very difficult thing to do unless you can find someone who has done it sucessfully before and can provide you with electronics that can interpret the BMW CAN BUS signals and convert them into something the Jeep CAN BUS will understand.

It will be far easier and cheaper to sort out the LPG system

So the first question is;how much canbus is there in a 1998 Jeep?🤔

[Rich]

Jul 23, 2023 15:13:56 GMT giuliettaevo said:

Jul 22, 2023 20:30:16 GMT squonk said:

To make this work sucessfully it will need integrating into the cars original CAN BUS system. Without doing so means that none of the instruments will work and, apparently, the Body Control Module (BCM) won't work either. This in turn means that the central locking, electric windows, radio, sunroof and just about every other electrical system will fail to work as well.

Transplanting engines into cars that require CAN BUS communcation is a very difficult thing to do unless you can find someone who has done it sucessfully before and can provide you with electronics that can interpret the BMW CAN BUS signals and convert them into something the Jeep CAN BUS will understand.

It will be far easier and cheaper to sort out the LPG system

So the first question is;how much canbus is there in a 1998 Jeep?🤔

Given the 97> XJ has a basic BUS network, I’d imagine ‘some’ would be the answer.