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I effing hate fuel injection.


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I'll preface this to say I'm biased, as every EFI Nissan/Datsun I've ever owned has had fuel injection problems that I have never been able to solve, whereas I've always been able to solve carburetor issues by replacing one part.

 

 

So, back in April 2014 I bought a '91 Pathfinder so I could take a trip around the country.  It worked fine, 18,000 miles in a month and all was well.

 

Until I had to pass emissions this year.

 

Didn't get far in the test- cruise HC emissions were through the roof- limit 400, NORMAL is under 180, test was 3650.  You can smell raw gas coming out the tailpipe, it's that bad.

 

Thing is, it seemed to run normal.  Maybe a little rough, but fuel mileage has been the same the whole time I've had it, just under 20.  Got worse the last few weeks but I'd been running the A/C full blast the whole time, and mileage was still around 18.  Not good, but it is a 4WD, heavy Pathfinder.

 

So, causes for high HC are as varied as the weather, but time to check the plugs.

 

#1 is black and sooty.  All the rest are beige.  Well, that's telling.

 

Compression check gives more bad news, but nonsensical news:  going from 1-6, it's 120-120-180-120-90-120.  90 is #5, which had normal looking spark plug and if I pull the plug wire when running the engine RPM drops drastically and gets REALLY rough.  #1, OTOH, has normal compression but pulling the plug doesn't do a thing- sounds exactly the same.

 

Change spark plugs, as they all look really worn and end gap is almost twice the book setting from erosion.

 

Runs worse than before.  Obvious miss.  #1 plug is black and soaked with fuel after 2 minutes.

 

Pro mechanic friend says "stuck injector".  So I get some new ones.  Naturally they're the WRONG ones.  There's "blue" and "black", and they had no "blue" ones in stock, lots of "black", and some marked as "blue or black".  Got those- they were black.  My old injectors are blue.  Go figure.  Check online- says difference is spray pattern, it'll WORK, just not as efficiently.  Would be better to change all 6, but I only bought 3, and in any case replacing the (perfectly fine) even bank ones requires removing the intake plenum.  Odd bank are accessible simply by moving the wiring harness.

 

Changed it anyway.

 

Ran extremely rough on start, smoothed out for 10 seconds, then the miss came back.

 

Checked plugs.  #1 is soaked.

 

Cleaned and swapped #1 and #3 plugs just to be sure it wasn't a bad plug.  Still missing, plug still soaked with fuel.

 

I can hear the injector firing- tick tick tick.  If I unplug the injector when running it makes no difference whatsoever other than the tick from that injector stops.  Same with the spark plug,  Any other cylinder shows a more obvious miss if I pull the plug or the injector lead.

 

Checked #1 plug wire- it's firing the plug fine, but the cylinder is simply flooding.  It appears to be flooding even if I disconnect the injector.  Engine sounds much worse, and has now developed a decelleration backfire.  Raw fuel smell is overpowering, and tailpipe is turning coal black.  But only #1 plug looks bad, the others are just getting a slight tan.

 

At wits end here- I have spark, I have compression, I have an overabundance of fuel even after changing the injector.  If this was batchfire I suppose I could swap a couple injector wires (if I could make them reach) to see if it's an ECU issue?  It just seems like it's dumping fuel into #1 and only #1. 

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before you condemn the ecu check the wiring harness if the wrong wire is shorting to ground the injector would be working over time i would be inspecting the wiring harness with a fine tooth comb at this point in the game to be sure there is nothing shorting 

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If the cylinder is flooding, even with the injector disconnected, then you have to be getting gas from elsewhere. Much more likely it's a spark delivery issue. I would definitely start with Mike's suggestion and trace the wires and verify wiring/firing order. Even if you're 99% sure it's not that, check it and be 100% sure. Is it possible that your wires might be arcing between each other? Are they touching together anywhere?

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I haven't had time to check the FPR.  Don't even know where it is, though the manuals say it's on the back of the engine.  I did knock a vacuum line off when changing #6 plug, and the hose fell apart.  I replaced that,which got rid of the hissing noise but didn't change the obvious miss one bit.

 

I've rechecked the plug wires repeatedly.  The #1 wire is too short to go anywhere but #1.  The dist cap is factory marked (1-2-3-4-5-6) and that's the firing order.  If one was wrong, they'd all be wrong and as I said, 5 plugs are beige-ish and #1 is black.  If I pull it immediately after running, it's wet. but overnight it dries off.   It takes all of 30 seconds  of idle to soak the plug.

 

The plug, though sooty and black after sitting overnight, shows signs of firing as there's a tiny clean spot where the actual arc-ing takes place. 

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So...

#1 plug changed

#1 floods even when injector disconnected? (can't be an electronic problem)

#1 injector has been replaced? (can't be the injector)

 

This leaves fuel pressure? So why #1 and not the rest?

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The AA folks say something like ‘if you and your buddies stood around and tossed all of your problems out on to the table, you would probably pick yours back up again. That concept never rang more true that when reading Dougs post here.

 

I thank that I will hang onto my weird little carb issues, thanks...

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I am, once again, overthinking the problem.

 

Because the "dead" cylinder is #1, I couldn't test it's plug wire on any other cyl as it's too short.  So I tested it by placing a spare spark plug on it and running the engine.  Since I saw spark like the other cyls doing the same test. I figured I had spark.

 

VG30 plug wires are different than any other ones I've had, because they have a solid extension to reach through the plenum and past the upper head casting.  My spares are all L-series, so I didn't swap the wire...  Until tonight, when I snaked a wire in to just check it.  The odd bank wires are accessible enough to use a normal wire, at least temporarily.

 

 

BIG change.  Still missing at first, but you could feel the miss become less consistent as it warmed up.  And the raw fuel smell was gone.  Still had that backfire.  Drove it around for 15 minutes- it's a lot quieter.   I can hear the bad idler pulley growl again.  Backfire went away after a couple miles.  It's still missing, but inconsistently.  It now sounds like crossfire.  #1 plug wire was probably firing down the insulator where I couldn't see the arc, and if that wire was bad I suspect they're all past their prime.  Hell, these could be the original (250,000 mile) plug wires.

 

So it's probably just a set of aged-out plug wires.  Hopefully I can find a set of decent ones locally (not the crap ones the chain stores have).   Then try to pass smog again.

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I used to be the same. I hated EFI. But a few problems with the EFI forced me to either learn it or pay someone to deal with it.

 

I've learned how the circuits and sensors work with each other, like how the TPS works in conjunction with the AFM to adjust the timing. I now understand that EFI is actually much simpler than carburetion.

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 EFI is easy. But then again, I'm 23 years old (never touched a carburetor prior to owning a datsun) and work for Toyota..... I perform software updates and monitor live data for a living.....

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