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Won't Rev past 2000 rpm on the HWY.


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Ok my problem.

The other day my battery died. It was almost dead low on water so I filled the battery up charged it and everything is great, fired right up.

I take the z to work which is all highway. I have a mile to the hwy and it's running fine reving as high as I want it to rev. Get on the hwy cruising at 60-65 reving and running fine for about 3 miles. Then all of a sudden it just dogs down. I have the peddle to the floor and it won't rev higher than around 2000rpm and my speed drops down to like 25-30 mph on the hwy. I take the next exit and after a minute I can get on it again reving it as high as I want to not loosing any power. Coming home it did the same thing. One thing I noticed was the headlight dimmed when this happened.

The guy I bought it from put an electic feul pump in. Is it the pump, battery, carbs, or wiring? I am lost.

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I am guessing its a battery/alternator/VR problem. I would take the batt & alt into your local parts store to have them tested. ( My 2cents is on the alternator)

The dim light, weak spark/ignition, sounds like it's just short on juice.

By having the parts tested, you can avoid just guessing & tossing $$ at the problem.

Good luck, let us know what you find


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Taking the pos off with the engine running is not a good idea, some alternators will burn up with out a load. I don't know if the Z's will or not but it isn't worth the cost to find out.

I would do two things, reinstall a mechanical fuel pump, I take it that you only have the electric, and get the battery tested. In my opinion 2 pumps are better than one, you can still get home if one breaks :)

The battery may have an intermittant short between a couple of cells, this often happens when you run one out of water or if the battery is old (a lot of sediment in the bottom of the battery). This will put a hell of a load on the altenator causing your voltage to drop and may be slowing or shutting off you electric fuel pump.

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Definately sounds electical to me, I put my money on the alternator had a similar problem but when i got mine tested it was putting out ok voltage about 12.5 volts I think. Bought a new battery didn't fix it, but i agree still get it tested and see if anything is obviously wrong.

don't think it would be fuel pump never know.

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Well it looks like it's the relay that runs the electric fuel pump. Took the relay out and jumped it with a paper clip and took it on the HWY. Running great never dogged down at all.

So... The coast was clear:classic: so I brought it up to about 100-105mph for about a one mile strip. Ran great for 3/4 of the mile but it did start sputering toward the end like it wasn't getting enough fuel or air or something.

So I now have a couple questions.

With a properly running relay should the pump be on all the time at the same rate or does it pump more or less fuel depending on the engines need for fuel? I know it turns off/on with the ignition.

What size relay do I get? It had a 16A should I go bigger like 30A or smaller?

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If you are running a stock pump or one from a RX-7 , they run at one speed all the time, that is why you have a return line to the fuel tank. you dident mention are you running carbs or injection. If you are running one of the aftermarket pump like a purilater or AC they rattle faster when out of fuel .

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Sounds to me like your fuel pump isn't getting enough fuel to the carbs for sustained high speed running.

Are you still using the return line to the tank?

If you are, try blocking the return line and taking it on another run, if everything is OK you need a higher output pump. More volume not pressure. I run a Facet electric pump which runs at 4 to 5 PSI and pumps 58 litres per minute.

If your worried about the alternator not putting out enough charge, run the engine at 2400 RPM and check the voltage at the battery, it should be 14 to 14.7 volts.


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The aftermarket pump thats in there right now is a 12V 2.5-4 psi pump.

The flow rate is not marked on the pump so I don't know what that is.

Can someone advise me on what amp relay I should get? The one that was in there was 16A.

I have found a 30A for $26 and a 40A on ebay for like $12.

I am confused on the amp ratings and don't know what to go with.

Thanks you guys are great.

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The amp rating if for the amount of current the contacts can carry. For a relay or solinoid bigger is better. If you use a 40 amp in a 10 amp circuit the contacts should last for ever, where if you used a 5 amp the contacts would burn out.

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