Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Jeep WagoneerFACTORY OEM SERVICE PROCEDURE
Functional Test
- Inspect Manifold Absolute Pressure (MAP) sensor vacuum hose connections at throttle body and sensor. Repair as necessary. Test MAP sensor output voltage at MAP sensor connector terminal "B" (as marked on sensor body) with ignition on and engine off. Output voltage should be 4-5 volts. Voltage should drop to 1.5-2.1 volts with a hot, neutral idle condition.
- Test ECU terminal No. 33 for the same voltage as above to verify wire harness condition. Repair as necessary. Test MAP sensor supply voltage at sensor connector terminal "C" with ignition on. The voltage should be 4.5-5.5 volts. Same voltage should also be at terminal No. 16 of ECU wire harness connector. Repair or replace wire harness as necessary.
- Test MAP sensor ground circuit at sensor connector terminal "A" and ECU connector terminal No. 17. See Figure or Figure . Repair wire harness as necessary. Test MAP sensor ground circuit at ECU connector between terminal No. 17 and terminal No. 2 with ohmmeter.
- If ohmmeter indicates an open circuit, inspect for defective sensor ground connection on flywheel/drive plate housing near starter motor. If ground connection is good, replace ECU. If terminal No. 17 has a short circuit to 12 volts, correct condition before replacing ECU.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
Comes to youSame-day available12-month warranty
Get a Free QuoteNo obligation. See pricing before you book.