# 89 d21 z24 bad fuel milage



## Ronald (Jan 4, 2008)

I have a 89 d21 with a z24 motor that gets around 8 to 10 mpg.
It had a blown head gasket and I replaced it replaced the plugs with Bosch.
Have replaced the fuel & air filter.

This truck never got over 18 mpg in the first place.

Any ideal what might be the problem??


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## zanegrey (Dec 5, 2005)

read the codes..

alot of times when the head is done the timing is not put back correctly.

check timing and check the oil pump timing..


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## Ronald (Jan 4, 2008)

Timing chain was marked and put back as it was.It got 17 mpg after head was done it just started with the bad milage in the last few weeks.


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## zanegrey (Dec 5, 2005)

check the codes..


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## Ronald (Jan 4, 2008)

zanegrey said:


> check the codes..



Your talking about taking it to auto zone and let them check the codes?????:newbie:


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## zanegrey (Dec 5, 2005)

no.

the ecm is located under the passenger seat..

you can read its code your self..


check out the sticky...


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## smj999smj (Jan 1, 2006)

First thing you should do is get rid of the Bosch spark plugs and put in the correct type NGK spark plugs. Bosch plugs are notoriously problematic on Asian-make vehicles. 

A lot of times when a head gasket blows, it causes coolant to enter the exhaust stream. This can ruin the O2 sensor and ruin the catalytic converter media, as well. If you didn't do so during the head gasket repair, I would recommend replacing the O2 sensor with a genuine Nissan or NTK part. It would also be a good idea to perform an exhaust backpressure test. Checking for stored trouble codes is a good idea as well and could help point you in the right direction. It would also be a good idea to re-check the ignition timing, check the fuel pressure and make sure it's not excessive.


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