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Mike V.
Mike V., Nissan Technician
Category: Nissan
Satisfied Customers: 23620
Experience:  Nissan factory trained and Certified Subaru Technician.
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97 Nissan Pickup: 4X4..accelerate..throttle..The fuel pressure, volume

Customer Question

I'm working on a 97 Nissan Pickup 4X4 5speed manual 4cylinder. The problem is the truck will accelerate under part throttle ( about 40% or less as shown on my scan tool ) , but over that it falls on it's face until it loses about a thousand rpm then picks up again. The fuel pressure, volume and quality are all good. There are no computer codes stored. I have replaced the fuel filter, distributor cap , rotor , plugs and wires. I have also replaced the mass air flow sensor and the front O2 sensor. The throttle position sensor checks good with my scanner and DVOM. The swirl control valve seems to function properly. I unplugged the vacuum line from it anyway to rule it out, and that made no difference. What am I missing? I have a diesel repair shop and don't normally work on imports, but this is a good customer. I don't want to throw anymore parts at it. I changed the mass air sensor at the advice of one Nissan expert on here. I didn't think it was bad because it checked ok on my scanner and DVOM, and it wasn't.
Submitted: 7 years ago.
Category: Nissan
Expert:  Mike V. replied 7 years ago.
Hi there! Do you have to be going down the road for this to happen or will it do it right in the shop?
Customer: replied 7 years ago.
It will do it in the shop in neutral too. Thanks for the fast response. I'm in and out of the office helping customers, but will try to stay close.
Expert:  Mike V. replied 7 years ago.
I believe the distributor is probably bad. Very common problem on these. To verify, take a timing light and watch the mechanical timing when you rev the engine. You might even see it at idle, but what you are looking for is the timing bouncing all over the place. These have a high distributor failure rate, but no real good testing when they become sparadic like this. This is a pretty good way to tell though. let me know and take all the time you need
Customer: replied 7 years ago.
I suspected the distributor early on, but could not prove it so I moved on. I checked the timing and at idle it's steady, but reved up it gets erratic. I ordered a distributor and will install tomorrow. I will follow up after that. Thanks, Len
Expert:  Mike V. replied 7 years ago.
Sounds like a good plan to me!
Customer: replied 7 years ago.

Well I tried the new distributor and it didn't fix the problem. I checked the timing with the new one and it's steady, so I put the old one back in and the timing is steady with it now. My light may have mislead me yesterday. It is an adjustable one, and sometimes has a mind of it's own. There is an exhaust leak between the manifold and pipe and the rear O2 sensor may be bad, it reads .000 not running and 1.25 running. I'm going to address these two isues just to rule them out. I suspect the O2 may be reading right though because it runs real rich.

Expert:  Mike V. replied 7 years ago.
Well, I am not happy to hear that it didn't work for sure!
I really thought that was the problem based on the description.
Test the other stuff and let me know. Not to sure about the rear O2,should only produce up to 1.0 volt by itself. However it could be feeding the ecm the wrong info causing a bad mixture.
Customer: replied 7 years ago.
Well I got it fixed finally. I fixed the exhaust leaks and replaced the rear O2. But, I think the main problem was the timing chain. I was in the process of performing a cylinder leak down test just to rule out a valve problem , when the cam jumped time. I was trying to back the engine up a little to test a cylinder and the chain jumped the crank gear. Then I noticed the wear pad was missing from the guide plate. I can't prove the cam was out of time before this happened, but my guess is it was. So I replaced the timing components, the rear O2 and fixed the exhaust leak, and the truck runs perfect. I don't know which one fixed it, but my bet is the timing chain. I would like your opinion if you don't mind. Thanks for your help, Len
Expert:  Mike V. replied 7 years ago.
I totally agree. If the slack guide pad was missing that chain can jump all over. Probably when you tested the timing with the timing light the chain was jumping and I mistook it for the distributor failure which is much more common of the 2. I appologize for giving you bad info.
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Customer: replied 7 years ago.
No need to appologize, I don't think you gave bad info. I think my timing light was the culprit there, since the distributor is driven by the oil pump that is driven off a gear on the crank. That would seperate the valve timing and the ignition timing making it impossible to see with a timing light. Thanks for the help, Len
Expert:  Mike V. replied 7 years ago.
Thanks for the accept Len, I appreciate it! I am glad to hear it is all good now as well.