Intermittent Miss

[poleonpom]

Having been abusing the RR during my move to Ballarat, on the last trip back the old girl had a couple of episodes of power loss. The car lost power and then came good again.

About 12 months ago I changed the Cps, the crank sensor and the MAF. I've always suspected the MAF as the car hesitates before taking off and in hot weather occasionally stalls.

When cold the car is fine, but when hot it misses once in a while. It's had a new fuel pump and filters and was treated to a service before the move.

I'm thinking ignition coils? As they're getting on a bit.

As always, your collective wisdom is sought

[PeterH]

I would replace the plugs, mine had weird power loss issues going up the westgate bridge. Turned out it was a plug on the way out, changed them and all good since. Could be leads too, although from memory you put some good leads on yours I think.

[Hoges]

On the basis that it's generally OK when cold but misses when it's hot, is symptomatic of a Hall-effect sensor losing its magnetic properties when hot. Seeing you have replaced the cam and crank sensors relatively recently I'd next have a look at the MAF as suggested.. perhaps it just needs a clean.

One of the symptoms I discovered of a poor performing MAF is when in cruise control on a long ascending grade at around 90-95 kmh in 4th gear, the auto trans, instead of releasing the lock up on the torque converter and dropping back to 3rd gear, would suddenly drop back to 2nd gear and rev to 4000+ rpm:o which was somewhat disconcerting. If I drove the same route without cruise control, the trans. would just break from the lockup clutch and the torque converter would do the rest. When I later changed the MAF, the transmission was much better behaved in cruise control and "held on" for a lot longer...

Specified spark plugs are supposed to last reliably past 70,000km. If older I would replace. I replaced my ignition coils at 130k km ...there was no burning evident but I had the heads off so....

another source of occasional miss when air intake is quite hot, is a lean mixture...make sure that all hoses are secure.

Recently had problem with the plastic hose tail which screws into the inlet manifold and receives the hose from the PCV outlet on the RH rocker cover. The hose tail was split across the threaded end- I'm guessing from thermal fatigue and when the under bonnet temp was around 55 deg+ I'd get rough running especially in stop-go traffic because air was being sucked into the manifold after the throttle valve body and leaning out the mix beyond the range acceptable for the automatic long and short term fuel trim adjustments. hope this makes sense :eek:

I replaced the plastic part with a brass one (1/4 BSP from Repco... $3) making sure the thread was well wrapped in PTFE thread tape to minimise chance of brass thread galling in the aluminium housing. No more rough running, hesitation ...problem solved.

If you have the Torque pro app or similar or better still a Faultmate, they can read the faults stored in the engine EMS. Records of Rough running events/misfires etc are all there.

[TheTree]

HI

What Hoges said :angel:

I just wanted to add that the best app i found for iPhone is DashCommand, it's not free but like torque it reads the ecm and returns all the fault codes.

It has helped me narrow down my misfiring on gas to low fuel pressure so I am going to replace my fuel pump soon.

Steve

[poleonpom]

Guys,

That's great advice, for some reason I never thought to connect my Torque Pro, I'm also going to look at Dash command. Above all, maybe it's time to take the plunge and buy a Fault mate.
The MAF is still my primary target as I've never been happy with it, I bought a cheap replace at the time. I have also not changed the HTC leads, so with 18th xx on the clock I think this is a bit overdue...
As part of the service I replaced all the plugs, but plan to give the beast the once over sometime this week.

[PeterH]

Can't recommend a fault mate highly enough, it will point you in the right direction when trying to dignose any faults, may even make you aware of things you didn't know were a problem. Excellent investment for a P38.

[wayneg]

Have a look at the Lamda sensors as well, these seem to get overlooked but can be the cause of wrong fuel mixtures

[poleonpom]

Does a 96 Gems have Lamda sensors?

[wayneg]

Best read this......http://www.aulro.com/afvb/p38a-range-rover/50236-p38-owners-oxygen-sensors.html

Then get under the car for a look see.

[poleonpom]

Ran Torque Pro and no faults came up - bit of a relief

Had a look under the bonnet and started off with Hoges advice. The pipes from the rocker covers to the Plenum have gone soft and one of them had a split. I cleaned them out and sealed the pipe and now the engine runs well without the hesitation at take off - Result!

I did notice that the surfaces behind the butterfly look a bit dirty, does anyone have any advice as to what to use to flush out the plenum chamber?

Feeling good about the P38 again, and now I need to put in an order for long-overdue parts

[PeterH]

Glad you are seeing results, always a relief!
I use a spray can of Throttle body and carby cleaner and a clean rag, I think it's by CRC from memory.