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CATALYSTS · V6.24
The XM shares with the Peugeot 605 the last PRVs of the PSA group: the 167-170 bhp 12-valve ZPJ, then — from 1990 — the 24-valve ZPJ4 and its ACAV variable-geometry intake, 200 bhp without any turbo, on the V6.24. And a special case: the S6A, the 12-valve V6 to 15-04 standards for export — identical to the ZPJ, only the engine number changes.
The ZPJ — SFZ in the type approval — is the 12-valve 3.0-litre with Fenix 3B injection; the ZPJ4 — SKZ — is PSA's own 24-valve, with its heads, its sequential Fenix 4 injection and its ACAV intake. Same code on both sides of the group: the Peugeot 605 gets both. The S6A is not a third engine: Technical Note no. 4 is categorical, it is identical to the ZPJ.
On the V6.24, each head has its own « 6 into 1 » sheet-steel manifold with a Metex ball joint, and each bank its own oxygen sensor + catalyst assembly. The front bank's line being longer, a small light-off catalyst placed under the engine pre-treats its gases, so that the two main catalysts work at the same temperature. The ACAV intake, for its part, plays in three configurations according to revs and throttle position: half-volumes separated at idle — torque configuration —, connected between 4,000 and 5,000 rpm, joined above — power configuration.
Technical Note no. 23 (V6.24) and Technical Note no. 4 (S6A) are in the Library, with the two Pub et Trade workshop sheets; the 24-valve is explained in detail on the ZPJ4 file.
The XM and the Peugeot 605 share both engines, code for code — 12-valve ZPJ, 24-valve ZPJ4 — and their workshop sheets answer each other. The XM stays at 12 valves while the Safrane and the A610 do too; it goes to 24 when the 605 SV24 does, in 1990.
The XM V6 to 15-04 standards takes exactly the same spark plug as the Renault Safrane — RFC 58 LS3 — but with a 1 ± 0.1 mm gap and 1.5 m.daN torque, where the Renault manual asks for 1.2 mm and 2.5 to 3 daN.m. Each manual applies to ITS car.
The same ZPJ4, twin-turbocharged by EIA, reaches 408 bhp in the Venturi 400 GT — the most powerful PRV road car in history. Only three road cars have a 24-valve PRV: the XM V6.24, the 605 SV24 and the 400 GT.
From 1997, a 60° « PR » V6 — ES9 at Peugeot, L7X at Renault — succeeds the PRV on the XM and 605. That engine is not a PRV: only the ZPJ, S6A and « early » ZPJ4 versions belong here.
Eight answers drawn from Citroën Technical Notes no. 4 and no. 23 and the workshop sheets — the FAQ has dozens on the XM.
The two workshop sheets and the two Citroën Technical Notes, readable page by page: XM V6 3-litre injection (ZPJ/SFZ) — Pub et Trade sheet · XM V6.24 (ZPJ4/SKZ) — Pub et Trade sheet · Citroën Technical Note no. 4 — XM V6 S6A, 15-04 standards · Citroën Technical Note no. 23 — XM V6.24
The XM has its own section on the forum — presentations, restorations, questions to members who drive one. Citroën XM section →
The 24-valve ZPJ4 and its ACAV intake, explained in detail — the 12-valve ZPJ — and the 605 that shares everything.