02 Honda Civic P0340

KbarC

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Make
Hoda
Model
Civic
Year
2002
Miles
180k
Engine
1.7
02 Civic 1.7L with about 180k miles. I don't now too much of the cars history. Thing is, car cranks and starts fine, drives fine until it warms up. After about 10miles it gets a sudden and major power loss. About 15mph top speed, rich smell, etc. Even out of gear it feels rough and wont get above 3000-3500rpm. After letting it set awhile it will crank up fine, run perfect for a short while and then do it all over again.

I went and changed cam sensor took it for a test drive and after a few miles had the same problem. Any insight, procedures, ideas would be extremely welcomed!
 

billr

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Fixing this is going to be a lot faster and less expensive if you get the equipment/skills to read live-data. The most inexpensive way is to use an ELM327-type link to a laptop/tablet/phone. Look for "nickb2" here to advise you on that.
 

KbarC

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Some. All i know is at the plug, with key on I have battery voltage (12.2v) one one pin, 5.3v at another and a good ground at the last. I believe this is proper.
 

billr

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Those are readings at the CMP sensor, with the sensor connected to the harness? Just guessing, but that 5.3V on the signal wire doesn't sound right to me. I would expect that sensor to be either 0 or 12.2, depending on the exact position where the engine (cam) has stopped. Try turning the engine slightly by hand, see how that signal changes.
 

KbarC

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Actually, no that was unplugged but i will be out there in just a bit and do that with it plugged in ans see what i get.
 

billr

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Be sure to rotate the crank enough so that the CMP sensor has a chance to change state. That may take as much as two crank turns.
 

KbarC

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I did that and the voltage does go down then back up on the signal wire when i rotate engine. it did the same when cold and running good and when hot and acting up. That seemed to be good.
*** edit*** Just to ad it revs up fine when cold but Running the rpm up while warming up to do hot, once it gets to operating temp the rpms drop down It sets the CEL again and will only rev up to 3500rpm out of gear. it bounces at 3500 like a rev limiter.
 
Last edited:

billr

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This has VTEC, or some other type of complex intake variable?
 

nickb2

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Sounds a bit like we need a bit of live data. But do you know how to do a backpressure test. I have seen this, especially in these honda.

The cats get loose if you will, go good for a while, then o2 send algorithm out of whack.

Since this a 2002 suspect manifold crack at o2 sensor.

so dont overlook that. Once hot would expand. The ecm on these learns hard cold start, learns trims once hot, cat is already cooked.

I took the time to read thread twice to make I didnt miss a word second time through. So Billr is a gentle giant here. When that CEL light appears again, we need that code.

The rest is sniffing in wind like a husky up north;)

You wrote this
It sets the CEL again and will only rev up to 3500rpm out of gear
 

nickb2

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nickb2

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One thing also to not overlook is that this used to be an optispark system. The ECM essentially receives same data on the basic board. Probably wrote that wrong and I dont care.

and yes, it is a vtec, but in my low end experiencing, these hardly ever fail, but that also should not be overlooked.

I will advise further when OP posts a code or two.

In the mean time of this shutdown, a good down country tune to follow.
 

nickb2

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a whole lot of work and a bit of luck;)

If not, WE all shut down. So to my very nice usa neighbors, not the time to start war with very kind neighbors.
 
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