Tried a 7'x4' unbraked trailer today, loaded with logs. Towed smooth as silk, wouldnt even know it was there.

Even over the really rough bit of road after the Queensferry crossing that had the whole car jiggling with the big trailer, there was only the slightest of vibrations. None of the horrible banging and clattering the big trailer does either.

Will be picking it up again later in the week unloaded, so be interesting to see how that compares.

Gilbertd wrote:

Or if it isn't going to be linear you should be able to work out the curve from a Bosch one. This does assume you have one that is working so you can read the airflow and measure the voltage.

Yeah, my plan was just to connect them both up to the engine in series and log the output from both. Since we know the Bosch curve, we can plot the curve for the SAGEM unit. But ofcourse, that only gives you useful data if both MAF's are actually working correctly.

Bosch Motronic ECU's have a 512x1 lookup table which contains voltage against airflow. Its pretty easy to extract it if you have a good definition file for the ECU. The SAGEM must surely be the same, but there doesnt seem to be many folk that have put the effort in to these ECU's.

Its almost never linear unfortunately. They tend to design them with much more resolution at lower engine speeds. so the curve ends up exponential.

heres a few bosch curves for instance:

So i'd like to do the gaskets and i'd like some pointers.

I want to use quality parts, i hate shite that doesnt work properly and ends up meaning i have to redo the job.

I've seen the likes of this:
https://www.turnerengineering.co.uk/stc-4082-v8-gasket-set-top-c2x20634423
Turners have a good name, so i'm hoping this is a decent kit, but anyone know?

Is it worth looking into any of the aftermarket upgraded bits like Cometic Gaskets or ARP head bolts? Most modern engines use MLS gaskets so they're clearly superior, but do they work properly on an old thing like this?

I also need to reseal the front timing cover and fit a new alloy sump pan, any gotchas here?

Also pondering, do i pull the engine out the car? or is it okay in situ?

I've been thru a few MAF's, they're impossible to buy new, and copy ones are junk. I was tempted to try and datalog airflow against voltage, and figure out an adaptor to run a modern Bosch MAF on it.

I can easily acquire the voltage/airflow curves for a Bosch MAF, but the Sagem/GEMS MAF seems impossible to find, and ofcourse datalogging a broken one gives you useless data, so i've never bothered going any further. Someone who can tune the GEMS should be able to pull the airflow table out of the stock ECU, but i've never managed to find anyone willing to actually do it.

However the one i'm using now seems alright.

i suspect this job is going to snowball 😂

okay so as one might have expected in hindsight, the brake override doesnt actually stay enabled once you start driving. Its spring loaded in such a way that it pops out again.

I did notice very visible pitching of the trailer on the motorway, the nose of the trailer bouncing up and down with a very close correlation to the jiggling the car is experiencing.

So i guess we're back to the original question, is it simply too much play in the hitch/coupling allowing the trailer to bounce around at a high frequency. A new hitch is £320 which feels like a lot of money if it doesnt fix it, although to be fair, it probably needs it regardless. Its more that it might be better to sell this trailer and buy something better instead of spending the money on this one.

I wonder this about mine. Its really flat at low RPM's and only really wakes up above 3k or so. Given its a big torquey V8 that doesnt particularly like to rev it seems a bit "upside down".

I want to change the headgaskets soon as i suspect ones a bit leaky, perhaps thats a good time to check the cam, however is there any easy way to check for wear, or am i going to have to remove it and carefully measure everything?

Yeah the roads certainly play a part, theres a stretch of newish road right after the queensferry crossing which was REALLY bad, and the amplitude massively reduced as soon as i was off that new section and back onto the original tar. However its also doing it, albeit to a lesser extent on all roads. I suspect its perhaps a few factors working together, play in some components and vibrations from the road surface setting up a bit of resonance or oscillation, and perhaps the rear shocks are getting a little tired and are struggling to damp the faster movements.

I've loaded a car at the weekend that i'll be taking to the scrappy at some point this week, so i'm going to try the return leg with the brake override enabled and see what happens.

Is there any gotchas swapping out an electric interior for a manual one?

Dont particularly care about the electrics and may have found one in a preferred color which is manual

From dealing with Bosch Motronic ME7.5 its maybe worth pointing out that the cruise control routine has gear ratio inputs. Each gear is programmed as an allowable ratio between engine and road speed. If the engine speed and road speed dont match up, cruise wont engage. I presume this is so wheelspin or clutch slip or whatever causes the cruise to get disengaged.

I ran into this issue when i swapped a Audi TT ECU into my Audi A4. Different gearbox, different set of ratios, and cruise wouldnt work in certain gears, but would in others. Most annoyingly, it wouldnt work in 5th. I eventually fixed it by altering the actual map in the ECU to correct the allowed ratio values. It took bloody ages to sort out as well, as i didnt have the map location in the definition file, and ended up finding snips of information, had to decompile the rom, find a matching code snippet to get the address pointer to the correct table and then do some data logging in each gear to figure out what the correct values should be.

I presume this is a Bosch ECU from a similar era, so i would assume it has similar routines. You could try fiddling the road speed input into the ECU and see if you can get it into a speed range that the ECU is happy with?

Can these clips be added easily? I noticed on mine, the mats themselves had holes, which look like the middle part in the pic above, but theres nothing in the carpet for them to clip to, nor any locking piece.

I've suspected the rear diff for a while, when i got it, it was noisey on overrun at motorway speeds. That noise has either gone away or i've stopped noticing. I also changed the oil at one point and it was properly black and burnt looking, whereas the oil in the front diff looked nice and clean.

Still, investigation required. In particular the propshafts as if those fail it could get messy!

brake pads i thought about at the time, gently touching the brakes didnt seem to alter the noise though, and braking harder it would go away.

I'll need to get underneath and check the propshafts i guess!

Had the p38 out for a long drive today. At one point in roadworks doing about 40mph I noticed a pretty worrying noise.

Sounded like a rubbing or scraping sound from the rear axle or something around there. Most noticeable when holding the throttle at cruise. Full over run or acceleration seemed to make it go away or at least become much less noticeable. At higher speeds I couldn't really hear it any more.

I also have a clonk noise when changing drive direction, eg shifting from reverse to drive, most noticeable at low speeds, which might be related?

Any ideas where I should be looking?

Not sure if theres an override actually, i'll have a look.

Its fairly standard cable operated drum brakes.

had a look over it this evening, and certainly to the eye, i cant see anything wrong with the wheels.

Bearings all feel fine, no play, no roughness or odd noises. Spun the wheels by hand and theres no obvious flat spots or egg shaped running.

They are dated 2014 though. I bought new wheels and tyres as a package back then, as the original wheels were needing refurbed and it was cheaper to just replace the whole lot.

Thanks, i think they are 13". Hopefully at some point this week i'll get it jacked up and check the tyres and bearings.

Is it worth trying to have the wheels balanced?

Mines on Michelin Pilot Sport 4's and doesn't exhibit any weirdness despite it being a very modern tyre design.

I guess it depends if you actually need an all terrain tyre. Mine spends basically 99% of its life on tarmac, and I'm not up for ruining that handling in exchange for some off-road grip I use once in a blue moon!

I've done some very light offroading with the Michelin's and it was fine, I doubt they'd deal with mud ofcourse.

Thanks for the pointers. The tyres arent ancient, i replaced them all when i bought the trailer, but yeah they could have deformed or something. I'll check the date codes.

The trailer itself doesnt have any branding on it, it appears to have been built probably 25-30 years ago. It all looks fairly DIY, but done properly with solid steel sections, proper 5 stud trailer wheels with load rated tyres and a nice bradley hitch. The original wheel rims were dated 1989. The hitch is dated 1997. I've replaced a few of the steel crossmembers over the years, mostly because it was C channel and had been torn by the previous owner ratchet strapping things to the leading edges.

I wouldnt even say its a progressive change. It was fine, then it wasnt, and its been equally bad the last few times i've had it out. Like i say, its never been nice to tow empty, but this vertical jiggling motion is very much new and moves it from a bit "uncomfortable" to basically being unusuable for anything more than a short local trip.

I guess i'll start with the wheels/tyres and check all the bearings etc. Costs nothing.

Tyre pressures are something that hasnt changed much, they're at about 60psi, sidewall recommends 90 for the full 3 tonnes, but Most inflators wont go that high though. I think i had them around 75 at one point but they've slowly crept downwards over the years and are now around 60, which feels like "enough" for a typical saloon car on the back.

I'm just a bit loathed to spend £300 on a new Bradley HU12 to find its still just as bad afterwards!