Have people used the proper P38 diagnostics kit? Generic scanners dont work on these cars.

i went with 30 all round.

Dont get why the rear pressure should be so high? Maybe if its carrying lots of weight or something?

yeh too big and it ends up droning though. I quite like the rasp! Oddly it only does that when revving it in neutral. When driving its a much deeper noise. You can sort of hear it at the end, unfortunately the wife stopped the video right as i opened the throttle!

The rear pipe is 2.5", the midbox is 60mm, and the downpipe is much smaller with a really nasty Y collector on it. I will eventually replace the mid section with 2.5 to match the rear. The downpipe niggles at me at i really want to sort it properly with a decent collector thats not horribly restricted like the factory one, but its too much work for little gain i think.

It also still has cats, and i doubt we'll achieve maximum V8 noise with those still present, but i dont really want to take them out as its MOT/Emissions hassle i dont need.

My end goal is something civilised but with a distinct V8 note though. This is just an interim step for a bit of fun. Once i get a new middle box and figure out how i'm fitting it it should be a bit more sensible.

yeh its not quite muscle truck territory, but its pretty decent!

haha! Yeh, the other one i've seen with welding is folk cleaning parts with chlorinated brake cleaner. If theres any residue, when heated it turns to phosgene gas. I'm not sure the stuff we get here in the UK has tetrachloroethylene in it, but certainly in the US it comes in both flavours.

http://www.brewracingframes.com/safety-alert-brake-cleaner--phosgene-gas.html

Managed to get the backbox refitted earlier and fired it up. No leaks first time which was pleasing.Took a short video after a test drive:

https://www.youtube.com/watch?v=-LsUKMUO7XM&feature=youtu.be

The noise is interesting, from inside when driving its quite deep and boomy, but only when on the gas accelerating, cruising along is quite civilised. From outside when revving it, it sounds epic, like some sort of muscle car. Clearly its too much for daily use and it'll get fixed properly with a new centre box at some point, but it certainly puts a smile on my face :)

If we can end up with as much of the muscle car sound as possible, but just trim out a bit of the deep booming inside the car, that would be ideal. I suspect that dampening the deep boom will also kill some of the v8 rasp though :(

full stainless for £200 sounds bargainy, not found anything remotely close to that, was that new?!

Theres some on ebay for £250ish, but they're only mid/rear and only for dual silencer cars.

When i looked at the exhaust, the rear box was fairly small and is a straight thru design anyway. The middle box is huge and uses a reflection design where the gas bounces around and changes direction numerous times inside. As a result the general concensus seemed to be that the mid-box is doing most of the silencing, and is the one to change as it frees up the breathing as well. But then my rear fell apart anyway, so i figure i do both.

Exhaust place online has suggested a 6x15" box to replace the middle i think. Not sure if i weld it in myself, or pay someone to do it though. I've only got mild steel wire in the MIG (hence painting all the welds), and trying to sort the exhaust alignment on my own while laying under the car isnt easy!

I'll try to make a recording. I suspect it'll sound much worse on video than it does in real life, they often do! Camera phone mics just arent upto capturing such sounds!

First i need to finish reinstalling the backbox. I repainted it yesterday afternoon and left it to dry, but the wife was out in the evening and by the time i got the wee man to sleep it was too late to go start trying to fit the exhaust.

Just trying to decide how large a middle box to buy. I dont want to go too big and over-silence it again, but at the same time i dont want a sore head on the motorway!

both heaters are faulty anyway, so just feed it two new sensors and save the messing about!

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?