Delta S4 - Water Pump
This particular S4 had spent most of its life in two separate collections, interspersed with a thorough refresh by the Baldi Twin’s in 2011. It was in beautiful condition, but was suffering from lack of use and regular maintenance.
One issue was a slow but steady coolant leak from the back of the car once it was hot. Diagnosis proved difficult, with much use of an endoscope to try and locate the leak, which disappeared when the car was cold. “Please don’t let it be the water pump seal” we said. It was the water pump seal, confirmed by evidence of staining from the seal housing tell-tale hole.
Removing the water pump to investigate further is not the work of 5 minutes. Access is not great and many other things had to be removed to gain access. With the pump on the bench it was obvious that the pump seal had been leaking for some time. Static seal availability didn’t look great and we were quoted €12,500 for a NoS pump, which seemed ridiculously expensive even by group B standards.
Stripping such a rare part it always approached with patience and caution, as mistakes are not really an option. Once the pump was apart the static seal face looked ok, but the expanding rubber section of said seal was almost impossible to inspect, so remained a suspect. The seal face on the back of the impeller looked less good, however.
This rotating seal face is actually a part of a steel boss, which the cast aluminium impeller is screwed onto and then dowelled into place. Some very cautious and exploratory attempts at removing the dowels confirmed that the boss wasn’t coming out of the impeller without a high risk of damage to both – not an option.
Several phone calls later and Lapping Services Ltd in Hinckley were confident they could help restore the rotating seal face despite the fact it was recessed from the back of the impeller, so an appointment was made to go and see them.
In between times, we managed to source a NoS static seal, which it turns out Lancia borrowed from another in-period Fiat Group vehicle.
Followed by topcoat:
Lapping Services inspected both the new static seal and the impeller seal face, and tested both for flatness on a very special machine. This revealed that the surface of the impeller seal face looked like the surface of the moon at a micron level, having 3x 60 micron low spots at 120 degrees apart, and the static seal face was also 40-micron out of flat.
They patiently made up a tool so they could hand lap the impeller seal face back to flat, which took 4 hours, and they quickly got the static seal face into good shape on one of their lapping machines. After this, the combined error across the two seal elements was 7 microns, which is probably better than it ever was when new.
New bearings were relatively easy to source, and making new gaskets and rebuilding the pump took about 3 hours.
Given the time taken to refit it to the car, we wanted to test it before we refitted it, so we made up a simple fluid loop, filled it with coolant, pressurised it to 20psi and ran the pump via a drill for 15 mins to check all was ok.
It was, so we fitted it back on the car and the problem was solved. Total costs for the parts and specialist lapping services was circa £500, which was a massive saving Vs the quoted €12,500 for a NoS pump, which might not have been in any better condition.
Delta S4 - Fuel System
Although based on work done on an S4, this is typical of the sort of generic issues found on older cars, especially those in collections which aren’t used much, therefore often don’t get specialist inspections or maintenance. The fuel system design on the S4 Stradale is a little different to other Group B homologation cars in that, whilst it is bespoke, almost all of it would go in the bin if the car was upgraded to Corse spec, which is not necessarily the case for say an RS200. It has two Bosch 044 pumps, each pulling directly from a fuel tank via an inline filter, which is not ideal, and then feeding a strangely designed and very flimsy swirl pot, which was clearly an afterthought as it doesn’t feature in the parts manual. From there fuel is fed to a beautifully made, Stadale-specific, fuel rail which features the same type of Webber fuel pressure regulator as early Sierra Cosworths, F40’s, etc used in period.
All of this is joined together with rubber fuel hose and jubilee clips. Now bear in mind that a single Bosch 044 moves a lot of fuel, can generate 8-10 bar against a dead end and can easily support 500bhp, then two of these feeding a 350bhp car is serious overkill and causes a vast amount of fuel to be moved around, which mostly just generates heat. Add in that all of these rubber hoses are now 40 years old and more like plastic than rubber, and that Webber fuel pressure regulators from this period have a known failure point as they age (the gasket in the half joint shrinks, reducing the clamping force on the crimped joint), and you have the perfect ingredients for a very serious fire event. Sadly, an S4 Stradale succumbed to exactly this kind of event in 2025, which is heartbreaking. At the very minimum, on a car of this age all fuel hoses need to be replaced and old tired jubilee clips should be replaced with proper fuel hose clamps. It’s also essential to change out fuel pressure regulators of this type for a new one. The Webber ones are NLA so on this particular car we used a Webcon supplied equivalent. This still leaves the issue of the two small sections of 40 year old fuel hose crimped directly to the fuel rail, which could be replaced and hose clipped back on, but we eventually decided to go a different way.
The below pictures show what comes out of two 15 year old fuel filters when a car has spent 99% of its time sat still. This is dried up fuel varnish – no wonder it wouldn’t start!
We also found this modified fitting on the discharge of both 044’s – quite scary given the barbs are there to help keep the hose on!!!
We replaced the existing rubber hoses with new, swapped old jubilee’s for new clamps and had to resort to aftermarket filters to replace the NLA existing items, and this got the car running. But given the overall system design, the fact that there was evidence of a fuel leak from the flimsy OEM swirl pot, which stubbornly refused to reveal itself on a pressure test, and the 40 year old sections of fuel hose that were an integral part of the fuel rail, we elected to redesign the system from scratch.
The brief was to make everything reversible if it was ever required, but this instance overall safety meant the concept of originality was relegated to being stored in a box in the loft.
The two 044’s were replaced with Facet RedTop LP lift pumps, which fed a purpose designed, 2mm thick, 1.5Ltr swirl pot, which picked up the existing swirl pot mounting holes.
This fed a single 200 series Bosch HP pump via a 100 micron rebuildable filter to a Corse type fuel rail made for us by Geoff Page Engineering.
This was all piped up using Goodridge G-Line 910 XF hose and 811 series fittings. The electrical install was modified to allow the HP and both LP fuel pumps to be controlled as before but fused separately (the stock design has the 2x 044’s sharing a common fuse!).
The resulting install looks OEM to a point that only an S4 expert would notice it was different, uses all the original chassis mounting points to fix and is 100 reversible should there ever be a need to go back to stock. This set up is in accordance with current motorsport standards and should remove a significant risk of fire from what is now a very rare and valuable car, making regular use a less nerve racking experience!
Delta S4 - Steering Rack
This car had a soft but noticeable clunk through the steering wheel when you applied lock. A poke around and some diagnosis quickly pointed to the rack bushes themselves – not the ones that isolate the rack housing form the chassis, but the ones the actual rack runs on within said housing. The PN in the official spares catalogue for these bushes is NLA, so as usual it’s back to detective work. The only thing to go off to start the search is the rack OD and some markings on the crumbled fragments of rack bush that were left. We’ll spare you the details of the hours of searching, but we managed to find what we believed was the correct part from another FIAT group car, which is not a surprise, although the rack assembly is branded as Abarth and is S4 Stradale specific.
To get what was left of the old bushes out was a rack out job, which like most things on an S4 is a bit of a struggle. One thing common to all group B homologation cars is that they were never really designed for normal dealer servicing, and most of what was on a road car would end up in the bin if it was upgraded for competition use, so little thought was given to accessibility and serviceability, hence why everything takes longer than it looks like it will.
We digress…. After a couple of hours the rack was on the bench.
Digressing again, the S4 Stadale rack is unusual in that it features Vacuum assistance, so it has quite an unusual pneumatic valving arrangement. Trying to find information on this led to the usual answer – you’re on your own – so we carefully set about stripping it down.
Getting the pinion out was a 2-day fight. It turns out that within the pinion housing is a spring-loaded floating piston, which operates the vacuum porting valve via a small pintle, and this piston has a rubber seal around it, which was very firmly stuck to the inside of the bore it ran in.
Eventually it succumbed, and the pinion assembly was free, thankfully without any damage, which allowed the rack to be removed from the casting. With everything cleaned up, the new bushes were fitted (and they did, perfectly) and the rack was reassembled once everything had been cleaned and inspected. It’s worth noting that within an S4 rack there are normal mechanical components and then there are rubber containing pneumatic/mechanical components, so using the right grease in the right place is hugely important on a safety critical component. Going back to the Vaccum assistance, the more I stared at it the more I got how I think it was supposed to work, but started to suspect that it actually couldn’t. I took the components in question to a good friend of mine in the same line of work who has a brilliant engineering mind, and he couldn’t work it out either. Was this set-up needed for homologation purposes but they didn’t have time to perfect it on the road car so found a way to nobble it so it was inactive? Stranger things have happened… Anyway, the rack was fitted back in the car, connected up with new vacuum hoses to replace the rock hard originals and it all operated smoothly. During this process I managed to find somebody who had an S4 Stradale rack for sale. I was never fully sure if it was new or not but he wanted £4.5k for it so it was a last resort. The parts to complete the above cost less than £50.