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Old 10-05-2017, 06:51 AM   #21
XoXSciFiGuy
 
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Might sound weird...but sometimes when a Nissan will rev up but not give you any power, the pressure plate in the clutch assembly is weak. You can drive it normally, but if you suddenly rev it up, like when you hit it hard to pass someone on the freeway, you don't get any additional power to the wheels. Engine will rev higher but no added thrust. Goes back to normal when you ease off the gas. You can still get higher speeds, but you have to go easy on the pedal.

I don't know...I'm running out of ideas.

One thing I think is almost 'for sure'. You should be getting more than 15mpg, even with that canopy. I think you said you had dual rear axles, though. That's bound to suck some gas, I suppose. The brown/black smoke bothers me, though. I've had a couple of Nissans that were running rich for one reason or another and they never threw a lot of smoke. Not much, anyway...although you could smell the unburned fuel.

Go out to the truck when it's cold...stick your finger up the tailpipe and wipe it around. Is there a lot of black, dry carbon? Or is it wet and black?
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Last edited by XoXSciFiGuy; 10-05-2017 at 07:02 AM.
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Old 10-05-2017, 07:51 AM   #22
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Have you checked your throttle position sensor at all? Sometimes when they go bad it causes dead spots in the acceleration curve. Surging up and down at idle is another common symptom. You can check it with a multimeter. The red wire should be getting 12v with the key on and the white one (signal wire to ECU) should be 0.4-0.6v with the throttle closed and about 5v at WOT. The voltage through the signal wire should change linearly as you apply the throttle. If the base voltage is out of spec you can loosen the two screws that hold the sensor on and rotate it slightly, kind of like setting the ignition timing.
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Old 12-23-2017, 12:03 AM   #23
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Default Mystery not solved, but problem solved!

Well, after almost 2 years of trying everything imaginable, often twice, I decided my only last option was to swap out the TBI to a Weber carb.
The folks at Redline were incredibly helpful, and the carb swap went very smoothly.
Besides having to warm up before driving, she is running as smooth as silk, almost like new. Plenty of power and I am absolutely delighted with the outcome. Haven't had a chance to see how my mpgs are after the swap, but am excited to get her back on the road!
Thanks to everyone for their input and advice. I would have loved to have figured out the problem and solve the mystery, but I am just happy to have her back home and ready for the road!
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Old 12-23-2017, 01:59 AM   #24
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good to hear!

You wont get better MPG with that weber, it will be worse in every way. I only come close to 'normal' mpg when i drive like an absolute grandma and never go up hills.
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Old 12-23-2017, 03:01 AM   #25
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Glad you got.it running! That thing is BA but I do feel bad for that little VG having to lug that sleeper around all the time!
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Old 12-23-2017, 05:56 AM   #26
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Well, about 95% of the sunraders were on a 4 cylinder 100hp Toyota, so having a 3.0 v6 is a rare luxury, which is why I didn't want to give up on her!
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Old 12-25-2017, 11:33 PM   #27
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Very cool rig, for sure. Looks like an all glass shell. Very nice indeed.
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Old 05-07-2018, 02:34 AM   #28
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Default AARRRGGGGHHH...The carb swap didn't solve the mystery issue!

I finally got to take the Sunrader on some long trips that include some long hills. Even though the Weber carb swap definitely gave me more power than the bad TBI, it still never had the same power as before the mystery issue happened. I think I know what is going on (but not why, just what)
It's actually experiencing the same dynamic as before the carb swap. The first 40% of pedal depression gets some acceleration and response. The second 40% still gives nothing in the way of response, rpm increase or thrust. The last 20%, when you floor the pedal seems to kick it down to a lower gear and the rpms shoot up, but the increase in speed doesn't match the massive surge in rpms. It just winds up to probably 6,000 rpm and feels like it is not great for the motor. When climbing a long hill, even a moderate one, that is when I press down on the 40-80% range, and unless it downshifts, I get nothing. Can't even maintain my speed.

I think when we put the carb in, it wound up delivering more fuel to the engine, and that's what made it driveable. But the dynamic of zero increase in power from 40-80% is the exact same symptom and issue as before the carb swap. It isn't a big deal driving around town, because I can just accelerate gently and it's not horrible, just slow. But I can't drive it anywhere where there are hills without feeling like I'm gonna burn up the engine. (Also, grey or black smoke comes out of the tailpipe when I have to stomp on it.)

So whatever was limiting the engine from responding in the 40-80% pedal push down range is still happening. It's just that the carb now gives it more fuel delivery, and it's not as severe.
I also noticed that when I drive for a while trying to gas it in the 40-80% zone, after a bit, it starts to shudder and I can feel it in the steering wheel and gas pedal. (That might also be accounting for the smoke as maybe more gas is going into the motor, but not fully combusting)

It starts up extremely smooth, idles perfectly and quiet. I just still can't get power out of it when I need it.

Any thoughts? I thought I was over the hump, but I am sadly not. It definitely has less power than before the crap went bad. And I thought the carb swap was going to give it more power than ever. (Btw, my mpg went from 14 to under 11)

Thanks for any input. I don't want to give up on her!
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Old 05-07-2018, 03:33 AM   #29
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Forgive me for asking (in case you mentioned it already) but have you checked the compression?
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Old 05-07-2018, 05:04 AM   #30
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Quote:
Originally Posted by cadillacdude1975 View Post
Forgive me for asking (in case you mentioned it already) but have you checked the compression?

Cadillac is right. First place to go is the compression on cylinders.

Now the next time the engine is dead-cold, I want you to take your finger and stuff it up the tailpipe and wipe it around a bit. Are you coming away with black, dry, sooty stuff...or wet, black oily stuff. This is important.

If it's wet and black...it's rings or the like and you're burning oil.

If it's dry and black, the fuel is not burning well, its running too rich, or you have some kind of spark problem maybe. But a compression test on cylinders is definitely needed here. I still wonder about the pressure plate on the clutch. When mine was going bad on my old 1989, you would be on the freeway and step on the gas to pass someone, and the engine revs would go higher...but no power to go faster. When you let off the gas pedal, it went back to normal. And yeah...around town I had to take it easy on the gas pedal or it would slip a little bit. But that doesn't explain the smoking of the exhaust. EDIT: Also take a GOOD look at your exhaust pipe from end of the exhaust manifold to the back. Make sure it isn't dented almost flat somewhere. Restricted exhaust can cause loss of power, too. Doubtful this is the problem, but you might want to eliminate that possibility, just in case.
ANOTHER Edit: When you compression test the cylinders, take a good look at each spark plug. Any fouling, any grey crap on them...maybe one of them way different-looking than the others?

Oh...see my signature below? Below the green truck. Read the last part. Do you have this?

I keep talking about this like it's a manual. Then I saw your reference to gear selector. This is an automatic?
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Last edited by XoXSciFiGuy; 05-07-2018 at 09:42 AM.
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