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Discussion Starter #1
89 hb had a rough idle like plug wires were bad and cross firing. Hunted for bad wires and since all were old I replaced with a wire kit, plugs and distributor. Cap and rotor were new and looked good, no pitting or burn marks on the interior. A visual check of the fuel flow thru the injector looked reasonable. Checked the codes, mode III showed 55, did a mode IV and those items checked good. Looked for loose hoses and found the brake booster hose had a crack near the clamp so I cut it and reattached. When it idles it runs rough but will accelerate smoothly. I held my hand over the air intake and it seems to smooth out a little when I restrict the air flow. I am thinking an air leak somewhere and my restricting the flow into the air intake is compensating for the leak. It also has great acceleration on the road when I open the throttle but returns to a stumble and slightly rough run when a steady state of cruise is reached and the greater air supply is no longer needed. Now I am thinking maybe i need to do a mode V and check the air flow meter in real time. Are these symptoms of a dirty mass air flow wire or something else? It's in the driveway with the keys if someone wants to take a stab at it! Thanks
 

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Get a can of carb cleaner,and spray it around the intake mounts,vacuum tees,and any other flanges.If the idledrops a little,there's your leak.
Good Luck
 

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fuel filter ..

check for crap in gas tank.

try re routing the fuel pressure regulators vacumn to a manifold source...

what is your idle set at ? is it tooo low ..

what is your base timing set at ? is it too low ..

remember the oil pump timing ..is ur dizzy in the middle or is it cranked to one side or the other of its adjustment range ??



also check your bat post and fusible links for looseness and or corrosion...
check all electrcal conections for looseness or bad grounds..
 

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Discussion Starter #4
throttle body gasket

fuel filter ..

check for crap in gas tank.

try re routing the fuel pressure regulators vacumn to a manifold source...

what is your idle set at ? is it tooo low ..

what is your base timing set at ? is it too low ..

remember the oil pump timing ..is ur dizzy in the middle or is it cranked to one side or the other of its adjustment range ??



also check your bat post and fusible links for looseness and or corrosion...
check all electrcal conections for looseness or bad grounds..
Did a bunch of trouble shooting on this one and got very close. And thanks for all the suggestions. I noticed it ran great under hard acceleration but poorly at steady state, idle and cruise. And it ran a little better when I closed off the air supply over the throttle body with my hands. I surmised an air leak somewhere because it ran better when more air was needed as when accelerating but poorly when the air supply was more than needed. Turns out the throttle body gasket was in pieces and letting air in that was not needed. The dealer, Crown Nissan of Greensboro, is telling me that the gasket is not available unless the the throttle body heater plate is replaced, the gasket is not sold seperately. That means buying a $190 heater plate to get the $36 gasket. I removed the throttle body and it does not look like the gasket would be too hard to duplicate, especially at a savings of $190. Any body been down this road and got any suggestions?
 

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Discussion Starter #6
Thanks for the info. Found the part,# crb 27782 on the NAPA website. Ordered it sent to the house for about $15.00. Looks like the right part after comparing the base of the throttle body to the website picture. Will post the results.
 

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Discussion Starter #8
new gasket,no relief

put the new throttle body gaskets in today and there is no change in the rough running. Spent about thirty minutes with the engine idling trying to find an air leak. Sprayed, listened, pulled hoses and no change. Seems even more aggravating now that I have spent so much time trying to find and fix the problem. Gonna check the timing and fuel filter, both basic and cheap. Working thru all your suggestions, thanks.
 

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Discussion Starter #9 (Edited)
No Air Leak. Bigger Mystery!

Finally found the problem but I am even more perplexed than before all this started. The previous posts tell the story. Finally got the truck to Foreign Accents in Greensboro. They are my resource when I can't figure stuff out. They have the talent, been doing it for about thirty years. I noticed driving the truck to them yesterday that the problem was getting much worse, running rough now at all throttle postions. I had gone from thinking an air leak problem to an ignition problem to a fuel delivery problem. Now after checking all the usual suspects and tips from the board I was still stumped. They came to the lobby with the eight spark plugs, five of which are completely closed with the electrode bent to the tip, not flatened like a piston had hit it but bent over like you had just pressed on the electrode at the end and pushed it into the tip of the plug. All five were black from carbon. I don't know what postion the good or bad plugs came from since I did not take them out. The last person to work on the plugs would have been the tech at Crown Nissan. These did not get bent during installation, I have been installing plugs for almost fifty years and five plugs don't end up looking like that from normal installation unless you drop it to the floor. There were no marks on the plugs, compression was good. I even pulled the new plugs out when I got home to see if they were getting hit by a piston but of course they were not. I am totally stumped. This will bug me for several reasons. First, I thought it was a spark issue but I did not check the plugs, and secondly, how the heck did the gaps get closed without the piston doing it and leaving no marks on the plugs, and thirdly, why did it get progressively worse running over a period of time instead of immediately if indeed the plugs were bent by me on installation or the tech at the dealer?
:wtf:This is gonna take several beers to figure out.
 

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Call Ghost Hunters, and have them set up cameras and EVP recorders in your garage.J/K It's good to hear you got you truck running. Two reasons I can think of:
1 - If the dealer did it, I could see it getting worse as unused fuel residue would build up on the plug, If the gap was not entirely grounding out the plug, but extremely small gap, and the spark was too weak to fire all the fuel.
2 - The garage that you took it to, had a chance to bust the dealers balls, as they like to do to get business from them, after finding gas fouled plugs were the problem. It's hard to imaging an engine running with 5 collapsed spark plugs, unless 4 were on the exhaust side. Even then, it would have a bad miss, and loss of power.
Good Luck
 

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Discussion Starter #11
The theory about carbon accumulation seems plausible. The garage that found the problem did not know of the prior dealer visit and they are not the type of people that need to degrade another's work. Their work speaks for itself after thirty years of excellence.
 

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That's great, that you have a mechanic you can trust. I used to have a foreign car repair shop owner, when I lived in WV, that if he didn't have time to get one of our trucks in, he would tell me what was wrong with it, and our mechanic or me would fix it. We would pay him for the info, as he was 99% right on the money. I learned a lot from him about these trucks. Out here in Columbus, almost 6 years now, I have yet to find one that doesn't try to stick their hand in your pocket-and that included one neighbor
I'ld be working on something, and he would come over and say he could fix it for "this amount". He asked for help one day on something, and I told him I would help for "this amount", and he hasn't come over since, when I was working on something.
Don't get me wrong, I don't expect help for nothing, but don't tell me my gas shocks are leaking oil, either.
 

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clean your air flow meter! Also check your egr system for leaks especially if the rough idle starts once it warms up!
 

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Also check to make sure your muffler bearings arent worn out.


lol hehe, j/k
 
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