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New Fuel Pump & Now It's Really Rich

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Fitted new fuel pump 280zx efi OEM replacement same as what Z car depot sells (Acdelco) But now the car idles and runs really rich, visible smoke etc. I am thinking the previous owner may have played around with the AFM trying to compensate for a dying fuel pump. Tomorrow i will be checking the fuel damper to see if thats been "adjusted". Does anybody know if there are any Benchmark settings for AFM's, Actually this car is driving

me to drink, which is ok, 'cause I don't mind a bourbon or two!.......thanks in advance.

Edited by cruza

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Sorry for the edit, i forgot to put in its EFI.......apologies to jalexquijano

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Have you measured impedance of your fuel injectors? I would definitely check fuel pressure regulator, but the tune may have been adjusted to compensate for not enough fuel before. The new pump may now be delivering too much fuel.

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make sure the cold engine sensor (it has a fuel injector type connection),  and signal to the ecu are working correctly, might be over fueling.

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I am going to check cold engine sensor this morning and have ordered a malpassi regulator, thanks for the feedback, I know bugger all about EFI, but pretty handy with webers etc

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If the only thing that you've changed is the fuel pump then it suggests it's a fuel pressure issue. So that leans towards fuel pressure regulator mounted on the fuel rail. EFI fuel pressure is normally about 40 psi. I checked Linton's link about and it's 36 PSI for the 280. So that's what I'd check first. If you have access to an EFI fuel pressure gauge then that'd be an easy test.

 

The fuel regulator  has a fuel in, out and a vacuum line. The vacuum line is very important. The fuel pressure at the injectors has to be maintained constant through all engine conditions i.e. high vacuum and no vacuum. The vacuum line makes the adjustment as needed to keep the fuel pressure constant. If the vacuum line is not on, then at idle with higher engine vacuum the fuel pressure relative to the manifold pressure will be higher than it should be resulting in a rich mixture at idle. This would be my first check.

 

A faulty engine temp sensor or AFM meter could also do it, but if they were ok before, then less to now be faulty.

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Righto thanks, i had checked Linton's link about fuel pressure and I have replaced all of the vacuum hoses, plugs,leads, all fuel lines from the hard pipes forward including the fuel rail on the engine already, I'm waiting on a new dizzy from the states and a new fuel regulator from sydney, The temp gauge is working and temp is steady with new radiator and thermostat fitted, I think the thermotime switch is under the temp sender but i haven't the foggiest what it does or if it can cause rough running. The AFM has a big question mark over it, as under the plastic cover it looks like hell and the electrical pins on the AFM don't look much better, I will post a WTB ad for a replacement.........thanks for the advice, all i can do is wait for parts and try for another AFM. I will post again with THE FIX!

 

I have just finished reading Linton's link to the EFI bible and what a great bit of gear that is, heartily recommended to easily explain the mysteries of EFI and answered my question in plain english about the thermotime switch, so a big thank you to Linton

Edited by cruza

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Hi,

 

I have a copy of the factory ws manual for the Z injection system.

It is a very easy read and has good section on trouble shooting.

 

If you PM your email address I will send it to you.

 

Cheers.

 

PB

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look down the bottom of page under reference: efi bible in pdf I found this to be a very good resource

Hi Linton,

Thanks for osting this link, another great resource for the EFI system.

 

Cheers

 

PB

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PM sent to PB        Thanks for all suggestions, Just to recap, New Dizzy and cap,leads and plugs, timing done, compression on all cyl between 155 and 165 psi, new fuel regulator @36 psi, unmolested AFM fitted, all injector leads tested, all vacuum and fuel lines plus fuel filter replaced, cold start injector disconnected for the moment, new intake manifold gasket fitted (old one failed the wd40 spray test)  From cold it turns over once, starts, and idles, and is still a bit rich, AND it still has a slight miss on one >:( :o :( cylinder, so now i think its down to a bad injector or ECU.........I'm now bald, with a alcohol dependancy problem, but i still love my Datto.

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Hi Mate

 

Have sent you a copy of the manual.

Let us know how you go.

 

Cheers

 

PB

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