GEMS 4.6 Engine Problems

Hello All,

I am having a few issues with my GEMS 4.6 Petrol engine since getting it back from a local Landrover specialist, who replaced the Head gaskets, due to an external water leak, and Camshaft.

I would normally have carried out this work myself, (and wish I had), but due to a family member being seriously ill at the time, was unable to.

I won't bore you with the long story, but having been back to the specialist for the sixth time without any improvement in the car, I have decided just to try and sort it out myself.

I wonder if some one would be able to help with the following:-

1) What is the maximum allowable clearance between the throttle housing and Butterfly valve. I measured mine as average 0.05 mm with one spot at 0.1 mm.

2) If I put a piece of pipe on the Drivers side Rocker cover Breather, I can blow/suck through it easily with minimal resistance. When trying the same thing on the passenger side Rocker Cover Breather, there is a huge resistance. I can only reduce the resistance by removing the oil filler cap. Likewise if I blow/suck down the oil filler hole there is a huge resistance with the breather spigot blocked off. Is this right? If not, which side is wrong?

3) Does anyone have any MAF output voltages recorded at different RPM's?

4) Finally for now, has anyone cleaned a MAF sensor and would they recommend doing so.

I look forward to receiving any advice.

Many thanks.

Why flaff about with MAF output voltages when you have an obdii port and the flow figures in rave.
I've used brake cleaner to clean a MAF which worked for about a month until it went out of range again.

Were the heads skimmed? If so were the rocker clearences checked and adjusted with pedestal shims? - If not you may have valves that are leaking because they aren't fully closing.

Where are you? There may be people close by with diagnostic equipment ready to lend a hand.

You'll need a proper diagnostics machine to read the MAF output, I've tried with my generic OBD2 reader and the output seems to be wrong.

The MAF sensor outputs between 0 and 5V and you should get around 1.4V on idle according to RAVE. Look at the V8 Fuel system section and then the tables showing the ECU connector list which shows which pin to check and the expected values.

Hello Guys.

Many thanks for the replies.

The Heads were apparently sent to a specialist in Swansea I believe, who skimmed them, pressure tested them and rebuilt them. I do not know if the rocker clearances were checked on re-assembly. I had planned doing a compression check as part of my next set of tests, so this may throw up something.

I do not currently have any diagnostic software/equipment, I have been looking at the Faultmate MSV extreme as this seems to be the only package that also covers the HVEC system as well. Un-fortunately the car has been racking up the bills recently so I have had to put this on hold.

My main problems currently are, the idle falls from its normal 625 rpm to 500 rpm when stopping with it in gear, (automatic box). Note, I have owned the car for several years and 625 rpm has been the norm, with no inherent problems. The specialist mentioned that the ECU has 650 rpm set in it as the idle not 700 as he would have expected for my year, (1997), but as mentioned, this was never a problem. There is a definite “grumble” coming from the engine, as if it is missing/running on 7 cylinders. This “grumble”, seems to be there across the whole rev range as best as I can tell. A hot start problem, but only if you try and re-start the engine say 2 to 3 hours after running it, and you have to floor the throttle to get it started.

The car tends to run very badly after the adaptive ECU values have been reset, which seems to be the starting point of the specialists I have taken it to so far. e.g. resetting them first before doing anything else. I get a very erratic idle and a general lack of acceleration/performance. I have asked on several occasions which/what adaptive values are there, which may point towards a problem, but have had no success. The ECU also does not have appeared to have logged any fault codes. After driving the car for 60 miles or so, after a reset, it runs better, which is I assume after it has adapted again.

I checked the MAF sensor output voltage on the ECU pin which was around 1.4 V at idle +/- 625. I have noticed after an adaptive reset that I have a flat spot around the 1200 to 1500 rpm. Checking the Throttle position sensor output on the ECU pin shows that the sensor is working OK. The MAF sensor values are a little un-stable and difficult to fix a reading using a multimeter. So I thought if I knew what the voltage readings should be at say 500 rpm intervals from idle to 3000, I would be able to gauge its condition better.

So far I have changed the Lambda sensors, Coolant temperature sensor, Fuel rail temperature sensor, Idle control stepper motor, Plugs, Plug Leads, Coil pack, and put a second hand MAF on which was taken from a known running vehicle. Note changing the MAF had no effect. I have checked fuel pressure which is good at 34 to 38 psi.

I am currently based in Llanelli, South West Wales, but regularly pop over to Pontypool on a weekend to see the folks.

The Nanocom Evo will do all your diagnostics for much less than the Faultmate, it's from the same company.

Thanks for the info on the Nanocom evo.

I will take a look at it.

Dear PAW. what a shame you are having these problems after spending so much with professionals!
Compression test is a good idea but as recommended by the advice given you do need to get a diagnostics done. Some things you could check yourself are:
Ignition leads on the correct way as you could have a crossover.
Air leak somewhere so being carefull spray some easystart around the obviouse gaskets etc, if the engine revs then you have found the leak. But be careful.
nano lights on the injectors to verify they are all firing.
Ask the garage which new timing chain and sprockets they put in? Stiff is the one needed. If the floppy one then its possible for the timming to be out. Also did they check the tappet pre-loads?? this is important when heads are skimmed also how much was taken off?
Lambda sensors? diagostic will reveal.
Maffs, only way is to buy a new gen one. Mozz Smith told me his car ran badly after an engine rebuild, he fitted a spare he had off a good running car result same, got a brand new on and the car now purrs!
Good luck