Backfire followed by power loss

[shawn]

Have a 2000 chevy 3500 van that backfires followed by power loss which only happens when temps exceed 85 degrees outside with high humidity. have had this to several repair shops without any resolution to this problem. almost seems like engine is vapor locks.

Topic

[D]

What have you done exactly to try and eliminate the issue?

Are you getting a check engine light?
What is the condition of the plug wires?

[Daniel Weith]

It would be helpful to know:

Engine
Mileage
Codes if known
Recent service

Has there been any vacuum leak diagnosis?
PCV replaced?
Decrease in fuel economy noticed?
How is the idle?
Do you hear knock/ping during a slow, moderate or hard acceleration?

[EricTheCarGuy]

Yep, start with any codes and check the basics. Here’s a guide on how to go about performance diagnosis you might find useful.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

Please keep us updated on your progress.

[shawn]

plugs wires and distributor cap have all been replaced. No check engine light ever comes on while the problems occur. The engine just backfires
and then loses power. Checked for vacum leaks and never able to find any.

[D]

When it happens again can you pull the distributor cap off and look to see if theres any moisture.

[shawn]

It sounds good idling the problem occurs only after driving the vehicle for about 2 hours straight. Never checked pcv valve. have not found Vacume leakes. The backfire does seem to be coming from the engine rather than the exhaust.

[D]

How long has it been since cap and rotor were changed? Have you replaced the plug wires and are they seated correctly?

Have you checked pickup coil.

[Daniel Weith]

When the spark plugs were replaced did ACDelco plugs get installed?

This is reaching, but maybe there is a bad, defective or damaged spark plug?

[Mike]

Ignition coils can go bad in strange ways. Sometimes, they can fail intermittently beyond a certain temperature threshold, but will seem OK and undamaged when tested when they’re cold.

It’s possible that heat isn’t the culprit, but humidity. If your engine isn’t very clean, especially around the coils and plug wires, higher humidity can make the deposits more conductive, which will increase the likelihood of misfires.

The first thing I would do is to clean things up if needed, and then see if the misfires persist.

[Author]

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