Why won't my GMC Jimmy start when it's wet or cold?

Short answer: If your Jimmy cranks fine but won't fire after rain or on damp, cold mornings, moisture is almost always getting into the ignition. Old spark plug wires, the coil wire, or a worn distributor cap and rotor let the spark leak away when they're damp. New wires, cap and rotor are cheap and usually fix it. If it doesn't crank at all, that's a different problem: the starter, battery cables or neutral switch.

Symptom: On a dry day it starts normally. After rain, on humid days, or below about 40°F, it cranks and shakes like it wants to start but won't. Once it dries out or warms up, it starts again.

What to check first

1. Note whether it cranks. Cranking but not starting points to ignition or fuel. No crank at all points to the starter circuit (see below).
2. Do the dark test: at night, open the hood with the engine running and look for little sparks jumping from the plug wires or cap. Lightly misting the wires with water can bring it out.
3. Look at the distributor cap and rotor for cracks, burned contacts or white crust inside.
4. Ask when the cap, rotor, plug wires and plugs were last replaced. If no one knows, replace them as a set.
5. For no-crank: try starting in Neutral, check the battery cable ends for corrosion under the red cover, and have someone check for power at the starter when it won't crank.

Likely causes

1. Old spark plug wires or coil wire. Old wires crack or get porous; moisture gets in and the spark shorts to ground.
2. Worn distributor cap and rotor. The 4.3 V6 uses a distributor. Moisture or carbon tracking inside the cap can kill the spark.
3. Intermittent starter, battery cables or neutral safety switch. These cause no-crank, not crank-no-start.
4. Fuel delivery. Less likely when the problem tracks the weather, but a fuel pressure test rules it out.

What it usually costs

No owner in these threads posted a repair bill. Plug wires, a cap and a rotor are normally an inexpensive DIY parts job; get a written quote if a shop does it.

Is it safe to keep driving?

A no-start isn't a safety issue by itself, but a misfire from bad wires can come and go while driving. If the check engine light flashes, ease off and get it checked soon. Verify with a mechanic.

DIY or shop?

DIY for wires, cap and rotor with basic tools. Replace wires one at a time so you don't mix up the firing order. The starter and cable tests are DIY with a test light or meter.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists no recall for ignition or starting problems on the GMC Jimmy in the model years we could check on 2026-10-24 (the recall lookup returned an error for 3 model-year queries). Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• NHTSA complaints: 431 keyword-matched complaints for GMC Jimmy 1995–2005 (of 1,967 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-24; keywords: stall, dies, shut off, won't start, no start, cuts out, idle, rain, wet, distributor, starter) (NHTSA returned no complaint data for 1 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In '99 GMC Jimmy won't start when cold or wet on Car Talk, a 1999 Jimmy 4x4 wouldn't start below about 40–45°F or when it was humid. Plugs and wires had been changed, but no one knew about the distributor cap and rotor, and members said the secondary ignition (cap, rotor, wires, plugs) was where to start.
• In 1999 gmc jimmy will not start after it rains? on Car Talk, an owner's Jimmy cranked and shook but wouldn't start after rain. The mechanic found no codes, and the fuel filter, pump, plugs and battery checked out. Members said this is a common plug wire problem: old wires get porous, rain gets in and they short out. They suggested looking for sparking at the wires in the dark.
• In 99 GMC 4WD Jimmy Starting Issues on Car Talk, a different symptom: the Jimmy sometimes did nothing at all when the key was turned, then started fine 30 minutes later. Members suggested trying Neutral, checking for corrosion under the positive battery cable cover, and checking for power at the starter solenoid during a no-crank, since starters can fail intermittently. The truck also had an aftermarket remote starter, which can cause intermittent no-starts.

Quick tip

Weather-related no-starts on these trucks are almost always ignition parts. A cap, rotor and set of wires costs less than one diagnostic hour, and they're probably overdue anyway.

Vehicle focus: 1995–2005 GMC Jimmy (and the similar Chevy Blazer) with the 4.3L V6 and distributor ignition.

Safety / mechanic note

A flashing check engine light means a misfire that can damage the catalytic converter. Verify with a mechanic.