Misfores at cruise

[bingo plebney]

Hi All,

Our '94 Sidekick (1.6L - 16 valve) misfires at cruise. Accelerates fine on all four cylinders, but once cruising speed is reached and throttle is relaxed to maintain speed, one or two cylinders throw in the towel and it runs very sloppily. Seems to be worse once it's warmed up. Recently replaced plugs, wires, air filter, and PVC valve with little change. Vacuum lines appear to be tight too. I suspect an injection sensor. Any ideas?

Thanks in advance,
bp
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For precision work, use a METRIC hammer...

[louthepou]

Hi Bingo,

Sounds like a less than pleasant cruise.

There's a bunch of potential causes, but I'll start by the simple ones and move torwards the dealer-worthy ones. All that being my humble opinion.

1. You mention you changed the plugs / wires, did the distributor cap and rotor get inspected and / or changed? Were the plugs properly gaped? Are you sure the plug wires are snug on both ends?

2. How long has it been since the fuel filter's been changed? I've seen a few vehicles with a 120,000 miles fuel filter preventing it from running.

3. Have the valve clearances been checked / adjusted in the past, say, 20 to 30,000 mi? One or two valves way out of adjustments won't help.

4. How's the compression for each cylinder? A test would at least let you know if the cause could be physical in the combustion chamber.

5. Are the injectors clean? A serious cleaning (not with a bottle in the gas tank, but a mechanic with the equipment) is good somewhere around 60,000 mi, if not more frequent.

6. You've got the same engine as me. Before 96 (I think), the ECM was not yet of the OBD2 generation - which means it's not that informative when comes the time for a diagnostic. It's possible that a faulty sensor is undetected by the ECM. But if the previous checks don't give any positive results, you may have to consider that possibility. This is when a gooood mechanic with both knowledge and experience becomes useful.

The EGR can also play tricks on Sidekicks, but not likely the describred syptoms.

That's all I can think of for now, a sip of single malt might bring more ideas. Feel free to send me q's.

Good luck!

Louis