Hi.

Our Mitsubishi L200 recently suffered a partial head gasket failure. We noticed a small amount of coolant ejecting from the coolant overflow bottle every couple of days. We carried out test and proved that the combustion gasses were weeping into the coolant system, but only when under load. So, the truck was taken off the road for a cylinder head overhaul before any overheating issues. During disassembly, it was found that the cam timing was one gear tooth out, and had probably been like that for some time before we purchased the truck, The head was skimmed and crack tested, no issues found. Valves were reseated, followers adjusted and all put back together. The truck started effortlessly after the fuel system was purged and sounded a lot quieter than before (maybe as the timing was correct now).

After taking the truck for a 10 mile gentle road test, we were only getting 17mpg, it is an auto so expect it to be a little lower than my manual returning 30mpg daily, but before the head rebuild it would always return 26 to 30mpg without fail. There is no black soot from the exhaust, eliminating overfilling, the EGR has been blanked off and has been for some time, and no noticeable increase in oil level, hopefully eliminating a leaky injector bleed off pipe. I am adamant that the injectors were returned to their original cylinder so as to not confuse the ECU coding.

Any advice on where to look would be appreciated.

What year is it ?

Sorry, forgot to state, it’s a 2008 L200 2.5 DI-D Diamond Auto.

I would be looking at a fuel leak somewhere. Either the return pipe from the head to the pump or the return rail inside the rocker cover between injectors

I’ve checked for leaks everywhere. But nothing found, no smell of diesel, no oil slicks on the road. As for the return pipes, the truck has now covered 500 miles since the head gasket replacement, and the oil level has not moved, still on the maximum mark. I’m well aware that these can leak so have been checking the oil level every couple of days and no issues found.

To prove the MPG we filled the tank to the brim and ran the truck for a week, then filled it again and noted the amount of fuel needed to brim the tank to get an accurate calculation for the MPG, My wife has just filled the truck once again from just under 1/2 a tank and managed to fit 7.8 gallons in. This the second time in two weeks that we have done this......

1 - 150 miles, 7.88 gallons =19.03 MPG
2 - 128 miles, 7.42 gallons = 17.2 MPG

NOT GOOD!!!

The truck would usually return around 200 miles for 7.42 gallons of diesel! About 27 MPG and has done so ever since buying the truck 2 years ago.. The truck has consumed an extra 3 gallons in 128 miles, definitely no leaks anywhere, no black soot when driving OR accelerating, no loss of power, no loss of coolant and no fault codes found.......

This is a difficult one.

Filters, fuel pump, mixture and injectors would be my first ports of call. I know you stated that they were inserted as before the rebuild and no leaks, are the wires seated properly and in the same order? Is the fuel air ratio still the same? (and how close to Edinburgh are you?)

Everything went back as it was prior to the head removal. I couldn’t be further from Edinburgh, I’m on the south coast 6 miles from Portsmouth.


Update.

The L200 was taken to a Mitsubishi specialist and no faults were found with the vehicle. They suggested that I recheck the valve clearances and maybe return the cam timing back to the incorrect timing as found prior to the head removal. So the inlet manifold was removed, and before removing the rocker cover, I checked the engine compression at cranking speed. The results were as shown.....

Cylinder 1 - 24 Bar
Cylinder 2 - 25 Bar
Cylinder 3 - 25 Bar
Cylinder 4 - 26 Bar

The specifications for the engine state 31 Bar at 250 RPM, so as cranking speed is lower and it has covered 190,000 miles, I don’t see any issues with these values. I then went on to check the valve clearances (0.90mm inlet & 0.14mm exhaust), all were perfect. I then altered the cam gearing to return the cam timing back to the incorrect position, as found when removing the head. So to recap, everything has been returned back to the as found state prior to the head removal, and guess what, still only 17 MPG!!!

The MPG has been calculated by filling the tank, driving 120 miles, re-filling the tank, noting the amount of fuel needed to fill, then calculating the MPG.

Next I will be removing the injectors and have them tested (3 of the 4 were reconditioned and recoded prior buying the truck), if all are ok, I fear it will be off to Mitsubishi!!!

I have absolutely no idea what could be causing very poor fuel economy when the truck starts and drives perfectly?

I plan on removing the injectors next week and have them professional bench tested.

Wow , so if my calculations are correct you put about £32 worth of diesel in after 120 miles

Quote: ronniecabers wrote in post #10

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Wow , so if my calculations are correct you put about £32 worth of diesel in after 120 miles

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Fuel pump pilot learn. Injection quality relearn.

Honestly the truck runs beautifully, no smoke, cold start and hot start perfect, last calculation, £50 to 130 miles!!!

As for someone syphoning diesel off overnight, very doubtful as very rural location, private drive, no issues before head removal, the trip computer is showing 16 MPG average, fuel gauge drops as driving and appears to be in the same position the following morning. None of our other vehicles have any fuel loss issues.

The Mitsubishi specialist did a re-learn on the pump but the ECU would not allow a re-learn (or I think they quoted an SQP or something) on the injectors.

Our local motor factors listed a Ford specific oil, 5/30 I believe, that was what was put in last oil change some 6000 miles ago, and what was used once again,

All filters are good, last changed 6000 miles ago along with the oil.

I will have the injectors tested, but have a bad feeling it’s going to be an ECU issue. I am a bit OCD when it comes to diesel fuel systems and cleanliness, they are so delicate and expensive if your not methodical.

My 5.0 V10 tdi Touareg is more economical than the L200!!!! Not as useful though!

I will update with my findings.......