Thread: 3.5lt EFI day to day fuel economy

Must have been different on the Disco?!

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So I may have found my economy issue...

After the old girl "broke down" a couple of weeks ago, I scored the D4 for a couple of weeks so i could get into working out the problem properly instead of just getting it going.

Well after a few little tests, I ended up changing the fuel filter and all ran as it did previous.

THEN I had my appendix out and everything came to a halt until yesterday and today.

So after ready on here about setting the dizzy air gap and other slight adjustments, I braved the pain to get started and found a whole bunch of little issues.

The dizzy cap and rotor button had pitting on the terminals. The vacuum advance didn't work. The vac supply to the reservoir was off of its fitting and split, as well as the vac hoses to the pressure regulator were well vanished. A couple of the sensor connectors were dirty.

The other random thing was that some of the intake manifold bolts were loose.

Also the ball joint and tie rod ends have bit of slack, which I think has caused the LHF tyre to scrub and explains the random direction change.

So as well as fixing all of that and resetting the timing I replaced swivel pin seals, replaced the diff oil and while I could get to it, changed the thermostat for a "warmer climate" 75 degree unit. I thought I'd try this as it averages 30 here all year and in the short term I have no plans to take it below the tropic of Capricorn. Kinda hoping the cooler operating temp will help reduce fuel use a little.

Now I have only taken it on short drive and it felt good. Time will tell what it has done to the economy. I am also yet to service the engine and trans.

I wonder what else I can find that's not up to the task...

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One of my brothers has a 1995 D1,3.5 injected.It gets around 14l/100 around town and 12l/100 on a run,at best.Basically stock,apart from a bar.Manual.

He bought it when it was one year old,now has over 350000k on it and has hardly had an issue,actually has less gone wrong than any LR i have ever owned.

Weeping coolant from the heads was the only real issue,easy fix and new cams at the same time as they were worn,at 300000k.

Where was the coolant leaking from? That was actually how I found the loose manifold bolts, just took a stab to see if I could tighten them and I actually got a fair bit from them.

Yeah, while not actually knowing what the real kays are, I believe that prior to me the girl used to pull vans a lot, plus the work I make it do AND the fact that I got her at a indicated 217k and it only shows 275k after 6 years of lots of travel and off road work, it might actually be time for a rebuild.

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Originally Posted by Konradical

Where was the coolant leaking from? That was actually how I found the loose manifold bolts, just took a stab to see if I could tighten them and I actually got a fair bit from them.

Yeah, while not actually knowing what the real kays are, I believe that prior to me the girl used to pull vans a lot, plus the work I make it do AND the fact that I got her at a indicated 217k and it only shows 275k after 6 years of lots of travel and off road work, it might actually be time for a rebuild.

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The head gaskets were leaking coolant,you could see it dribbling down the block,only minor but needed sorting.Common problem with these engines,as is worn cams.The new cams did give it a smidgen more perk,but i think they were slightly different than the originals.
I complete rebuild is a big job,i wouldn't do it unless definitely needed.

The hardest part of a rebuild for me would be getting the machining done and sourcing a new set of heads if needed.

Oh and finding the time..

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Hi Konradical,
I wouldn't worry about a rebuild just yet. To get to the bottom of your problem, first do the compression check as you said, check fuel pressure in the cruise, and then check the vacuum is steady via vacuum gauge. Then being a mechanic you should have access to a smoke machine to check for intake leaks. Once the health of the engine and intake is confirmed you can move on to the next step.

Why intake leaks ? any leak will affect the output of the airflow measurement to your PCM. It will feedback a non-typical value to the PCM/ECU. I assume yours is the hot wire/14CU PCM. Being an 89 model it should be a 14CU PCM. These early and simple systems move to a rich map if they see non typical airflow outputs per load point. I know this because of my USB oscilloscope. I connected it once to a rich running RRC and we could easily see the injector open time up around 3.5ms at idle and by simply cleaning the MAF or swapping for a known good, we saw the PCM slowly adapt to the now ?acceptable parameters? and she slowly adapts the fuelling bring it down to around 2.9ms ? about a 20% reduction. This is ?hard evidence? gathering.

As a mechanic you must have someone in Darwin with an oscilloscope in their workshop ? say a PICO. If so, rip up there after you do the tests above and get them to check it out.

In this day and age most workshops must have a fast oscilloscope to observe the outputs and inputs. Otherwise you are just stabbing in the dark and end up parts swapping bit by bit. The internet BTW is filled with baseless suggestions to change this then that etc. ? all that happens is good sensors are tossed into the bin. Rule one is always gather hard evidence. Yes, you can do all the resistance tests listed in the RAVE manual, but this does not test the item under load. An injector may pass a resistance test but fail to close on its pintle and leak continually. A TPS/ coolant temp can show correct top and bottom resistance values but if the 5V feed is low due to corrosion the feedback voltage curve/waveform will be crap. Certainly check it all according to RAVE, but you can be led astray and make false conclusion as to the culprit.

If you don't have access to an oscilloscope the next best thing to find out if the PCM is over-fuelling is to buy a wideband kit from WBo2.com WIDEBAND AFR/LAMBDA (Tech Edge) in Australia. Be careful on how you weld in the bung ? orientation is everything. This will tell you exactly where your PCM is fuelling. Dougal on this forum can be contacted with typical values. My 1992 RRC sits at 13 at warm idle and about 14 + in the cruise. It is high compression 10.5, so I have to be careful of detonation ? so run a little richer. With two wide band sensors you can see how each bank is fuelling. This is important because it only takes one bad injector to richen up one bank. With a single oxy sensor you only get a mix of bank 1 and 2 and so with a rich reading you have no idea which bank is the culprit.
It is interesting that there was no change when you took of the roofrack because as you know drag on the car is a huge factor ? tyre size, underbody turbulence and roof rack. The enormous vortices created by the large tyres and now exposed diffs/ axles etc. will be a large proportion of the cars total drag.

To illustrate roof rack drag only - 4X4 Australia did some testing with a petrol patrol some years back. With typical camping gear in the back economy way 14.4/100. Putting it all on the roof rack (swags and jerrys etc.) returned 17.1/100 ? 20% increase. They then took off the roof rack and put it all into a 900kg jayco pop-top camper ? 18.4/100 ? only 27% increase. So drag has far more effect on power required/fuelling than weight. As the power required goes up due to drag, the maps on those early PCM/ECU would probably move to a richer fuelling to be safe. With no oxy sensor feedback they would probably trim several percentage points to the overly rich side. You should see this with the wideband sensors.
I have given you my ?roadmap? on tracking down fuelling issues. With or without OBD, finding someone with an oscilloscope is a game changer and will sort your issue for the minimum cost and time. Hopefully you will get to the bottom of the over fuelling.

Good Luck. BTW ? if you get the wind band setup, you take it with you as you move onto other cars, and if you buy the right one you can tune your diesel cars with it as well.

Sorry about the crazy punctuation in my last post. I composed the message in Word and then cut and pasted. All my dashes and apostrophies were converted to question marks ? HTML coding??
As a postscript, wide band sensors are really good diagnostics tools after checking all the basics first.
If you have a vehicle with poor economy, you will quickly know if there is over fuelling or just high but correct increased fuelling to keep up with the new cruise power requirements due to extra drag or weight.