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Hey fellas. I just found this forum and wish I had sooner. Found the other nissan forums but not the hb one. Anyway, I have a few questions and rather than dumping a bazzillion posts I figured I'd make a list. So here she goes:

1) Fuel pump. I have recently had the sending unit out twice. Since then I have been hearing a high pitched noise coming from the gas tank. I don't think I could hear it before but maybe it was there. Has anyone had this before? Is my sending unit about to die? It got worse when I forgot to tighten the filler cap and drove across town, then it went away for a few days, then I took it out for 150 k on the highway and when i got back into town it was the worse its ever been. Prior to this my tank had some pinholes and fuel line leaks. Also my return line may have a leak. The high pressure line is all new nylon high pressure hose.

2) Brake booster. My brakes get really spongy off and on, esp if it has dipped below zero. I haven't taken it for a rip on the highway for a long time till the other night and by the end of the trip they were better than they've been since i got the truck six months ago. The aiv reed valve was totally gone and had a remarkable amount of water in it (over a litre i would guess) and so I just took it out completely and capped all the hoses etc. Could it be that my brake booster got water in it and has been freezing or something? If so any ideas on how to dry it out?

3) Rough idle. When I got this truck the thing idled sexily. It was stable as a table and it sounded great mechanically speaking. Over the summer the idle has been getting rougher until you could see the tack wobbling up and down like an old speedometer on a cold day. The gas milage took a shot too (500-550 per tank down to 400). It only started idling rough when I welded the aiv exhaust pipe back into the manifold or wherever it originally was. Anyway. About two weeks ago I got fed up and took the thing out after ppl had said aiv was bs and its gotten better but still getting only 400k to a tank and idling rough, but not near as bad.

4) Lastly it rattles at startup until the oil light goes out and appears to begin to get the rattle when sitting at a stop light but not to the same degree at all, it may be just the low rough idle. I am not sure whether its the timing chain or the lifters making the noise.

I have a feeling all of this except for the fuel pump and the rattling at startup is related to the aiv pumping junk into the vacuum system. Anyway sorry for so much info on the first post but any help would be appreciated. I really enjoy driving this little truck but the squeeks and noises etc worry me for reliability. I want to be able to take it for trips but I don't want to be let down.

Steve, Belleville Ontario - 1990 HB KA24E 2wd
 

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NF Mod/Nissan Master Tech
2006 Pathfinder LE, 2003 Frontier SVE
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The fuel pump whine could be that the pump is going bad or that it is overworking. Test the fuel pressure and make sure the regulator is operating properly. The only relation to the R&R of the sending unit that I could see would be if one of the hoses were crimped and restricting the fuel flow or if one of the connections is leaking. If there is debris in the tank, it could be clogging the sock on the pump. If the return line is leaking, confirm and repair as needed.

An issue with the brake booster would cause a hard pedal, not a spongy one. I can't see any way that a faulty AIV would cause water to enter the booster. Spongy brakes are typically a sign of air in the system or misadjusted brakes. Check the rear brake adjustment, check for signs of brake fluid leakage at the wheel cylinders, calipers, hoses, master cylinder and check for pinholes in the brake lines. If all that is good, bleed the brakes. If the brakes still get spongy, I would suspect a faulty master cylinder.

Rather than remove the AIV (air induction valve), I would have suggested replacing the reed valve inside of it. Would have been a lot simpler and you would have still retained the operation of the AIV. Regardless of what people have told you, it is there for a reason.

The timing chains on these engines are famous for broken plastic timing guides, which were later updated to metal backed guides with new bolts around the 95 model year. Often the reason these guides break is due to debris in the oil channel to the oil-fed, chain tensioner. Low oil pressure could also do this. If the chain guide breaks, the chain could jump a tooth and cause a retarding of the engine timing, which could lead to rough idle. This will also show up when you check the ignition timing and find it off, as the distrbutor runs off the camshaft. I would suggest checking the oil pressure and if that's good, check for a broken chain guide and possible jumped timing.
 
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