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Old 06-05-2018, 01:31 AM   #1
bwilson27
 
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Default 88 Z24i bogs on acceleration

It was running unsteady for a few months, then I took out the mass sensor, looked it over and reinstalled it. Big mistake- It made it run really badly at idle, no power when driving.
I have a parts truck, good engine, bad body. So I replaced the TBI, the distributor, the coils and igniters and the 02 sensor. I also traced all the wiring and did find the mass sensor had a badly corroded connector, so took it off donor truck and soldered it onto my harness. Which fixed the erratic idle.
BUT, the truck might idle better, but when parked and revving above around 2000 rpms (no tach) it BOGS and chugs and chokes and wants to die. If I bring it to an idle, it idles fine.
I noticed that when I pull the fuel line off the TBI, there's no pressure, like I would expect in a fuel-injected motor. It has a brand-new fuel filter on it.

I tried putting my old TBI back on, to test, and same thing- Idles good, then as I press the gas, it hits a certain rpm and bogs down with a low-pitched howl. Going back to idle, it's fine, hit the gas, BOGS DOWN.

Pulls code 51, which I believe is for a VG33.

What could it be?
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Old 06-05-2018, 04:53 AM   #2
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Code 51 is an injector code....Check the fuel pressure and see what that shows.
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Old 06-05-2018, 05:06 AM   #3
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I don't have a fuel pressure gauge handy, but I can tell you there seems to be very little pressure at all. After starting, depressing the pedal a few times then turning it off, I pull the fuel line and there's no noticeable pressure. Maybe as much as as a carbed engine might have.
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Old 06-05-2018, 10:48 AM   #4
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Where are you checking the fuel pressure, before or after the fuel filter? Both sides should be strong when the fuel pump is on. If the pressure before the fuel filter is low, the fuel pump is out. If the pressure after the fuel filter is low, the fuel filter needs to be replaced.

Check the resistance of your injectors, too. Do you have a service manual? The injector resistance values will be in the EF & EC section.
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Old 06-05-2018, 03:09 PM   #5
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Checking after the fuel filter.
I do have that pdf manual, but since I took the TBI off a good running motor, I doubted the injectors were faulty. I dunno. I'll try changing the fuel pump today.
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Old 06-05-2018, 04:10 PM   #6
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The injectors also get their power from the Fusible Links, so make sure they are still in good shape. A spark or something could have burned one out.

See http://www.infamousnissan.com/forum/showthread.php?t=35558
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Old 06-06-2018, 02:48 AM   #7
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I understand you are getting injector codes, un bolt the cat and see it that helps. was the problem on mine.
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Old 06-06-2018, 05:10 AM   #8
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I changed the fuel pump today. I didn't help, the truck still hits that BOG when hitting maybe 1500-2000 rpms. I looked at the injectors as it was running and noticed they quickly pulse, rather than a smooth spray. I made sure it was correctly timed-TDC on #1 intake.
The truck idles smoothly, but it's like it has a rev limiter on it or is in limp mode. ECU reads code 55 today. I can drive it, but have to keep the revs low and in a higher gear or it will bog and sputter and buck.

I have a parts '84 Nissan with a Z24 that has the Hitachi carb and vacuum advance distributor. I'm going to swap that stuff onto my engine tomorrow.

I know that the fuel pump pressure is an issue with doing these swaps. Some people add a regulator or find some way to make it work with the FI fuel pump.

I'm tired of chasing problems when I could just make it all much simpler and straight foreward.
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Old 06-06-2018, 11:07 AM   #9
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Make it easier put on a 32/36 weber. More power no bullshit
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Old 06-06-2018, 01:15 PM   #10
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I don't understand why people say carbs make more power. They don't. Its just physics and engine design. They are also far more fuss than EFI. Volumetric efficiency is pretty important and its not very good on a carbed motor but fantastic on direct injection. The closer to direct injection the better.
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