I knew i'd need to replace the P38's exhaust ever since buying it. It failed its first MOT on major exhaust leaks from a hole in the rear box and a big leak from the flange between the downpipe and midbox. I'd stuck some epoxy putty on there to get it thru the test and started looking for replacement bits.

I wanted stainless and cheap. Not an easy combo. Kept my eye on ebay and found this:

Not ideal being straight piped, but cheap at 50quid and despite the listing not mentioning it, looked like stainless steel. So took a punt.

It arrived and seemed fine, so i decided to sort it out with a silencer. I had a stainless mid box that i'd removed from my brothers 320d BMW when he upgraded the exhaust, and figured it would fit nicely.

Removed old the rear box, it literally fell to bits:

Then dug the small silencer box out the garage and welded it into the rear of the new exhaust, had it on and off the car about 6 times getting the alignment right, but got there in the end:

I also had a nice tailpipe from an Audi A6, so carefully aligned and welded that on:

Having got to this stage i had a working back box and was quite pleased, but the mid box needed attention. The front flange was leaking, and there was a hole rusted thru it beside the hanger, which had got much worse with all the hacking about thus far.

I decided to get a bit silly, and so used a bit of the old backbox pipe, to create a streight thru mid box. I plated over the hole in beside the hanger with some scrap steel (not shown in this pic, you can still see the hole):

Having examined the front flange, i realised it was leaking because the round part on the downpipe side had crumbled away. After scratching my head i found an Audi exhaust clamp in the garage. These are nice, as they're designed to sleeve over the pipe and clamp on. So i cut the remains of the busted front flange off and set about figuring out how i can use the clamp.

The clamp was designed for 65mm pipe, but the downpipe was 55 and the silencer was 60. Luckily i had some pipe kicking around so sleeved the box and downpipe up to 2.5" to accept the clamp.

I didnt get it fully finished, as i took the backbox back off to paint up the welds to protect them, and proceeded to drop the damn thing on the ground and get the wet paint covered in mud.

So maybe tonight i'll repaint it and get the backbox re-hung.

It is LOUD. I only took it for a quick spin around the block, and that was also before i fixed the leaks. As expected really, my plan is to get a stainless mid-box for it as well, so i'll have it apart again at some point to sort that out, and that will make it somewhat more sensible. In the mean time i figured i'd enjoy a bit of V8 roar!

lockup and stall are different things.

The 1800rpm "slipping the clutch" feeling is the TC sitting against its stall speed. However the stall speed varies a bit depending on torque input and thus throttle position. Higher torque, means a higher stall speed, simply due to the fluid mechanics inside the converter. The throttle position also determines wether the trans holds onto the gear your in, and thus lets the engine rev up beyond the stall, or upshifts.

If your below the stall speed, and apply some throttle, the engine will tend to rev up to the stall speed and sit there. This effect boosts torque output, as a) the engines spinning faster and thus able to produce more torque anyway, and b) the slip in the converter gets used to amplify the torque further. Once speed in gear matches the stall speed, the engine revs will start to rise like a manual box. At light throttle, the box will shift before or just as that happens i suspect, and thus you'll find the revs just sort of sit around 1800 while it accellerates thru the gears.

The 4.0 and 4.6's also have (i believe) different converters with different stall speeds. From memory, the 4.0 stalls higher, to extract more performance from the engine. The larger 4.6 engine stalls out sooner, making it more refined. The diesels are probably different again to due the differing power band. Given these are old cars, its possible ones had the transmission changed and a different TC fitted?

The lockup clutch usually only kicks in in higher gears, and completely locks the converter solid, like a clutch on a manual car. This improves fuel efficency by removing the losses in the TC's hydraulic coupling. Newer boxes (like the modern 7/8 speed jobs) i think can use the lockup cluch more often, but the older ones like the P38's tended to only lock up in top gear at a certain speed.

Thanks.

I've got 10mm hose from the evaporator to the filter already. Its an 11mm filter, and i've got 11mm hose from there to the rails. I guess the 11mm hose will stretch onto the 12mm barb just fine, so i'll get the 12mm rails and T piece thing.

The LPGShop Valtek rails appear to have 5mm hose outlets, i'll email them and see if they can swap them for 4mm, but again i suspect the 4mm hose will squeeze on.

Will report back once the stuff arrives!
Cheers

I've replaced all the pipework already, did when i had the manifold off as some of the hoses looked a bit worn out. :)

phew thats good then :)

Had that bloody manifold far too many times already!

upload pics to imgur then paste the link

Quick one. I'm going to order a pair of the valtek rails and the diagnostic cable.

But before i do, am i going to have to pull the manifold off again and replace the nozzle things, or can i retain the bigas nozzle things and just swap the injector rail out?

Ok so managed to get the pipes connected up today and try things out.

Using nanocom, i started the engine on petrol and viewed the long term trim, which was showing as -35.

I started the engine on petrol and let it warm up, and the short term trims were fairly low. bank 1 was oscillating around zero, the other a little more negative, say -5 to -1 sorta range. I'd say the trims looked fine, while on petrol.

Then i switched over to gas.

After it stalling the first time (empty pipes i presume?) i restarted and switched over again and this time it switched fine. But the engine note immediately changed and there was a pronounced vibration and roughness from the engine. The fuel trims also seemed to swing in opposite directions. Bank 1 went from oscillating around 0 upto maybe +15-17ish. Bank 2 seemed to get more negative, but only a little bit.

So clearly something aint right, and given its different from one bank to the other i presume we can say its probably an injector issue? If it was system calibration then it would affect the whole engine the same way right?

Is there any other diagnostics i should look at, or should i just bite the bullet and buy some new injectors?

Thanks, thats helpful. So essentially, raising the gas pressure from 1.2 to 1.6 to compensate for the smaller injector nozzle.

yeh i think they're both nominally "200cc" injectors, which is why they're sold as a replacement/upgrade for the GEMS ones.

When i last checked the long term fuel trims it was sitting at -10 on both banks. I've done a few more miles since then though, so i'll recheck at some point and see if its stayed there. If its sticking around -10 then it suggests the new ones are a wee bit larger.

When i got it, the engine would barely run. I've replaced the MAF, both lambdas and the fuel injectors and finally have an engine that mostly works as it should on petrol. Hence now looking to get the LPG back up and running.

Once i get the LPG back online, i can compare the trims between gas and petrol and see if they look sane. If they're miles out or uneven between banks i guess thats a sign that the injectors are needing replaced? At least these V30's are nice and cheap. I may well just replace them anyway, but a few other bits need fixing first!

Well if your passing by can always ping me a message and see if it happens to line up. If i'm over glasgow way i can always give you a shout! :)

Thanks.

I guess i'll pipe up the existing ones and see what happens.

I presume the computer software and leads are readily available? How would i know what i'd need the reducer pressure to be at?

The new petrol injectors i fitted probably have a slightly different flow rate anyway (they're bosch Gen3's from a 1.4L K series), so the LPG calibration might well need a tweak regardless.

Had a look at the bigas rails last night.

Both had "3.0" stamped on the underside. I'm not sure if that suggests they're running 3.0mm nozzles, or is something else?

That might be handy, i'm right on the A92 in Glenrothes, so literally driving right past me if you take the scenic route to dundee.

Where about are you based? I work in Loanhead which might be closer?

Pulled the rears apart tonight.

Again the disks look new, pads are TRW brand so no crap been used. The NSR caliper is new, but the bottom slider pin was siezed quite badly. managed to free it off, got it all lubed up and working and rebuilt.

Offside caliper wasnt new but piston did move with some persuasion. again disks and pads all good, and again the bottom slider pin was a bit stiff though not as bad as the other side. Oddly when i took that one apart it was seriously pitted and corroded, so i'll get a new slider for that side.

Is there any forum members local to me (fife, scotland)? Be useful to have a go in another P38 to compare!

Stripped the front brakes today and had a look. Everything was clean and free. Pistons all moved easily, silders free and pads moved easily in the carrier. Pads are Mintex brand. Disks look pretty good as well, no pitting or corrosion.

Will check the rears as well maybe tomorrow.

I did notice the ball joint on the drivers side track rod was fubar, boot has split and its all rusty inside, so that needs sorted!

Thanks for the info. They do an 11mm filter instead of 12, so i guess i'll get one of those and hope the pipes squeeze on!

I was actually already thinking about the possibility the injectors were iffy. Also have been run without filter might have clogged them up etc?

There was a note from the last LPG service about "fluttering" injectors on one bank, which seems to have been fobbed off with "ignore until it gets worse". Interestingly its the same bank that was fouling plugs on petrol so maybe more going on than meets the eye.

Is there an easy way to check nozzle size? I will have a look thru the installation paperwork and see if its mentioned in there.

yeh i guessed it was pressure equalisation.

I will fire an email to lpgshop and ask them if they're connected internally.

So while trying to make the car actually run, i pulled all the LPG pipework out the engine bay.

The injectors were originally mounted above the exhaust manifolds which was stupid, so on reassembly i remounted them off the plenum.

The pipework from the evaporator was strange so i removed all that and want to re-do it properly. there was also no filter.

So i currently have this:

Originally there was two short pipes off each side of the evaporator, each running to a Y connector. One branch of the Y went to a gas rail, and the other linked to the other Y.

I understand i should have a filter, and i've discovered filters with two inlets:

http://www.lpgshop.co.uk/lpg-filter-h-inlet-2x12mm-outlet-2x12mm/

So instead of all the messing with Y pieces, can i just run the two evaporator outputs into that, and then run the outputs from that directly to each gas rail?

perhaps the brake pump?

not thrashing it particularly. One blast off a roundabout (full throttle from 30ish upto about 70), otherwise just sat on the motorway doing 70-75 indicated, bar a stretch of 40mph average cameras thru some roadworks. There was a bit of traffic on the way home, but that didnt seem to effect it too much (average on way in showed 14.7, and 15.1 on the way back)

Oddly, the front wheels arent balanced (the tyres were fitted in a rush by the guy i bought the wheels from), the rear tyres were ruined, so i bought some part worns and had them fitted by a local respectable garage and they appeared to be balanced up as you'd expect.

So unless it is a front and its just not detectable due to slack in the steering or something, it seems a bit odd.

I want to get underneath and check/grease the propshafts, who knows when they were last done.