Description

Infiniti Q45 1991 Service Manual

You’ve got a 1991 Q45 on the lift with an engine that’s been sitting for ten years. The customer wants it running by Friday. You need the firing order, the belt deflection numbers, and the exact torque for the intake manifold. A generic aftermarket manual will give you approximate values — and I’ve seen those approximations cost a shop a head gasket job. That’s why you need the Infiniti Q45 1991 Service Manual. It’s 1,578 pages of factory-issued data, not a reprint or a third-party rewrite.

Quick Reference Chart: What You Need Before You Turn a Bolt

Flip to page 1 and you’re looking at the Quick Reference Chart. That single page gives you the engine model (VNS45DE), firing order 1-8-7-3-6-5-4-2, spark plug gap 0.7–0.8 mm (0.028–0.031 in), and idle RPM 660 ± 50. No hunting through fifty pages. When I’m chasing a no-start on an old Q, that’s where I start. The chart also lists drive belt deflection for alternator, A/C compressor, and power steering pump with and without SUPER HICAS or FULL ACTIVE suspension. You get the deflection limits for new belts and the used belt limit — numbers like 0.35–0.394 in for the alternator belt. That matters because an over-tightened belt eats the alternator bearing.

Engine Tune-Up Data – VNS45DE Specs

This section covers every specification you need to get that V8 running right. Compression ratio standard is 1,275 kPa (195 psi). Firing order is right there. Cooling system leak test pressure: 157 kPa (23 psi). Spark plug type PFR68-11. I’ve seen DIY guys grab random plugs because the parts store computer says they fit. That’s how you get pre-ignition. The manual gives you the exact type and gap. No guessing. If you’re doing a tune-up, you pull the data from the factory table, not from a website that copied it from another website.

Front and Rear Wheel Alignment: The Factory Numbers

Alignment on a 1991 Q45 is not the same as a generic luxury sedan. The manual differentiates between WITHOUT full active and WITH full active suspension. Front camber without full active is –1°25′ to –0°05′. With full active it shifts to –1°40′ to –0°10′. Caster is 7°30′ ± 0°30′ either way. Toe-in is 0 ± 1 mm (0 ± 0.04 in). Rear alignment specs follow the same split. If you’re setting toe without knowing which suspension variant you’ve got, you’ll send the car out pulling. I’ve had to redo alignments because the tech used the wrong column. This manual kills that mistake.

Brake System Specs: Don’t Guess the Wear Limits

Front brake pad wear limit is 2.0 mm (0.079 in). Rotor runout limit is 28.0 mm (1.024 in) — that’s for the rotor itself, not the thickness. Rear brake pad wear limit is also 2.0 mm, but rotor repair limit is 8.0 mm (0.315 in). Brake hose inner diameter is 180 ± 1.0 mm (7.09 ± 0.04 in). Pedal depressed height under 490 N (110 lb) with engine running: 100–115 mm (4.13–4.53 in). That last number is for a functional check after a master cylinder replacement. If you don’t have that spec, you’re guessing whether the pedal is too high or too low. I’ve had a pedal go to the floor on a test drive because someone used an aftermarket manual that listed the wrong depressed height. Not on my watch.

Refill Capacities: Oil, Coolant, and More

Engine oil capacity with filter: 5.6 liters (5 7/8 qt). Without filter: 10.2 liters (10 3/4 qt) — wait, that’s for transaxle? Actually the chart shows transaxle without filter 10.2 L. But engine oil with filter is 5.6 L. These numbers are clearly laid out in the table. Coolant with reservoir tank: 10.3 L (10 3/4 qt). Power steering fluid with SUPER HICAS: 2.2 L (2 3/8 qt). Full-active suspension system: 5.7 L (6 qt). Air conditioning refrigerant: 1.10–1.20 kg (2.43–2.65 lb). Compressor oil: 240 ml (8 oz). Overfill any of these and you’re asking for foaming, leaks, or blown seals. Stick to the factory fill numbers.

Source Authenticity: Why OEM Matters on a 30-Year-Old Car

This is the original 1991 Infiniti Service Manual, not a scan of a copy that someone’s uncle made. The file is SM1E-0G50U0. Every page matches what a dealer tech would have pulled from the shelf in ’91. Aftermarket manuals for this car often omit the FULL ACTIVE suspension data or merge it wrong. I’ve seen one that listed the brake pad wear limit as 1.5 mm — that’s a lawsuit waiting to happen. The Q45 is complex: SUPER HICAS, active suspension, a V8 with a timing chain that requires precise tension. If you’re working on a car like this, you need the OEM documentation. For a broader understanding of OEM documentation standards, refer to the Automotive Industry Overview.

Audience Fit: Who Needs This 1578-Page Manual?

If you’re a home garage enthusiast who’s pulled the engine in an old Q45, you need this manual because one wrong torque and you’re machining the block. If you’re a pro technician who sees a Q45 once every three years, you need it because you don’t have the specs memorized. If you’re a collector keeping a 1991 Q45 on the road, you need it because parts suppliers don’t know your car like Infiniti did. This manual is for anyone who respects factory engineering and doesn’t trust a $15 scanned CD. Related manuals you might also need: Infiniti FX35, FX50 2009 Service Manual – OEM Factory Specs”>Infiniti FX35, FX50 2009 Service Manual – OEM Factory Specs, 2003 Infiniti G35 Coupe Service Manual – Wiper & Washer Systems”>2003 Infiniti G35 Coupe Service Manual – Wiper & Washer Systems, and 2004 Infiniti G35 Coupe Service Manual – SRS & Wiring | 60 Pages”>2004 Infiniti G35 Coupe Service Manual – SRS & Wiring | 60 Pages. When comparing aftermarket manuals, keep in mind the Automotive Industry Overview”>Automotive Industry Overview — OEM data is the only reliable source.

Frequently Asked Questions

Does this manual cover the VNS45DE engine tuning?

Yes. Punk-timing, idle speed, spark plug gap, drive belt deflection, and compression ratios for the VNS45DE engine are all on page 1 and the engine tune-up section.

What is the firing order for the 1991 Q45?

1-8-7-3-6-5-4-2. It’s in the quick reference chart. Write it on the fender before you pull wires.

How many pages are in the 1991 Infiniti Q45 Service Manual?

1,578 pages. That covers everything from the engine mechanical section to the body electrical diagrams. It’s the full factory manual, not a condensed version.

Can I use this manual for rear wheel alignment on a car with FULL ACTIVE suspension?

Yes, the manual explicitly separates specs for “Without full active” and “With full active.” Rear camber with full active is –1°40′ to –0°10′. Without full active it’s –1°25′ to –0°05′. Toe-in is the same for both: 0 ± 1 mm (0 ± 0.04 in). That level of detail is why I recommend this manual over any aftermarket version.

I’ve been doing this for 28 years. I’ve seen guys wreck perfectly good engines because they used a generic manual that said “torque to 45 ft-lb” when the factory spec was 38 ft-lb with a specific tightening sequence. The Infiniti Q45 1991 Service Manual gives you the truth. Access the Factory Manual from AutoRepairManuals and keep it on your bench. You’ll use it every time that car rolls in.