# 1997 Nissan D21 - Slight backfire during deceleration



## chacono (Oct 30, 2004)

An annoying thing has been happening lately to my 97 Hardbody, 4WD, 5-speed, 190K+ miles. I notice a slight backfire during deceleration - there are no codes, no engine light, nothing...the thing just has a slight, weak, backfire. It's been less than a year since I changed spark plugs, spark plug wires, rotor, cap, air filter, etc. I read about possible causes being "inlet valves sticking or leaking" but I don't smell unburnt fuel or notice smoke from the tail pipe. Any ideas? ...other than this issue, the truck runs fine.

Thanks.

-- Omar


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## smj999smj (Jan 1, 2006)

Do you notice any timing chain rattle?


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## rogoman (Dec 16, 2004)

Having timing that is too late (retarded) can cause backfiring. It can also sometimes happen if your engine is running too rich. When the exhaust valve opens, the mixture isn't done burning so it ignites the unburned fuel in the exhaust system and causes a loud bang.


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## jp2code (Jun 2, 2011)

I'd imagine vacuum leaks could cause this, too.

chacono, have you checked the codes?


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## chacono (Oct 30, 2004)

Thanks for the suggestions - I'll reply to all at once.

- I do not notice the timing chain rattling
- I'll verify the timing and reply asap
- Will check for vacuum leaks - there are no codes


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## chacono (Oct 30, 2004)

Folks. I verified that the timing is within specs, the timing chain is sound, did not notice any vacuum leaks, and still no codes. Since, other than the slight backfire, everything appears well, I will just let my truck be. If I ever find something relevant, I'll post.


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## jp2code (Jun 2, 2011)

I just thought of something. On motorcycles (particularly Harley-Davidsons), owners often install aftermarket intake or exhaust systems. This increases the engine's efficiency, but also results in an extra lean condition unless they have the fueling system tuned to match the modifications. Other motorcycle owners can typically tell when someone has bolted on intake or exhaust parts without getting a tune because of the pops and backfires coming from the engine.

So, do you have an aftermarket air filter or have you changed the exhaust system (glass packs or removed the CAT)?

If not, you could also look for loose exhaust manifold bolts. Usually, you would hear this extra noise. Loose exhaust manifold bolts allow extra exhaust flow, which also results in a leaner running engine - and backfires.


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## ddtwdmb (Feb 17, 2018)

jp2code said:


> I just thought of something. On motorcycles (particularly Harley-Davidsons), owners often install aftermarket intake or exhaust systems. This increases the engine's efficiency, but also results in an extra lean condition unless they have the fueling system tuned to match the modifications. Other motorcycle owners can typically tell when someone has bolted on intake or exhaust parts without getting a tune because of the pops and backfires coming from the engine.
> 
> So, do you have an aftermarket air filter or have you changed the exhaust system (glass packs or removed the CAT)?
> 
> If not, you could also look for loose exhaust manifold bolts. Usually, you would hear this extra noise. Loose exhaust manifold bolts allow extra exhaust flow, which also results in a leaner running engine - and backfires.


That's pretty thoughtful, definitely something to look for. 

Back to the timing chain, what if the rattle was present? Does that mean slack in the timing chain is causing incorrect valve placement during the firing cycle?


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