89 CRX HF fuel milage problems - Fuelly Forums

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Old 11-24-2008, 11:31 PM   #1
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Exclamation 89 CRX HF fuel milage problems

I just put a new remanufactured D15B6 long block in my 1989 crx hf. It is the exact same engine that I took out. The old engine was using a lot oil but was still getting about 42 mpg. The new engine I put in is only getting about 32 mpg. These are supposed to get over 50 mpg. It runs good, just not great mileage. I have new wires, plugs, distributer cap and roter button. I timed it accourding to manufactuers specs. Any of you guys have any suggestions?
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Old 11-25-2008, 05:31 AM   #2
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Does it run great? (good power, good idle, no stumbling)

Did you verify that its the same head as the HF had? The earlier HF's had a higher compression ratio than the regular CRX engines. I'm not sure if the higher CR was a result of the combustion chamber size or the piston top.

Even if the head is the same, I wonder if they installed a DX cam instead of an HF cam. How is the low end torque? Does it have the same amount of acceleration from 1300-1500 rpms?

There is a little more friction produced by new piston rings, this and the cold weather could explain your reduced mpg.
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Old 11-25-2008, 01:14 PM   #3
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It does run smooth, idles smooth, no stumbling but the power is a weak as with the old worn out engine. The head does have 8 valves, I am not sure if that means it is the correct head. Also I don't know if its a DX cam or HF. It seems to have good power taking off but gets weak on the top end. I still have to down shift going up some hills. Someone mentioned a plugged catalytic converter, could that be a possible problem?
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Old 11-25-2008, 01:46 PM   #4
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You can check the cat with a vacuum gauge. Run a hose from the intake manifold into the cabin and watch the gauge as you drive. Accelerate briskly from 40-50 (push the pedal about 1/3 of the way down in 3rd gear)- if the vacuum reading goes down to near zero and stays there (corresponding with you running out of power)- then the cat is plugged because the engine is having so much trouble pushing exhaust out of the cylinders that it can't gulp in much air...
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Old 11-25-2008, 02:54 PM   #5
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To check and see if you have the correct head take the valve cover off and check the rockers. if they are roller rockers then you have a HF head. You can't install a DX cam on a HF because the DX is 16 valve, and is a flat tappet cam.

I think your problem could also be associated with timing. The belt may be back one notch. This would cause a significant amount of power loss like you are describing.

I would also check the Cat like Erik was saying, because if your old engine was using a lot of oil than it most certainly could have plugged the cat up.
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Old 11-26-2008, 01:17 PM   #6
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The cam appears to be an HF cam and I checked the cam timing. I used the marks on the cam sprocket that are in the 3 and 9 o'clock position and aligned them with the joint between the block and head. On the crank pulley I lined the TDC mark up with the pointer on timing belt cover. It appears to be right. There is also a mark at the 7 o'clock position on the cam sprocket and a pointer behind it to line it up with. They are not in line. Is that mark for a different engine? Thanks for all the help you guys are providing.
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Old 11-26-2008, 03:29 PM   #7
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It sounds like the valve timing is correct. I assume that you meant that the two marks on the cam in the 3:00 and 9:00 positions lined up with the valve cover/cylinder head joint (not the cylinder head/block joint).

The cold weather and extra friction from new piston rings could be causing the low mileage- unless there is a vacuum hose loose somewhere or your oxygen sensor is bad.

Did you verify that you have the HF roller rockers?

Are any of your brakes dragging? (Does it roll easily when you are stopped on a slight incline?)
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Old 11-26-2008, 03:59 PM   #8
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It does have the HF roller rockers. I was thinking about taking the catalytic converter off. I looked under the car and it looks like someone before me beat me to it. I have not checked the oxygen sensor, not sure how to. Would it not cause the check engine light to come on if it was bad? It does seem to roll easy enough. One thing I thought of today while reading through a bunch of specs, was that I have 90 weight oil in the trans and the specs called for 10w40? That could be the main issue. I will change that next to see if that helps some.
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Old 11-26-2008, 04:02 PM   #9
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What is the other mark at the 7 o'clock position for?
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Old 11-26-2008, 04:10 PM   #10
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I can't believe that, the book calls for 10w40 engine oil in the transmission? Is that correct. I just assumed it would use a gear oil.
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