Runs rough at low rpm and high rpm - Ranger-Forums - The Ultimate Ford Ranger Resource


2.9L & 3.0L V6 Tech General discussion of 2.9L and 3.0L V6 Ford Ranger engines.

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Old 07-17-2016
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Runs rough at low rpm and high rpm

I have a 2000 Ranger with a 3.0 and it has started running rough at just above idle and at high idle. I thought it was a misfire due to bad plugs, but after changing out the plugs, it hasn't changed. I noticed that #4 and #6 plugs were saturated with fuel so I checked spark on all cylinders. I'm getting good spark so I'm not sure what to check next. I'm thinking compression, since it's not throwing any codes, but any advice would be greatly appreciated.
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Old 07-17-2016
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Welcome to the forum.

Just to be clear.
When you turn on the Key the CEL(check engine light) comes on, and then goes off after engine starts, so you know CEL is working.
And you checked for codes in memory and none were found

You didn't mention cold and warm so.......
Engine runs fine at all RPMs when cold
After it warms up it idles fine, under 850 RPMs
Above 1,000RPMs it starts to run rough, and then smooths out above 2,000RPMs

I have read that 2000-2001 3.0l Coil packs had problems, but that should cause a code on spark feedback and misfire.

Compression issue should set misfire code

Fuel pressure wouldn't, 2000 Ranger should have fuel pressure between 60-70psi when running and drop to no more than 45-50psi when shut off, and hold that pressure for weeks.
There is a pressure fitting on the fuel rail, looks like a tires air valve because that is what it is, a schrader valve, and works the same way.

Testing fuel pressure can tell you of lower pressure than needed but also if a fuel injector may be sticking open, causing rich condition.
You mentioned spark plug tips with fuel on them..................
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Old 07-17-2016
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Thanks for the reply Ron. The issue is at cold start up and is consistent even at operating temperature. I'll check fuel pressure and see what I get and at least eliminate that possibility.
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Old 07-17-2016
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Good info.

Computer doesn't use most sensors on cold start, so doubt it is a sensor issue, and if it doesn't get better or worse when warmed up that just confirms it isn't a sensor issue.

Computer monitors spark and no code, computer can only "assume" fuel pressure, no way to monitor it so that would be best place to start.

Now it could be a vacuum leak, but easy to test for that after engine is warmed up.
Engine warmed up and idling
Unplug the wires on the IAC(idle air control) Valve, upper intake front
Idle should drop to 500rpm or engine may stall, either is good, it means no vacuum leaks
If idle stays at 700 or higher then there is a leak.
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