1988 Isuzu Trooper diesel conversion

A few more shots of the tank installation.

The solution to the filler neck dilemma was to fabricate a tube to connect the new tank to the (shortened) original rubber fuel filler hose.

I began by ordering a piece of 1-3/4" I.D. mandrel-bent mild steel exhaust, something called a J-bend. This piece of tubing is used by custom header and exhaust fabricators and features a 180-degree bend and two legs of different lengths.

Next, I took a number of measurements of both tanks to determine the location of the filler necks on each. I used one of the mounting bolt holes on the tank flange as a reference point, as these holes were the same on both tanks. Using a straightedge and a long screwdriver (through the bolt hole, to obtain a reference line) I was able to measure the location of the necks fairly accurately.

These measurements were then used to generate a CAD drawing of the two tank necks. Additionally, I drew the J-bend and the rubber filler hose. All of this information was used to determine the best way to use the J-bend to connect the existing filler hose to the new tank. The CAD drawings were then printed and used as full-scale patterns to cut the J-bend, weld the pieces together and to cut the filler hose.

The filler hose was cut just after the first right angle bend (just as it begins to travel sideways after dropping from the gas cap area). The J-bend was cut into sections and tack-welded into an S-shape for initial fitting. After determining that the fit between the frame and bed support channel was too tight, I flattened the tube a bit in the middle in order to get it to fit. I also purchased a Gates universal 45-degree bent fuel filler hose, as I needed the 45* bend to connect the tube to the new tank's neck, which is at a more upward angle than the old neck.

My clumsy welding caused a burn-through during finish welding of the tube, so I coated the entire junction with J-B Weld to seal it. The final fit is extremely tight, but it works - leak free, so far.

The other difference was in the location of the overflow pipe. I had to bend it slightly sideways to get it to clear the body bed support channel, then buy a length of 1/2" I.D. fuel hose to connect it to the filler cap (the old one was too short).

The fuel tank I removed from the Trooper had very old gas in it. As a result, semi-solid residue was being drawn into the fuel filter, clogging it. I had tried to clean the tank, but it was obvious that there was a substantial amount of residue in the tank.

My options were to either have the tank professionally cleaned (quoted at $300 and up), keep replacing fuel filters until the problem went away ($25 each) or replace the tank with a clean one ($200). I decided to go with option 3 - that's the cost of 8 clogged filters, something I thought possible based on the condition of the old tank.

The problem: the new tank was not quite the same as the old one. Aftermarket tanks were no longer available from the suppliers I contacted, so I went with an OEM unit. It seems that changes were made at some point, however, as the new tank differed slightly from the old one. The main change was to the fuel filler neck location: the new tank featured a centered neck, while the old tank's neck was located toward the rear and angled back. This difference meant that the old fuel filler hose would not connect to the new tank, leaving me with no way to fill it.

As the 4JB1-T injection pump is on the driver's (in North America, at any rate) side of the engine, the factory gasoline fuel line termination at the passenger's side frame rail near the firewall had to be addressed.

I had initially run rubber hoses from the factory hardlines up and over the firewall, down the fender and to the filter/primer pump assembly. In search of a more permanent solution, I decided to install steel lines in place of the rubber hoses, following the same route.

The new lines are formed from 6' lengths of brake and/or fuel line and are secured along part of their route by the factory clips (one of which used to keep the clutch line in place when it ran across the firewall; the other was empty), one new bracket (connected to the cruise control actuator mounting holes and running up the firewall) and a few rubber line clamps.

The new steel lines connect to the factory fuel supply and return lines at the passenger- side frame rail with short lengths of rubber hose, and to the filter/pump assembly with loops of hose. I am not terribly worried about the proximity to the exhaust where the new lines meet the factory lines; although it is close, I plan on fabricating a heat shield if necessary.

After hard farm use and two years of sitting outdoors, the brakes on the Trooper were in poor condition - the calipers were seized (along with their mounting bolts), the rotors were rusted, the pad friction material had separated from the steel backplate, and the fluid was completely black.

I repacked the front wheel bearings and locking hubs, replaced the grease seals, had the front rotors machined and installed a new set of calipers and pads.

The rear brakes received similar treatment: new rotors, calipers and pads. I also lubricated the parking brake cables and pivot points, replaced one of the parking brake cables and adjusted the system. Fresh fluid completed the rebuild.

After many failed attempts, I've finally gotten my hands on a genuine Isuzu intercooler hood scoop. A few private parties fell through (I was trying to get someone from New Zealand or Australia to ship me a scoop) and more than one supplier refused to help.

Only one outfit, All Four X Four Parts in Australia, was willing to sell me the parts. They did a fantastic job, cut the scoop free with part of the hood and all the mounting hardware intact, and even included the sealing gasket. Great guys to deal with. Check them out online.

Now I need to weld it into the hood...

As delivered, the heater hoses on the diesel engine appeared intact. Closer examination revealed that they were both torn and in need of replacement. Both hoses are shaped units, unavailable in the USA (at least, one cannot walk into a parts supplier and order hoses for this application) and, after my experience trying to find a lower radiator hose, I was in no mood to try and find something that would work from another vehicle.

The solution was to duplicate the more complicated bends in copper plumbing pipe and use standard 5/8" heater hose for the rest. All that was required beyond the copper shown above was a straight length of hose and one 90* bent rubber hose, which should be easy to find in a parts catalog.

The main issue was finding a way to duplicate the bead found on the end of factory steel hose connections, which is present to prevent the hose from popping off. I used a flaring tool to create a single flare in 1/2" copper plumbing pipe (the 5/8" die works perfectly for this, don't ask me why) and then employed a combination of 90* elbow fittings, T-fitings and 5/8" copper repair sleeve to create the tubes shown above. The flared 1/2" pipe fits into the enlarged areas of the elbows and Ts, and those oversized sections are the perfect size for the I.D. of the heater hose.

The T-fittings are present to allow for the future plumbing for the SVO heating tank and possibly a coolant heater for winter starting. They are closed off at this time with plugs (one shown above left) and a short section of hose.

After filling the radiator for the first time a few weeks ago, I immediately noticed a large coolant leak coming from somewhere near the alternator, under the A/C compressor (this was why I filled it with water initially!). I had other things to do and so let it be for a while. I was able to repair it today, or so it seems... it has not yet been pressurized, but it doesn't leak during filling like it used to.

I removed the A/C compressor and was able to spot the leak - coming from the water pipe connection at the block. These types of connections employ a metal pipe with an O-ring around the end, slipped into a machined area of the block (in this case, a bolt-on water neck) and secured with a bolt. I've seen similar designs used by Honda. In any case, this water pipe runs from the block, loops around the alternator and becomes the lower hose connection underneath. It is similar to the water pipe found on the 4-cyl. Isuzu Trooper gas engine in this regard.

I removed the two bolts, one at each end of the pipe, which secure it to the engine. I also removed the alternator heat shield which bolts to the pipe - one of the mounting tabs is visible in the photo. I could then pull the pipe out of the water neck. The alternator has to be removed to get the pipe out completely, but I was able to work with it pulled back and to the side. I cleaned the water neck surface with some emery paper and cleaned the pipe's O-ring groove with steel wool, replaced the O-ring (I used a spare O-ring that came with my Wix fuel filter for this project - the O-ring is meant to seal the sedimenter at the bottom of the filter) and re-assembled the water pipe. Common O-rings available at the local hardware store would probably have worked as well.

No leaks after an initial filling of the system; it remains to be seen whether it will hold under pressure, but I feel confident that it will.

Finding an oil filter for the 4JB1-T engine was a bit of a hassle. Apparently, older versions of this engine used a filter identical to the one used on the Isuzu C223T, the diesel available in the Trooper in the USA. My engine, however, required a different filter with rather strange specifications. The center hole is 26mm wide, making it difficult to match.

I found a page which listed a few different part numbers (go to the 'workshop' link and select 'part numbers') but none of them crossed over to any North American manufacturers. A 4x4wire member then found this page, which again lists a few different options plus an OEM number. Here is the 4x4wire thread discussing this.

I called my nearest Isuzu industrial dealer and was able to order filters based on this number. Apparently, no other Isuzu filters in the USA will fit, and there are no known aftermarket crossover parts available, so this is the only filter that will work (save for parts ordered from overseas).

As an aside, it is not a dual-stage filter like the one I removed from the engine. This means I will need to change it more often than the dual-stage interval of 7500 miles, but that's fine with me. The only other problem is that they cost $20 each!

Due to the custom pressure hose breaking at the pump fitting (due to a hose defect), I needed to re-work the power steering system a bit. The complicated pressure hose routing described earlier was eliminated in favor of a much simpler design. Instead of running to a hardline connected to the steering sector, the hose now runs directly from the pump to the sector.

The connection at the pump is a stock Trooper part. This one came with my diesel engine, but it is identical to the fitting on the 4-cyl. gas engine pressure hose (except for the pin on the side of the diesel connector - this is not necessary and I considered cutting it off). The hydraulic shop cut the hardline off the fitting and brazed on a standard threaded flare connector. This creates an adaptor fitting which can be connected to the rubber pressure hose itself.

The steering sector fitting is another stock Isuzu part, this one having been cut off the old power steering return line, which ran from the reservior to the steering sector and threaded right in. The pressure and return ports are the same thread size, so the fitting was cut off from the old hose and again brazed to a standard fitting, creating an adaptor fitting at the other end.

The hose itself is a rubber pressure hose with identical fittings on each end which allow the two Isuzu adaptors to be threaded on. This way, if the hose ever fails or deteriorates, I can just have a new center section made and re-use the fittings.

The upper right photo shows (most of) the new hose. The upper left photo shows it installed, with another short section of hose added on at the sector end to account for my measuring mistake. Next time, I will be more careful and only need to buy one section of hose!

And here is a shot of the current state of the engine bay. Messy, but starting to come together...

Not much fabrication here - the stock diesel Trooper airbox, filter etc. all bolt in without hassles. The flexible rubber intake hose fits with a little trimming. I did have to cut a small notch in the airbox cover which allowed it to rotate toward the engine a few degrees in order to fit the hose correctly.

The radiator used is a unit from a 1986 diesel Trooper. The hose inlet/outlet are on opposite sides of the radiator (as compared to the radiator from the gas Trooper); the core is also thicker and the tanks are larger, it's much more robust overall. The radiator and shroud are bolt-in items, no modifications needed to mount to the chassis.

The upper radiator hose, shown above right, is also from a diesel Trooper. It required minor trimming to fit.

The lower hose (above left, shown from underneath, with the near end being the engine end) was problematic. The engine-side inlet is larger than the outlet on the radiator and is located slightly to the side of the outlet. I tried to find a hose that had the curvature I needed which also changed diameter at some point, but I was unsuccessful (not to mention annoying to the fellows at the parts counter). Additionally, the distance is too short to use any sort of universal flexible hose.
I decided to have the radiator modified and have the outlet enlarged to match the inlet tube on the engine. With this done, I found that Gates hose #22364 has a curved section that fits perfectly (after removing a 90-degree bend at one end). According to the Gates site, this hose fits a 1998-2001 Ford Ranger or Mazda B2500 pickup. I am not sure which hose it is, or which engine it fits, but these trucks are common so I don't anticipate any problems finding spares in the future.

These photos show the pump connections and pressure line routing for the power steering system. The new bracket and hardline are visible in the photo on the right.

The power steering system was completed using a custom flexible pressure hose, a fabricated bracket to hold it in place and a new hardline to connect the pressure hose to the steering sector.

The pressure hose uses the pump end that came with the engine (although this is the same fitting the gas Trooper hose uses, just not as long and full of curves) and the opposite end is the same as the gas Trooper hose as well. I believe this hose is actually a Rodeo hose which has been modified at the pump end, as the Rodeo hose pump fitting looks to be correct at first glance but is actually different in inner diameter and will not work with the Trooper pump. Thanks to Jerry Lemond for the hydraulic fabrication work and consultation on this stage of the project. As far as I can tell, the diesel and gas power steering pumps are identical save for the pulley.

The pressure hose then travels down along the side of the radiator and is secured by a bracket I fabricated. The connection is the same as the stock gas Trooper and uses the top half of the factory bracket to retain the hose. The lower half of the bracket is a piece of angle iron. The bracket attaches to the frame on top of the bracket that holds the power steering hardlines that run along the frame, below the radiator.

The new hardline was made from a length of 3/16" brake line (I believe that's the dimension - I matched the old hardline I removed from the truck) which was bent to connect the pressure hose to the sector. The fittings on the ends were taken from the old hardline and re-used. It was time-consuming to get the bends just right, as the line is fairly short and has to be pretty much perfect or the threads won't start correctly in the sector or at the pressure hose.

The 1986 diesel Trooper uses the fluid return line as the cooler and this line is looped from the reservior to the sector, running along the frame below the radiator. The gas Trooper cools the fluid using the pressure line, as the pump is on the passenger side of the engine bay and the pressure line has to run across to the opposite side anyway. I removed the old pressure line and so was left without a cooler line. I decided to install the diesel cooler line, as it was the easiest solution (it bolts right in, no modifications needed).

The reservior was connected to the pump using a length of silicone heater hose, which is oil-resistant. The return line (below the radiator, as factory for diesel Troopers) is connected to a length of transmission oil cooler line which runs from the hardline up to the reservior.

If I had to do this again, I would modify the pressure hose end to match the return line from the gas Trooper, as the gas design reservior-to-sector hose screws into the sector. This way, I would be able to eliminate the bracket and hardline I fabricated and attach the new pressure hose directly to the steering sector. This would have saved hours of work.

Here is a photo from underneath which shows the new clutch hardline routing, new bracket and stock flex hose used to connect the slave cylinder.

The diesel clutch slave cylinder is on the opposite side of the bellhousing from the gas version (the diesel is on the driver's side), so the factory hydraulic line running up and over the engine to the passenger side of the truck would not work.

The flex hose bracket was retained and modified to be used in the new installation. The bracket originally bolted to a small hat-shaped bump on the underside of the body and incorporated a small lip which caught the edge of the bump to keep the bracket from spinning on its mount. This lip was cut off to give the bracket a flat mounting side, creating a simple L-shaped piece. Two holes were drilled into it and two bolts were welded on to be used as mounting studs. Matching holes were drilled in the body on the driver's side and the bracket was simply bolted on. I had to remove the exhaust shield to do this as it was in the way - a cutting torch makes short work of this. In fact, it would be best to do this early on in the project, as the shield is no longer needed (exhaust exits on the other side of the truck now) and the shield gets in the way during transmission installation. I used spot welds as reference points to line the bracket up, as they're visible from underneath and inside the truck, and marked and drilled from the inside the driver's footwell.

The clutch hardline was removed at the damper box (small part on the driver's fender with clutch lines going in and out; also has a bleeder on top) and cut just after its 90* bend at the firewall. I did this so I could retain the stock line, as it changes diameter at the damper box and I was unable to find a matching new line. At the firewall, a new piece of hardline is joined to the old using a brass union. Metric line is not needed, SAE line is the same diameter (I believe it was 3/16") and the union and flare fittings are all SAE which were easily obtained. After the new union, the new hardline travels down the firewall and loops up and under the flex hose bracket to duplicate the stock routing. I simply used the old metric fitting on the new line to join it to the flex hose. The stock 1988 Trooper flex hose fits the diesel slave cylinder perfectly, so a new replacement part was used.

A rebuild kit for the clutch master cylinder and a thorough bleeding of the system completed the job. It works quite well - I was concerned that the master and slave cylinders might be mismatched, but the clutch operates perfectly. No grinding into gears with the engine running and engagement is good.

The diesel slave, in addition to being mounted on the driver's side of the bellhousing, also is a different casting than the gas unit. It is possible that the innards are the same and that the gas rebuild kit would work if needed. Another thought is that since the V6 Trooper of the same body style (GM 2.8l V6) shares the diesel's slave cylinder location on the driver's side of the bellhousing (if memory serves, anyway), the V6 hardware might be a direct fit for the diesel. Also, the V6 slave and the diesel slave cylinders may be the same. I guess I'll find out when mine fails. Finally, I recommend the Harbor Freight $12 double flare toolkit highly - very cheap and created leak-free flares. Just be sure to slide the fitting onto the line before flaring!

Below are a few shots of the completed throttle cable. The stock (gas engine) cable was much too long for the diesel, as the intake sides of the engine are different. Also, the engine-side bracket was wrong on the gas cable. The diesel engine came with about 5" of cable, cut short during removal by the wreckers no doubt. Even if it were complete, I am sure it was from a right-hand-drive vehicle and would have been much too long for the new chassis anyway.

I bought the stainless braided universal throttle cable at a local speed shop. It had an engine-side end made for a carburetor, but was otherwise well suited to the application.
The upper left photo shows all the parts together. It was about twice as long as I needed, so it was cut back to fit.

The upper right is a shot of the pedal assembly. I cut the cable receiver off and welded it back on 90* rotated from its original position to accommodate the shackle that the new throttle cable employs (originally, the cable met the pedal with an in-line rubber cylinder, which was more difficult to duplicate than it was to modify the pedal to accept the new cable end). It fits perfectly, as luck would have it.

The second row photos are of the engine-side cable retainer nuts (left) and pedal-side shackle and firewall mount (right). I added the washers to secure it in the firewall, as the hole is larger than the cable mounting nuts. The engine-side retainer fits just like the stock cable retainer, no modifications needed.

The lower left photo shows the cable wire stops I bought, along with the stock end of the gas throttle cable (diesel is identical). My good friend Tom, who has been helping me with advice and labor throughout the project (couldn't have done it without the assistance!), found these wire stops advertised on a go-kart parts site.
I wanted to duplicate the Isuzu engine-side end, also shown in the photo. It is similar to a bicycle brake cable, only taller. The go-kart wire stops employ set screws to hold them to the throttle cable's inner wire, and seemed perfect for the task. I found some locally at a small engine repair shop - 2 for 50 cents! At any rate, the wire stop on the left is shown with the Isuzu bushing from the diesel cable installed over it. The center wire stop is as purchased, and the rightmost cable end is the Isuzu part.

The lower right photo is a shot of the completed installation. I just need to free up the pedal stop bolt, on the driver's footwell, so I can adjust it properly to the shorter travel the diesel engine requires. A few days soak in penetrating oil should do it.