Misfiring RRC 3.9

[MikeAK]

Hi,

Just been looking at a 3.9 thats developed a misfire. Was driving fine then over about 10 miles went to being almost undrivable.

Idles fine and will rev up a bit but when it gets to about 3200rpm it like its hit a rev limiter, won't go any higher regardless of throttle opening also much popping in the air cleaner. Lambda sensors show it going lean above about 2800 even on max throttle where it should be going rich.

Seems like fuel starvation so I checked the fuel pressure and its fine 35psi at wide open throttle. I have a spare ECU and AFM so swapped those, made no difference.

Haven't checked what the sparks are doing yet because it seemed so much like fuel starvation I jumped in on the fuel side of things. Checking sparks is tomorrows job, but if anyone has any ideas before then please shout up.

Thanks

Mike

[rocksteady]

Hi there, sounds like the cam to me. Take the rocker covers off, and check that all the valves are opening.

[Quagmire]

A cam would not run fine and then go wrong over a period though- it'd just be pants all the time.

Mike, check the sparks and then report back- there are EFi diagnostic manuals on here somewhere- check tech archive.

Popping into the intake is a symptom of lean running (i think).

So does it run fine from cold then go bad when its up to temp?

[SteveRK]

Throttle position sensor?

i fiited a new *hitpart unit recently that caused the engine to stall over 1500 RPM - the resistance was all to pot.

I'm still waiting on a refund.

[Hybrid_From_Hell]

With engine hot and running squirt some WD40 on each exchaust manifold and report back

Those cyls firing will burn off is secs, those not will stay wd40'd

Report back on which are aren't

Also check the tech archive for the diagnostic manuals I put in there

and another vote for not the cam, more likley spark or fuel, need

to narrow it down

Report back

Nige

[MikeAK]

Hi again,

Been through the Hotwire diagnostic as in the tech archive, all sensors etc read sensible values read at ECU connector.

So had a look at ignition. Checked timing 4 degrees at idle and advancing correctly. Put strobe on coil lead and it seems like at idle there is the odd missing flash. When revved up the strobe suddenly goes dimmer about 2800rpm but not sure if this is a red herring maybe the strobe can't keep up with the rate of sparks on the coil lead.

So then tried Nige's tip of spraying WD40 on the exhaust manfolds. Revved upto about 2000 for a minute then sprayed the maifolds WD40 gone instantly from all ports apart from No5 which stayed wet.

So swapped No3 and No5 htleads and plugs No5 remains wet.

Swapped injectors No3 and No5 number No5 still remains wet.

If injector plugs are pulled at idle speed drop on 5 is same as the rest. Im confused.

While revving and squirting manifolds I thought I could hear the odd (not continuous) harsh mechanical "clack" on the LH side of the engine, but hard to tell with all the general racket, popping air cleaner and probably popping in the exhaust.

So I next is rocker covers off and check valve opening? Not today though this is an outside job and its chucking snow down now.

Thanks

Mike

[Hybrid_From_Hell]

Try new plug in 5

Nige

[MikeAK]

Hi again,

Tried a brand new plug in No5 tonight, made no difference.

So pulled LH rocker cover and checked valves opening. All looked about the same. Measured on No5 EX with steel rule from spring cap to cylinder head lift is approx 5.5mm. Checked a couple of others and they are about the same.

So if its not the plug, ht lead, injector or cam what is it?

Any more ideas very welcome!

Thanks

Mike

[Hybrid_From_Hell]

What make )ie genuine or pattern) are the Dizzy cap rotor arm and plug leads ?

And how old

Nige

[Henry Webster]

Whilst your under the dizzy cap have a look to see whether there is any play in the rotor arm contact. If in doubt change it for a genuine LR bagged Lucas one. Much more expensive than the aftermarket Lucas version, but much better quality.

[MikeAK]

Dizzy cap and rotor arm genuine, approx 6-7 months old. HT leads Bosch pattern set, same age.

Will swap complete Dizzy cap, rotor arm and leads from my 3.9 tomorrow see if that makes any difference.

Mike

[David Wright]

Possibly leaking head gasket allowing coolant into the cylinder - mine was on No1 cylinder

[paintman]

That would tie in with the 'runs for a while then goes wrong'. Pressure builds up in coolant system & then water is forced into the cylinder.

Any known coolant issues with the car?

Have you tried putting a plug on the suspect cylinder lead & earthing it to the block to see if you get a spark when the engine is running?

Unplugging the injectors won't make much difference as they aren't directly related to a particular cylinder & just inject fuel into the manifold as a bank of 4 (all 4 fire simultaneously) on alternate sides.

[MikeAK]

Hi,

No known cooling/overheating problems. When the fault started had been driven some distance and there was no pressurising or water loss. Since I started looking at it has not used any water.

Won't be looking at this tonight, its snowing again. Will post back when I've tried the dizzy cap etc off mine.

I think removing injector plugs is valid to find a low power cylinder. I know the're bank fired but the injectors are at the end of the intake runners pointing at the valves so one cylinder doesn't "see" the fuel for another.

Mike

[MikeAK]

Back again,

I think people may have missunderstood the problem. I doesn't run for a while then go wrong, It was fine then over about 10 miles started to misfire now it misfires permanently.

I managed to have another quick look at this this morning before seting off for work. When pushing on the pushrod side of the rockers they feel absolutly solid. I would have thought after not being run for over 24hrs followers would have leaked down a bit. Measured the height of the valve spring caps above the cylinder head on No5 then pulled rockershaft off. Inlet on No5 was then 0.2mm higher so must have been held slightly open. The follower was definatly on the back of the cam when this was measured. That would account for popping back in air cleaner.

I will check all valves tonight (weather permitting). I have read that if oil pressure is to high (stuck relief valve) followers will "pump up". Would that account for the rev limiter effect, as engine is revved up oil pressure increases and valves stop closing properly?

So what to do next? I think the options are put it back together run it and check oil pressure or as the plenum and rockers are already off pull the inlet, extract the followers and check for seized ones.

Or any other suggestions please!

Thanks

Mike

[Hybrid_From_Hell]

Compression test the engine

Nige

[MikeAK]

Right done the compression test.

Results (PSI)

1 160

2 162

3 150

4 168

5 165

6 158

7 165

8 150

Done with engine cold and throttle wide open all plugs out.

Was done with the rocker covers off so I could see what the valves were doing. 5 exhaust and 4 inlet are now opening much less than the others and less than they were this morning. I left it this morning with 5 ex on the peak of the cam so maybe it has leaked down? I think from the firing order that 6 in would be on the cam as well? Should they pump back up at cranking speed oil pressure?

Result - I'm more confused than ever!

Thanks

Mike

[Hybrid_From_Hell]

Compressions are okish, tad low all around but prob mileage

So, options are I think more a spark issue or a fuel issue

Have you gone right through the diag I shoved in tech forum ?

Things like you have that have plagued me over the years apart

from what been stated - and doesn't show up in tests are :

Amplifier on Dizzy either fialing or bad connection

poor eartyhs esp on heads and chassis

air leaks split hoes etc

failing coil

bad connections AFM injetors etc, remove plugs sctach pins with file tweak and refit

Failing the above when I have a moment I'll think and re read threrad but do the above

and report back

Nige

[MikeAK]

Thanks Nige

When I did the hotwire diagnostic I didn't do the power and relay tests as its obviously powered up and the fuel pressure is correct so pump must be running. Do you think its worth doing these? I did do all the sensor and injector resistance checks, throttle pot voltage checks and AFM voltage checks. All check out OK.

Have already checked for split/perished hoses etc.

Will clean and check all the earths and try swapping the coil, don't have a spare ignition amp but will see if I can borrow one.

I'm working away tomorrow and maybe Friday so will proably be weekend before I can do above. So I haven't lost interest if I don't post for a few days.

I'll be back...

Mike

[MikeAK]

Tried the suggestions in previous post today but no difference.

So decided it must be mechanical and pulled the inlet manifold. Its the camshaft

Inlet on 5 and exhaust on 6 very worn, 5 almost no lobe at all. Thats pobably why 5 showed up on Nige's WD40 test, couldn't have been pulling in much air/fuel at all.

The wear on this on is strange. I've had a few of these before and the cam has always been worn but smooth and the followers have been dished but smooth. On this one the followers aren't dished at all but have bits of cam stuck to them where its "picked up" and the cam lobes are heavily scored. Other lobes and followers have no wear. It as if the affected lobes have run without oil, that might explain the the sudden failure of a few miles. The others I've had have failed gradually over many weeks or months.

How are the lobes lubricated, is it just what runs past the followers? I want to check the oilways before I fit a new cam.

Anyway new cam and followers on order.

Whats the bedding in procedure for the cam? I seem to recall somthing like 2000rpm for 20 mins but RAVE just says fast idle till follower noise disappears.

Thanks

Mike

[Quagmire]

Not below 2000rpm for 20mins. No idling at all!!!!!!

Use lots of cam lube during assembly.

[Quagmire]

...and make sure you change followers too. New cam + old followers = swarf.

[MikeAK]

Thanks for the info. Followers ordered with cam. Cam Lube on its way as well now. Hopefully be running this weekend.

Mike

[Bull Bar Cowboy]

Thanks for the info. Followers ordered with cam. Cam Lube on its way as well now. Hopefully be running this weekend.

Mike

Mike, go easy on the four long bolts on the timing cover that secure the cover to the block water jacket ......... they have a habit of seizing an then shear ........ a little heat and gentle easing forwards/backwards usually does the trick ........ ifs its run 50% coolant all its life then they will be OK.

Also you will need a new timing chain & cogs ……. The old OEM chain will be stretched beyond belief ……….

[MikeAK]

Not going well, job stopped

When refitting sprocket retaining bolt it didn't fit!

According to microcat it should be 7/16UNF but the one from the old cam is 10mm!

Sod all chance of getting a 7/16UNF bolt round here at 3:00pm on Saturday so stopped till next week.

Did LR make cams with different threads?

Mike