Z31 Vacuum Lines under the hood
This page includes lists and diagrams of vacuum lines for the 1986 Turbo (MT). Any differences between models should be minimal, though they may exist—especially as additional control items were added in later years. The diagrams should be very helpful with vacuum diagnostics.
Lengths are approximations, rounded up to the nearest inch, based on the hoses routed in my car at the time of measurement. Except for the vacuum pump lines, all of the lines installed in my Z were stock.
Upon replacement, I modified the lengths on the front gallery lines and A/C lines to minimize cost and hose usage. If you find that stock lengths—or your modified routes—differ from what I’ve listed, please drop me a note so we can compare.
'86 Turbo Engine Vacuum Lines (w/o A/C or Cruise shown) note: 9/86 Turbo cars also have SURGE TANK system and vacuum lines)
Z31 Vacuum Line Replacement
To replace all the applicable engine lines (including all vacuum and coolant lines), you will want to order the following lengths. If you are not replacing certain sections, simply subtract the noted lengths and diameters from the total in the "kit".
Important: These lengths are based on the rerouting modifications I have made on my car. Each measurement is slightly overestimated, and totals are rounded up to the nearest foot. This means you’ll have a little left over from each hose length.
Since hoses are sold by the foot, expect to end up with a few extra inches of material— which is helpful as a backup. If you want to replace the vacuum tank through firewall hose, be sure to add about 6 feet to your order.
Order Needed (Modified Lengths)
| Hose Size | Exact Length | Order Amount | Notes |
|---|---|---|---|
| 3mm | 116" | 10 ft | Base replacement |
| 4mm | 165.5" | 14 ft | Base replacement |
| 6mm | 103.5" | 9 ft | May require 10 ft minimum order |
| 10mm | 56" | 5 ft | Replaces brake booster hose (stock is formed) |
| 3/16" Clear Vinyl | 14" | 2 ft | Available at Home Depot |
Note: Does not include vacuum tank through firewall hose (~6 ft) or vacuum hoses inside the car (A/C controls).
Extra Foot Order (Recommended)
| Hose Size | Recommended Order |
|---|---|
| 3mm | 11 ft |
| 4mm | 15 ft |
| 6mm | 10 ft |
| 10mm | 6 ft (may require 10 ft minimum) |
Z31 Vacuum Line Installation
Installation is straightforward — replace one line at a time to avoid confusion.
Clamps & Fitment
- The stock hose clamps on the 6mm lines will not fit tightly on the new 6mm hoses. You can either modify or replace the clamps.
- While some may run without clamps, it is highly recommended to use them on coolant lines.
-
On the vacuum tank, some connectors have guards around the nipple.
The new 3mm silicone line will not fit because of its wall thickness.
Options:
- Carefully trim the inner width with an Exacto knife
- Or, use a short piece of old hose with a barrel connector to bridge to the new line
Important Warnings
⚠️ Silicone hose can stretch and balloon under pressure. Poorly secured hoses may cause boost leaks.
🚫 Do not use silicone hose in the following applications:
- High heat zones
- Fuel or oil transport
- PCV systems or hoses connected to valve covers
- Other oily emission areas
Driver's Side Front Air Gallery (from front to back)
Source: Thumper300ZX
Source: Thumper300ZX
Source: Thumper300ZX
| Connection | Inner Diameter (mm) | Stock Length (inches) | Modified Length (inches) |
|---|---|---|---|
| (1) to FPR Control Valve (bottom) | 4 mm | 21" | 15" |
| (2) to FPR Control Valve (top) | 4 mm | 23" | 15" |
| (3) to Manifold | 6 mm | 20" | 19" |
| (4) to Throttle (right port) | 4 mm | 13.5" | 12" |
'Driver Side Behind Headlamp'
Passenger Side of Front Air Gallery
'Fuel Pressure Regulator'
'Charcoal Canister Routing'
| Connection | Inner Diameter (mm) | Stock Length (inches) |
|---|---|---|
| (5) to Manifold Front | 4 mm | 3" |
| (6) to FPR | 4 mm | 3" |
| (7) to Carbon Canister (bottom, left port) | 6 mm | 14.5" |
| (8) to Carbon Canister (top, left port) | 4 mm | 16.5" |
Other Vacuum Hoses
'EGR Valve'
'AVI Bottom Lines'
| Connection | Inner Diameter (mm) | Stock Length (inches) |
|---|---|---|
| (9) EGR Control to EGR | 4 mm | 5" |
| (10) EGR Control Valve to Rear Gallery (pass) | 4 mm | 2.5" |
| (11) 'TEE' to Boost Sensor | 3 mm | 7" (5" modified) |
| (12) 'TEE' to AIV Control Valve (Top) | 4 mm | 12" |
| (13) AIV Control Valve (Bottom) to Intake Front | 4 mm | 13" |
| (14) AIV Control Valve (Middle) to AIV | 4 mm | 5" |
| (15) Throttle to Rear Gallery (driver) | 4 mm | 10.5" |
| (16) Manifold to 'TEE' | 4 mm | 35" (25" modified) |
| (17) Intake to Carbon Canister (right port) | 6 mm | 46" (38" modified) |
| (18) Headlight Motor Vent Lines (Clear Vinyl) | 3/16" | 2 × 7" |
| (19) Vacuum Pump to Vacuum Canister | 3 mm | ~26" |
| (20) Carbon Canister (middle port) to Fuel Return Hardline | 6 mm | 9" |
'Vacuum Canister and Charcoal Canister'
Vacuum Tank Hoses
| Connection | Inner Diameter (mm) | Length |
|---|---|---|
| Intake to Vacuum Tank | 3 mm | 46" (modified) |
| Cruise to Vacuum Tank | 4 mm | 28" (modified) |
| A/C Heater Cock Control to Vacuum Tank | 3 mm | 39" (modified) |
| Vacuum Tank to Firewall | N/A | ~6 feet |
Coolant & Brake Booster Hoses
| Connection | Inner Diameter (mm) | Length |
|---|---|---|
| Passenger Side Manifold Coolant Line to Rear Gallery | 10 mm | 9" |
| Passenger Side Collector Coolant Line to Manifold | 10 mm | ~5-6" (OEM formed) |
| Throttle Coolant Line to Driver Side Gallery | 10 mm | 7" |
| Throttle Coolant Line to Turbo Passage | 10 mm | 10" |
| Turbo Coolant Line to Driver Side Gallery | 10 mm | 10" |
| Coolant Reservoir Line to Coolant Tube | 6 mm | 23" (could be shortened) |
| Manifold to Brake Booster Check Valve | 10 mm | 3" (modified // OEM formed) |
| Brake Booster Check Valve to Brake Booster | 10 mm | 4" (modified // OEM formed) |