Help needed with power loss

[flyboy]

Hi guys,

I’m wondering if anyone can add some suggestions for me...

1998 P38 4.6

For the last year it’s been missing/losing power above 2500rpm. I was hoping it would get worse to make it easier to diagnose, but it hasn’t.
Most noticeable cruising on the freeway at 110, the tachometer needle starts dancing erratically with slight power loss (about 2500rpm) if I start to put my foot down further it develops a bit of a shudder, then by the time I have my foot on the floor it really carries on, missing and I can’t get the revs above 3000 with complete power loss.

I’ve plugged in the Nanocom and the fault is “0340 camshaft position circuit malfunction” if I clear it, it doesn’t come back until I get it to start missing etc..

Here’s what I’ve done...

New spark plugs and leads
New fuel filter
Tried another MAF with no change
Removed and inspected the camshaft and crankshaft sensors (both looked ok)

I guess the obvious is to buy a camshaft sensor, but just thought I’d ask on here for any advice before I start throwing parts at it.

[PeterH]

If the fault code is camshaft position sensor, I would be replacing that first.
Might be an intermittent fault, but sensors can develop problems with age.
If you don't know how old yours is, it's a good thing to replace as a first step.
At least you know that's good before you start looking elsewhere.

Crankshaft position sensors tend to be a showstopper when they die, mine failed going through a major roundabout on a busy road at peak hour, not fun!

[flyboy]

Thanks Peter,
I’m fairly sure both sensors are the original so after 23 years it might be worth replacing both!

On a further note, whilst replacing the vacuum tube for the cruise control, I noticed the PCV pipe was quite loose and soft. I’ve taken it off and it’s quite oily in there. I’ve googled a replacement and I think there is meant to be a spiral separator there? Is that something I should be able to see without removing the valve cover? If it is, I definitely don’t have one....

[flyboy]

Hang on....scrap that comment about no spiral separator...I was looking on the wrong side/pipe. The pcv pipe has been sucked flat though...so I’ll replace that pronto!

[PeterH]

I replaced the oil separator on mine recently, they can get very gunked up over time.
Once you have the hose removed, you need to be very patient, don't try and pull the seperator out in one go, it will be very brittle and break off easily.
Worst case you will have to remove the valve cover to get the broken bits out.
I used needle nose pliers, you have to gently wiggle it up and down, side to side, use WD40, carby cleaner or something similar to help it let go.
Keep at it, eventually it will start to move a little bit, after a while it will come loose and you can carefully pull it out.
Mine broke off at the top anyway, but I was still able to retrieve the rest without any dramas.
Hope that is of some help!

[zzsteve]

Look to the camshaft sensor and its connector first. I have had this same fault and luckily found the problem in the 3 pin corroded connector which is just accessible from under the vehicle on the front cover of the block.
HTH
Steve

[flyboy]

Thanks Peter,
I got the spiral out without breaking it and have cleaned it.
Zzsteve...I removed the cam sensor which was the source of one of my oil leaks since the o ring had turned to plastic. Connector looked fine though.
The positive thing is after I’ve fiddled with everything, the problem has gotten worse...so I must be onto something right. I’ve fiddled with so many things I’m not sure which one though!
I’ve got a new cam sensor on the way from the UK, so will report back once that’s in.

[flyboy]

Problem solved!

I put in the new camshaft sensor....no change and the fault came back.
I then put in the new crankshaft sensor...and noticed the old one had a slight mark on it where something has worn it away.

Took it for a test drive and wow! What a difference. I forgot how much power this thing had...now feels like a 2 tonne car instead of 5 tonnes. And running beautifully.
My only concern I guess is if the new one gets rubbed in the same spot there’s something not right, but at the moment I’ll just enjoy the difference.

Thanks guys for your help.
Photo of the damaged crankshaft sensor....

https://uploads.tapatalk-cdn.com/20210503/9ebb9999da5b7e829e4b64bbd2aabf39.jpg

[PeterH]

Nice one Marcus, glad you got it sorted!
Yes they are a joy to drive when they are running well.
I usually suspect a sensor fault first before looking elsewhere, they do tend to start playing up with age.

[Scouse]

I'd be removing the lower access panel from the front of the gearbox & checking the reluctor gear. My car broke down last year & wouldn't rev over 1800 without a great deal of effort. It would start fine with no faults logged. Eventually I noticed a mismatch between the revs on the tacho & the Nanocom and the catalysts getting extremely hot when persistently trying to get past 1800 which led me to check the crankshaft sensor.
My sensor was fine but the reluctor gear had become loose on it's rivets resulting in a fluctuating signal at 1800rpm which only got worse when trying to get past it.
Yours could well be the same if it's made contact with the sensor.

[flyboy]

Thanks Scouse,
Is the access panel obvious?
I’ll get under tomorrow and have a look...

[p38arover]

Is the access panel obvious?
I’ll get under tomorrow and have a look...

Yes. The half-moon shaped aluminium cover at the front of the bell housing.

170740
170741

Does the '98 P38A have the solid or fabricated reluctor ring? Probably fabricated like mine.

My '95 flywheel - note the repaired fingers that were damaged when they struck the crank position sensor. To the righ of them you can see the "missing tooth" which tells the system the start of the pulse train.

170737

The pulse train from my engine. Note the missing pulse near the left. Then, to the right, the shorter pulses from the damaged fingers (before repair). (Yes, I own a CRO or three. [bigwhistle] )

170739

Later flywheel:

170738

[Scouse]

GEMS has the fabricated (pressed/folded metal) type.

[zzsteve]

Thanks for the update Marcus and closing the loop. Glad to see it fixed and I appreciate Ron's (analog!) CRO traces.
How do we now interpret the "0340 camshaft sensor fault" though?

Cheers,
steve

[flyboy]

Just crawled underneath in the rain on the gravel driveway with all the wrong size spanners etc...
Took off the inspection plate and everything looks good in there...reluctor ring still firmly riveted and all teeth straight and clearing the sensor probe.
As for the camshaft sensor fault being the only fault, yet the crankshaft sensor being the issue I have no idea!

[flyboy]

Sorry guys....I’m back for more help [emoji30].
It seems my excitement in fixing it may have been premature....
After 24 hours of running perfectly, Now it still stumbles and coughs when cold and won’t go past 2000rpm (worse than before). As it warms up it improves and eventually it will rev all the way out, (better than before) but gives a bit of hesitation and misfire through about 3000rpm.

No faults being flagged on Nanocom.

When the rain stops I’ll pull out the crankshaft sensor and see if it has any marks again on it. If all looks fine, then I’m truly stumped [emoji848]

[flyboy]

Ok...I’m on to it...

My reluctor ring is missing an inner tooth!....not the one it’s meant to be missing. There’s an inner tooth that has very cleanly sheared off near one of the bolt holes. The outer tooth is still there.

Next step...I’m guessing the flex plate has to come out...is that something I can do or is it off to the mechanic?

[flyboy]

https://uploads.tapatalk-cdn.com/20210508/e1a99e4bb48985c95aca05a1e3455605.jpg

[Scouse]

Unless you can find someone very clever with a welder, it's a gearbox out job I'm afraid.

[flyboy]

Thanks Scouse,
I rang a few people and came to the same conclusion...
I’ve tracked down a good used reluctor ring/flex plate and it’s booked in to a transmission shop in 2 weeks...

[Scouse]

I hope the repair bill isn't too expensive for you.