weird engine problem

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Nov 12, 2007 | 11:30 PM

MESTRKR

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weird engine problem

'89 Ranger 4x4, 2.9L V6 new batt. just tuned up.

Once the truck is warmed up, and has been driving for around 10 minutes, it starts acting funny. Without moving the peddle, the engine will operate at the right rpm, then fall off to around 2k, pause, and surge back to the right rpm.

Any thoughts on whats going on.

Last edited by MESTRKR; Nov 13, 2007 at 12:07 AM.

Nov 13, 2007 | 12:50 AM

bigblockford79

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From: W. MI

check for vacuum leaks, especially look for any dry rotted rubber that may have been cracked while doing the tune up. I was once told that you can find vacuum leaks either by listening for a hissing sound or take a can of carb clean and spray it into areas of possibly leaks and if the engine revs up then there is a leak

Nov 13, 2007 | 01:26 AM

MESTRKR

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If that was the case, wouldn't it be a constant problem? Like whenever the engine was running...not just after it was warmed up and driven a few miles?

Last edited by MESTRKR; Nov 13, 2007 at 01:29 AM.

Nov 14, 2007 | 05:26 AM

cddz

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From: Newark, Ohio

2K? the proper idle speed is 672 RPM. Sounds like the IAC. Simple to replace for around $40. You may also want to test your ECT(two wire temp sensor)

Nov 14, 2007 | 05:16 PM

bigblockford79

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From: W. MI

Quote:

Originally Posted by MESTRKR

If that was the case, wouldn't it be a constant problem? Like whenever the engine was running...not just after it was warmed up and driven a few miles?

Quite possibly but also when rubber gets warm it softens and expands and could cause your problem. It was just a cheap and easy place to start and one that many overlook.

Nov 14, 2007 | 09:01 PM

MESTRKR

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I'll take a look at that, thanks for the responses.

The truck idles just fine, it just acts up when you're driving down the road, at say 40-45mph

Nov 15, 2007 | 11:54 AM

BSmitty

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From: Yes

TPS? Check for signal voltage spikes in the pedal movement. You can also use an unlit propane torch to find vacum leaks, open the valve (don't light) and run over the vacum system, or carb cleaner as suggested, both are very effective.

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Nov 16, 2007 | 08:32 AM

pawpaw

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From: SW Va

How about a dirty/sticking PCV valve, it's often ovelooked!!!!

It can be thought of as a calculated for & controlled vacuum leak, when operating as designed, but will upset the air/fuel mixture if acting out & sticking open.

If it acts out after the engine warms enough to go into closed loop operation when the air/fuel mixture leans out & becomes more senitive to unmetered air/vacuum leaks, then it's more likely to be noticed, than when the engine is cold & in the open loop mode, with a richer air/fuel mixture.

Same could be for the Evap & EGR systems, if they are acting out after warm up.

SO, do you have a Check Engine Light & any hard codes set, or any CM/Pending codes stored in the computer, that might offer up some clues???? If so post ALL the trouble code numbers you have, if not, have the computer scanned for set or pending trouble codes & post ALL the code numbers that are found.

Just a couple more thoughts for consideration.

Nov 16, 2007 | 07:21 PM

#10

bazzman1953

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From: Ishpeming Mi.

Quote:

Originally Posted by MESTRKR

I'll check the TPS, haven't been able to get a chance to look at it yet, but the propane torch is a good tip. works well.

Thanks

And I learn yet another thing from this forum. Propane for testing for vacuum leaks. Stupid me, I had used it to see if an MG I had bought back in the mid-eighties for $400 would actually run before I put gas into it. It did so I gassed it up, and it did! The owner was pissed off at it because it overheated. Head gasket, new waterpump, radiator recored, nothing had worked. Yep, it overheaded just idleing. WTF??? All these repairs done and no cure? Hoses had been replaced, along with the thermostat by him. No blown headgasket or anything else I could figure out.
Well dammit...
So I pulled the rad and waterpump to stick a hose in the block and flush the engine out, thinking that a piece of hose had fallen off and was blocking some part of the engine. As soon as I pulled the waterpump off I saw the problem. THERE WAS NO IMPELLER ON IT!!! The idiot mechanic had simply stuck another one on it without looking at it first. Go figure.