Research note
Power budget, 98 5VZ-FE harness + A/T ECM on 88 4Runner fuses and relays
Scope: which 98 circuits need power, how much current each draws (worked out from the FSM resistances), which 98 fuses protected them, what the 88 side gives you, and the recommended wiring.
Notation: [SRC] = read directly from a manual page. UNVERIFIED = estimate or assumption.
0. Headline findings
- The 98 IG2 B-R feed (II3-8) has no small fuse of its own. EWD p.74 / p.59: ignition switch IG2 (pin 6) → splice I3 → IG1-5 → II3-8 → injectors, coils and igniter +B. The only protection upstream is the 30A AM2 fusible link [SRC EWD p.58–59, 74].
The 7.5A IGN fuse sits on a branch from I3 (J/B 1H-6 → 1J-8, GR-B). It feeds only the EFI relay coil [SRC EWD p.74; RM580U DI-257 ECM Power Source diagram]. So IG2 B-R is not behind IGN 7.5A.
- On the 98, the fuel pump is powered from the EFI relay output. Path: 15A EFI fuse → EFI relay contact (pin 5 → 3) → W-L → splice I5 → circuit opening relay contact (pin 5 → 3, L-O) → pump F10 [SRC EWD p.74].
So the 15A EFI fuse carries ECM BATT + all of W-L + the pump.
- The 88 power topology matches the 98's (the 88 manual we have only shows it for the 22R-E; see §2):
Main 2.0L link → AM2 30A → EFI 15A → EFI main relay (coil fed from IG2 through IGN 7.5A) → ECU +B. ECU BATT also comes off EFI 15A. Injectors are fed straight from IG2 (AM2 30A) [SRC RM077U FI-33, FI-34, FI-39, FI-72, FI-74].
So N5-15 (IG2), N5-12 (+B) and N5-4 (BATT) can be wired one-to-one, as the conversion table already says.
- Nothing is clearly over capacity with the DW100 at 40–44 psi. But the EFI 15A fuse would run at about 11 A typical and about 14 A worst case with the pump on it. That leaves too little margin, so → give the DW100 its own fused relay (§3).
- DLC3 pin 16 on the 98 is constant battery through a 7.5A OBD fuse, not switched [SRC EWD p.58, p.77]. Monch used switched 12V. Both work, but constant power matches the OBD-II standard.
1. Loads on each 98 circuit (math at 12.0 / 14.0 V; worst case 14.5 V with minimum resistance)
1a. IG2 B-R (II3-8): injectors, ignition coils, igniter +B. Protection on the 98: AM2 30A link only
| Load | Spec [SRC] | Current per unit | Steady (avg) | Peak (instantaneous) |
|---|---|---|---|---|
| Injectors ×6 (#10–#60, sequential, high-impedance) | RM580U SF "Inspection: Injector": approx. 13.8 Ω at 20 °C (task brief said 13.4–14.2) | 12/13.8 = 0.87 A; 14/13.8 = 1.01 A; 14.5/13.4 = 1.08 A | Idle: about 2.5 ms per 171 ms cycle (700 rpm) = 1.5 % duty → 6×1.01×0.015 ≈ 0.1 A. WOT, 80 % duty (UNVERIFIED duty) → 6×1.01×0.8 ≈ 4.9 A | All 6 open together ≈ 6×1.08 = 6.5 A |
| Ignition coils ×3 (I3/I4/I5, + side B-R) | Primary 0.67–1.05 Ω cold / 0.85–1.23 Ω hot (RM580U IG on-vehicle inspection) | Ohm's law gives 14/0.67 = 21 A, but the igniter current-limits. Limit about 6–7 A (UNVERIFIED, typical Denso DLI) | Each coil fires once per rev. 3 ms dwell (UNVERIFIED), triangular ramp to 7 A → avg ≈ 0.5×7×duty. At 6000 rpm: duty = 3 ms × 100/s = 30 % → 1.05 A per coil → ≈3.2 A. At idle: duty 3.5 % → ≈0.4 A | About 7 A, plus some overlap with the next coil at high rpm → ≈10 A (UNVERIFIED) |
| Igniter I2 +B (pin 9) | no spec | logic only, ≈0.1–0.2 A (UNVERIFIED) | 0.2 A | 0.2 A |
| IG2 total | Idle ≈ 0.7 A; WOT 6000 rpm ≈ 8.3 A | ≈ 13–17 A for milliseconds (injector + coil overlap) |
- Key ON, engine off: the injectors and the igniter don't drive without the ECM, so the load is ≈0.2 A.
- Bluetop 310cc injectors: the math above assumes they're high-impedance like stock (about 12–14 Ω). Their resistance was never measured (TODO). If they read 2–3 Ω (low-impedance), the 98 ECM's drivers won't survive (the 98 has no solenoid resistor). Each one would pull about 5 A. Measure them before first key-on. This is the single biggest unknown in the IG2 budget.
1b. EFI relay output W-L (II3-16 + E12-23 +B). On the 98 this comes off the 15A EFI fuse
Everything on the W-L bus (EWD p.74–76, splices I5/I10/I11): ECM +B, MAF +B, IAC common (pin 2), VSV EVAP, VSV vapor pressure sensor, DLC1 +B, H3 O2 heater B1S1 +B, H4 O2 heater B1S2 +B, COR coil (pin 1) and COR contact (pin 5) → fuel pump.
| Load | Spec [SRC] | Current |
|---|---|---|
| ECM +B (E12-23) | none in the RM | 0.5–1.0 A (UNVERIFIED) |
| MAF +B (M1 pin 1, hot-wire) | none | 0.5–1.0 A (UNVERIFIED) |
| IAC rotary solenoid, 2 coils (RSO/RSC) | 17.0–24.5 Ω cold, 21.5–28.5 Ω hot (RM580U IAC on-vehicle insp.) | One coil: 14/17 = 0.82 A. The ECM drives them in complementary duty, so the sum is ≈0.8 A. Both on: 1.65 A |
| VSV EVAP (V7) | 30–34 Ω (RM580U) | 14/30 = 0.47 A |
| VSV vapor pressure sensor (V8) | 37–44 Ω (RM580U) | 14/37 = 0.38 A |
| O2 heater B1S1 + B1S2 (H3, H4) | 11–16 Ω at 20 °C (RM580U). ECM flags P0135/P0141 above 2.35 A per heater (DI-189) | 14/11 = 1.27 A each → 2.55 A. Fault limit 2×2.35 = 4.7 A |
| DLC1 +B | reference only | ≈0 |
| 98 COR coil | no spec | ≈0.15 A (UNVERIFIED) |
| W-L subtotal, no pump | typical ≈ 5.5–6.5 A; worst ≈ 9.5 A (ECM 1 + MAF 1 + IAC 1.65 + VSVs 0.85 + heaters 4.7 + COR 0.15) | |
| Fuel pump through COR contact: DW100 | 4.2 A @ 40 psi / 13.5 V (DW datasheet). 98 regulated pressure is 38–44 psi key ON (RM580U SF-6/7) | ≈4.2–4.6 A running. Start-up inrush maybe 2–3× for under 100 ms (UNVERIFIED). 6.6 A only at 100 psi (dead-headed, or the regulator fails) |
| W-L + pump | typical ≈ 10–11 A; worst ≈ 14 A, or 16 A if the regulator fails |
1c. BATT (E12-14 L-R): ECM memory
- From the 15A EFI fuse, direct, never switched [SRC EWD p.74; RM077U FI-34 shows the same for the 88].
- Draw is only mA (keep-alive). It doesn't affect the budget.
1d. FC → COR → pump
- FC (E10-18, G-Y, II3-26) is an ECM transistor that grounds the COR coil. The current is only the coil current.
- 88 COR coil L1 (+B–Fc): 88–132 Ω [SRC RM077U FI-73 (22R-E COR)] → 14/88 = 0.16 A. The 98 ECM was built to drive a COR coil, so this is within its normal duty (98 coil resistance not specified; assumed similar, UNVERIFIED).
- 88 COR has a second coil, L2 (STA–E1, 17–25 Ω), energised from ignition ST1 while cranking [SRC FI-73]. The 88 COR runs the pump during cranking even before the ECM sees NE. That's harmless, and it's a useful redundancy.
- Pump current path: see 1b.
2. 1988 side: what the manuals actually say
Important limitation: toyota_truck_and_4runner_88.pdf (RM077U) covers RN-series (22R/22R-E/22R-TE) only. Foreword (PDF p.1): "Applicable models: RN50, 55, 61, 66, 70, 75". Its FI section is titled "EFI SYSTEM (22R-E, 22R-TE)" (PDF p.207).
There is no 3VZ-E (VZN) content in it. The 3VZ-E repair content would be in a separate supplement, and the fuse box layout and what each fuse feeds would be in EWD040U. Neither is on hand. Everything below is 22R-E or chassis-common, and is marked as such.
| Item | 88 value | Source | Applies to the 3VZ-E truck? |
|---|---|---|---|
| Main fusible link | 2.0L (2.0 mm² link) | FI-33/34/72 (PDF p.238, 239, 277) | Probably (chassis). UNVERIFIED for VZN |
| AM1 fusible link | 40A | CH-3 (PDF p.366), photo labels | Probably (chassis) |
| AM2 fusible link | 30A | CH-3; FI-33 | Probably (chassis) |
| EFI fuse | 15A, battery-fed after AM2. Feeds the EFI main relay contact (→ ECU +B) and ECU BATT | FI-33, FI-34, FI-72 | 22R-E confirmed. 3VZ-E UNVERIFIED (Monch's sheet also says "15A EFI") |
| IGN fuse | 7.5A, IG2-fed. Feeds the EFI main relay coil | FI-33, FI-72 | Same caveat |
| EFI main relay | 4-pin. Coil 1–2 = 60–80 Ω (→ 0.2 A). Contact 3–4 open. Contact rating not given | FI-72 (PDF p.277) | Contact rating UNVERIFIED (typical Denso 4-pin relay about 20 A, UNVERIFIED) |
| Circuit opening relay | Dual coil: STA–E1 17–25 Ω, +B–Fc 88–132 Ω, contact +B → Fp. Its +B comes from the main relay output | FI-73 (PDF p.278) | 22R-E version. 3VZ-E COR assumed the same (it's what Monch grounded at N5-8) |
| Injector feed | IG2 direct, AM2 30A only, through the solenoid resistor (2–3 Ω each). 22R-E injectors are low-impedance | FI-39, FI-74 (PDF p.244, 279) | Shows the 88 IG2 circuit was built to carry injector current. 3VZ-E injector type UNVERIFIED |
| ENGINE fuse | 15A (charging-system check, IG side) | CH-3 | Don't use it for the swap. Unknown what else it feeds |
| CHARGE fuse | 7.5A | CH-3 | Don't use |
| Starter relay (M/T) | Clutch-start relay near the solenoid resistor. Coil ST–E, contact +B–Mg. No rating given | ST-12 (PDF p.363) | Starter circuit fuse/link not stated |
| What else shares 88 EFI 15A / IGN 7.5A | Not in RM077U | — | Needs EWD040U |
98 fuses for comparison [SRC EWD p.58–59, 74–77]: EFI 15A (battery, after 100A ALT → main), IGN 7.5A (IG2 → EFI relay coil), STA 7.5A (ST2 → ECM NSW, A/T), STOP 10A, GAUGE 10A (MIL), OBD 7.5A (battery → DLC3 pin 16), AM2 30A, AM1 40A, ALT 100A.
(RM580U's fuel pump on-vehicle page lists "ALT 80A". EWD says 100A ALT. This doesn't matter for the swap.)
ECU-IG 10A (IG1) does not feed the engine ECM. The 98 ECM's only power inputs are +B (E12-23) and BATT (E12-14) [EWD p.75; RM580U Terminals of ECM].
3. Recommendations
| 98 circuit | Feed it from (88) | Load | Fuse / relay | Wire |
|---|---|---|---|---|
| IG2 B-R, II3-8 | N5-15 B-R (88 IG2, AM2 30A) | idle ≈0.7 A; WOT ≈8.3 A avg; ms peaks ≈13–17 A | Toyota used no fuse here (AM2 30A only), so one-to-one matches stock. Optional, my judgment: an inline 20A fuse near the splice, because the 98 harness wire is thinner than the 30A link (15A would work but has less margin for coil/injector overlap peaks) | 14 AWG (2.0 mm²) for any new length |
| +B W-L, II3-16 and E12-23 | N5-12 B-Y (88 EFI main relay output, 15A EFI) | ≈6 A typical / ≈9.5 A worst with the pump moved off | Keep the 88 EFI 15A + 88 EFI main relay. Bond II3-16 and E12-23 together as on the 98 | 16 AWG minimum; 14 AWG preferred |
| BATT, E12-14 | N5-4 G-Y (88 EFI 15A, constant) | mA | Existing 88 EFI 15A | 18–20 AWG fine |
| FC, II3-26 | N5-8 G (88 COR Fc coil ground) | 0.16 A | none | 20 AWG |
| DW100 pump | New dedicated relay (30 A Bosch-type): pin 30 ← new 15A fuse from battery / AM-side bus (UNVERIFIED tap point, needs EWD040U; a fused lead off the battery + is simplest). Pin 87 → pump +. Pin 86 ← 88 COR Fp output (the old pump feed). Pin 85 → ground | 4.2–4.6 A run, 6.6 A dead-head, inrush brief | 15A fuse (DW: 6.6 A max → 10A would also hold, but 15A gives inrush margin and suits 14 AWG) | 14 AWG pump power and ground, per DW. Relay trigger 18–20 AWG |
| DLC3 pin 16 | New 7.5A fused constant battery feed (as on the 98, OBD fuse). Switched also works (Monch) | under 1 A | 7.5A | 20 AWG |
| STA, II1-6 / starter 50 | N5-9 B (88 starter relay output) | ECM STA is a sense input, mA. Starter solenoid pull-in is the 88's existing circuit | no change | new solenoid lead: 12–14 AWG (UNVERIFIED solenoid draw) |
Why the separate pump relay:
- (a) 88 EFI 15A would otherwise run at about 11 A typical / about 14 A worst, roughly 75–95 % of rating.
- (b) The 88 EFI main relay contact rating is unknown.
- (c) Voltage drop: the pump's flow at 40 psi depends on voltage, and the 88 pump feed runs through the main relay, the COR and the body harness (gauge UNVERIFIED, probably about 16 AWG/1.25 mm²).
- Using the COR output as the trigger keeps all the safety logic (crank STA coil + ECM FC/NE shut-off), and it pulls only about 0.15 A through the old path.
- If you keep the pump on the stock path instead: it is within the 15A fuse at normal pressure (Toyota ran the 98 pump the same way), but check the voltage at the pump under load (TODO item) and expect a blown EFI fuse if the regulator ever dead-heads (≈16 A).
Over-capacity flags
- Not over: IG2 on AM2 30A (≈8 A avg). 88 EFI 15A with the pump moved off (≈6–9.5 A).
- Marginal: 88 EFI 15A if the DW100 stays on it (≈11–14 A; 16 A dead-headed).
- Unknown: 88 EFI main relay contact rating. What else, if anything, shares 88 EFI 15A / IGN 7.5A on the 3VZ-E truck. Both need EWD040U.
- Potential failure: bluetop injectors, if they turn out low-impedance (≈5 A each into ECM drivers rated for ≈1 A). Measure them.
Pre-power checks (add to the TODO / multimeter list)
- Measure the bluetops: they must read about 12–14 Ω.
- With the key ON and the engine off, clamp-meter N5-12: expect about 3–5 A (heaters + IAC + VSVs + ECM + MAF).
- Running at 40 psi, measure pump volts at the pump connector. If it's below 12.5 V with the engine running, it's under-fed.
- Confirm the 88 fuse box ratings and loads against EWD040U when it arrives.
Sources used
- EWD319U Engine Control (5VZ-FE) p.74–77; Power Source p.58–59 (rendered).
- RM580U: Injector inspection; Ignition System on-vehicle inspection; IAC on-vehicle inspection; VSV EVAP; VSV vapor pressure sensor; Heated O2 sensor; DTC P0135/P0141 (DI-189); ECM Power Source Circuit (DI-257); Fuel Pump Control Circuit (DI-261); Terminals of ECM; SF-6/7 fuel pressure.
- RM077U (
toyota_truck_and_4runner_88.pdf, 22R series only): Foreword p.0; FI-33 (p.238), FI-34 (p.239), FI-39 (p.244), FI-72 (p.277), FI-73 (p.278), FI-74 (p.279); CH-3 (p.366); ST-12 (p.363). - DW100 datasheet values, from TODO.md.