Mogwyth

Mogwyth

New Member
Started out with 4.0 V8 with SAI which died.

Reconditioned (non-SAI) 4.6 V8 fitted in October, 1200 miles were done on petrol only with no apparent problems average mpg was in excess of 18.

At 1200 miles a full service was carried out and the LPG recommissioned, shortly after this the problems started (or did they?) fuel consumption went off and a hesitancy developed between 1250-2000 revs making the motor almost undrivable on gas in 30-50mph traffic, it's barely noticeable on petrol but there, fuel consumption went as low as 10mph.

All four lambdas have been replaced. ECU has been replaced.

The vehicle seems to have plenty of power.

Diagnostics on both Testbook and std diagnostics show no faults but I am being told it's not going closed loop.

Now going back to "or did they" well looking back on the "run in", the 1200 miles were done on a holiday to Kent, thinking about it now on the outbound leg up 20-22mpg was achieved on the return this was more like 18-20mpg, us driving it harder or the fault developing? Not sure but the hesitancy is so slight on petrol it is possible we may not have noticed it.

Now thoughts, I looked at the MAF sensor today, inside is a wire and a flat mirror like surface, this surface looked a bit grotty, what does this do? Could it be a factor? I have swapped it for another cleaner looking one, not been out yet.

It appears that the MAF for the 4.0 and 4.6 are different part numbers, what could be the difference and would it cause the problem (they are £150 or thereabouts). Secondly the Coolant Temp. Sensor is different for a SAI model and non SAI, could this be a factor? For £20 I plan to replace it anyway.

Yesterday I went to Leicester, mpg for 110 miles 60 petrol, 50 on LPG gave an average of 22, running on just gas for 150 miles gave 16ish, hesitancy is still there though.

Oh and one other thing the guy at the garage said on Friday that fuel was not going above .35 whatever that means.
 
Since fitting the new ECU fuel consumption has gone from 22.43 to 16.24 to 14.48 over 387 miles. Changing the MAF made no difference to the problem, if you feather the throttle or floor it you can get past the problem, try to drive normally and it's as if there is not enough fuel being delivered!

The garage are saying the only thing they can think of is disconnecting the engine loom and checking each and every wire for damage.
 
What's the oil consumption like?
Should have gave me a call I was about yesterday
Are you running the cats still?
Have you tried running it back on the 4.0 tune?
 
Hi Stu,

Not really monitored the oil consumption, I put maybe a pint in yesterday after doing the 390 miles but didn't check it before and it's been with the garage so long I can't remember the last time I checked it.

Not touched the cats.

It's still on the 4.0 trim, Dynachip who coded the new ECU said they couldn't set it to the 4.6 trim, something about the BCU and needing the key with the transponder in which we don't have, mind you they did better than our local LR specialist they weren't even certain they could code the new ECU despite having Testbook.

Bill
 
Ok Bill I would start with resetting the adptives do a oil consumption check too
Currently have problem with a customers engine his is also a piston ring problem due to lacquered bores causing hi oil consumption brought on due to failed lambdas and coil pack failure just a few ideas to try
 
Lambdas have less than 500 miles on them genuine LR parts, new ECU was only fitted on Friday so we were on a clean sheet there. Coil pack was checked 1350 miles ago in an effort to correct this problem and found to be not original but OK.

Cheers

Bill
 
As a general point, crank sensors can start to have problems. If the signal gets weaker and if the sensor or even the timing gear that provides the impulses get dirty, or the sensor starts to pick up EM interference, by the shielding breaking down, then this can mean that the ECU is seeing variable engine speed and timing and fueling can be affected.

This gives hesitation and drivability issues/problems on many different cars. I don't know the V8 set up, but these can cause problems after 60,000 miles or so.
 
MAF sensors can give problems from 40,000 miles up. I've had 3 replaced on different cars at 45,000, 71,000 and 75,000 (already gone). Age - anything over about 6 years.
 
Throttle position sensor is another that can give a jerky acceleration. The TPS is important for mixture enrichment during acceleration. When they wear, it is usually around part-throttle position where it gets most use. The track gets broken up and the ECU doesn't know what's happening. You can get the engine running , then disconnect a TPS to see if it changes the behaviour. The other working sensors provide some redundancy in the system, so the engine will still run, but acceleration will be affected.

If disconnecting it makes it worse than it already is, then you need to look at another sensor.

If you can read what the ECU is seeing, look to see what the TPS signal is doing. Or check the resistance of the TPS across the terminals as you open the throttle slowly - see if the resistance jumps to open circuit or zero resistance.
 
One point is if you have a seasoned/ run in engine popping sensor connectors on and off will not be an issue but on a relatively new engine it will spell disaster bore wash and more faults not advisable

Ok rather than looking at the electrical how about the mechanical whose followers and cam are you using?
Were the rocker arms replaced?
 
I would still ask the question on the followers and the cam and who the rocker Arms are from also if the preloads on the rocker ATM pedestalls were done too
 
I only suggested the TPS because it is there to enrich the mixture during fast/snap throttle openings, and to give a zero throttle position. The airflow meters and lambda sensors will make sure that everything runs correctly, but might go lean during snap throttle openings without the TPS, or if the TPS has failed.

You could try a compression test. A sticking valve or followers getting pumped up and not releasing their pressure could lift a valve and you would be working on less than 8 cylinders, and fuel economy would definitely go down.

Did you run the cam in as directed, did you use cam lube on start-up or did the engine builder use it? If cams don't get treated correctly on the initial start, you can turn them to scrap pretty quickly, especially if they are high lift. On running new engines, at least 10-20 years ago you had to use high Zinc Dithiophosphate content cam lube, and many new oils don't have enough for engine longevity.

Are you using a SM spec oil? Some oils just aren't good enough for older designs of engines with higher cam loads, older oil specs of SL or SJ are better. The HTHS value of the oil is also important.

I hope they put new followers in with a new cam, because old followers can wreck a new cam. They must always be changed together.
 
I'll see if I can find out Stu.

RM, the garage did all the build work as per the engine suppliers instructions, the vehicle was then run in at max 2,000 revs for 1100 miles on petrol only again as per the suppliers instructions, during this period it returned average mpg of around 20 and a maximum of 22 (just checked my records). The problem developed in the space of 100 miles and fuel consumption always returns to at least high teens when the ECU is reset but then gradually deteriorates. Oil is the correct spec the garage are very hot on that sort of thing.

It was a full engine plus new water pump, all that was reused from my was the ancillaries, manifolds and sensors.
 
Ok this happened once the running in was done and you switched to gas?
Then I would consider the gas running to lean and when on petrol it is running rich to compensate then causing the rough running at a guess
If that is the case try running constantly on petrol to see if it improves would be the first port of call
 
What LPG system are you using? I have heard of some systems causing problems, where the LPG system hasn't been calibrated properly or the lambda sensor wires have been cut through, and the difference in the fuel injection duration on gas is so different that the ECU recalibrates itself, such that they don't run properly on petrol again.

This might need a rolling road session, checking the air-fuel ratio running on both fuels and getting the ECU controlling the LPG injectors to do the correct conversion when running on gas, such that the normal ECU is unaffected.

Have you got a fuel pressure regulator that is sticking - not actually keeping the fuel pressure in spec, either for petrol or LPG? LPG regulators need filters to stop them getting gunged up with oily deposits from the LPG.

A temperature sensor going awol might have an effect, but checking their resistance and value that the ECU sees is necessary. The ECUs are calibrated for specific temperature sensors, where the temperature sensor resistance curve (resistance vs temperature) determines the temperature that the ECU "sees".

The only sensor that gives the data for the ECU to recalibrate the actual fuelling is the Lambda sensor, the crank and airflow sensors give the table positions, where the data is inserted/recalibrated.
 
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Can you check on the 0.35 concerning the fueling. If this is a lambda value, then your fuelling is way too rich, and did you say it's not going closed loop?

If the temperature sensor isn't working - might be infinite resistance, then the ECU will throw in as much fuel as it can, and closed loop operation only occurs when the ECU detects that nearly operating temperature has been reached, otherwise it will stay in open-loop mode, throwing fuel into the engine, just behaving as though it is permanently on cold start.

It might not be the coolant temperature sensor, but the connector or the wire between it and the ECU, or the earth, depending on the sensor design - might be a bad engine earth.

Or it might be an airlock that means that there is no coolant on the temp sensor, thus not getting the proper temperature.
 
LPG system is Romano based and worked fairly well with the old engine despite having an undersized vaporiser, the system has been properly overhauled since the new engine and things the the vaporiser, pipes and solenoid uprated to cope with minimum 300bhp, it's even properly registered.

I'll digest the rest when I get home

Cheers

Bill
 
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