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Runs bad after starting from hot


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Hey gang.

 

I have a '95 Pathfinder w/ automatic with a ton of miles but is in very good shape. Starting last year I had a problem where I could cold start, run, and go without trouble. But if I start the engine when it's already warmed up it acts like it's running on five cylinders. The rough running lasts just maybe 5-10 seconds and the CEL lights up, but then it smooths out and the CEL light disappears. I don't know which code it's throwing because there isn't enough time to diddle with the ECU before it corrects itself.

 

But twice last week the rough hot running didn't go away. I was out in traffic and wasn't able to get the code from the ECU.

 

With winter coming I'd like to take of this. I brought it to my mechanic but he says my Pathfinder is too old and not worth repairing. Great.

 

Does this sound familiar to anyone?

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Mechanics who can't be arsed to work on older stuff? Yeah, that sounds familiar.


Sounds like a bad fuel injector to me. Probably leaking and flooding one cylinder. I would warm it up, pull the plugs, and see if one is obviously wet or more carbon-fouled than the rest. You can also check the electrical resistance of each injector. The EF&EC section of the service manual should have the acceptable specs and test procedure for that. A fuel pressure test can tell you if fuel is escaping (hook it up, shut if off, see how fast the needle drops), but unfortunately these don't have an easy test point for that.

I would also pull the vac line off the fuel pressure regulator to see if that's leaking fuel into the intake. Long shot, easy test though.


If you go looking for an injector, keep in mind that there are two kinds in these, marked by either a blue dot or a black dot. Ideally you want a matched set. I've got one mismatched injector in mine (repair by a previous owner) and it doesn't seem to care. Avoid the cheap Chinese ones, Cuong had a hell of a time with a set of those recently.

EGR stuck open will make an engine run like crap, but not just on one cylinder, and I wouldn't expect it to show up and go away again on warm starts the way yours is doing. If you reach under the top hat of the valve, you can push up on the diaphragm to open the valve and check that it moves freely. They do tend to accumulate carbon inside.

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Wow, that's all great information. I'll pull the plugs and see if there's any extra fuel in there. A poke with a bore scope won't hurt either. I'll examine the injectors as per the manual - my gut feeling is that it's injector related. If I need new injectors, where can I find the good ones? I'll see if I have the blue or black dot units. Browsing around it looks like Denso and Hitachi both make the correct injectors, so I'll stick with those unless someone knows better.

 

There's no California smog specs on this engine. So whichever EGR system it has is only for Federal specs.

 

Thanks!

Edited by r3dplanet
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  • 2 weeks later...

I had a similar problem a few years ago with around 340,000 to 360,000 miles.
Once I replaced all of the fuel injectors, it fixed all the problems.
The CEL went away (it was intermittent, and usually only when "cold".)
She ran smooth on start up, and highway. 
Fuel efficiently came back to 16mpg to 18mpg. 

You figure that with 25 years, and over 300,000 miles, that yeah, it's about time to replace your fuel injectors. 

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Yup. Agreed. I was finally able to get a code reading of 51 - injector harness. Bought a set of new injectors and seals. I could just find / replace the bad one(s) but clearly with this many miles it's just better to replace all of them.

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My uncle said "Oh, it's too bad you had to replace them all, rather that figure out which ones were the bad ones, and only replace those!"

And I tried to explain to him, that if you have 6 of something, and several are starting to fail, if you only replace the bad ones, you'll have more problems down the road, more performance issues, you'll have to order parts again, and do the work again all over. Your attempt at being frugal in the beginning will cause hassle, wasted time, and wasted expense later down the road. Replace all of them now, and be done with it for another 20 to 25 years. 

I tried to compare it to spark plugs. You replace all the spark plugs, at once, right? Not try to figure out which one was bad, and only that one? 
Right? And he tried to make the case for that too.

Okay, fine. How's about tires. Do you replace all 4 tires at once... or do you only replace one tire at a time, when it's past the legal tread limit?
Weird guy, man. 

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