1990 300zx NA running rich need help

[godswrath84657]

Ive been fighting with this car for quite a while now so ill list the things that ive done so far... the PO did an engine swap so im not sure what else was jacked up

It originally had very little power and was eating gas like crazy and finally figured out the timimg was off by like 15 degrees. Adjusted the timing and now has good power but is still eating gas. About 150 miles to the tank! No smoke out the exhaust but smells really rich in the cab. At startup theres some smoke by the firewall but the it stops after like 5 mins. Egr valve has been removed.


No ecu code
Checked o2 sensors with the ecu
Injectors ohm out
Compression was all the same
Replaced the MAS
Idles at about 1k
Aftermarket headers and cat back exhaust were put on by PO


Please let me kno if you have any ideas or suggestions
Power balance test was good

[t.mcginley.jr]

First, do you know anything about the O2 sensors, like how old they are or what brand?

Second, you should check fuel pressure after the filter. It should be around 43 psi at idle.

A bad coolant temp or fuel temp sensor will cause poor mileage too but that almost always throws a code. I'd replace them anyway since they're so cheap.

[nissanfreak12]

What Jr said, I would also be concerned with a pinched o-ring at one of the injectors, especially with that bad of gas mileage.

Check for a vacuum leak, that could also cause poor mileage.

[godswrath84657]

Thanks for the responses and no I dont kno anything about the o2 sensors. And I checked the fuel pressure and I think it was around 35psi and ill order those sensors and replace them.

And 99% sure its not a fuel leak. I replaced all of the orings and gaskets for the fuel rail myself. Also I sprayed starter fluid all around and didnt notice anything.

I do have a question about the timing tho. There are two wires by the radiator where u check the timing and I was wondering what the difference between the two are? The readings between them is about 15 deg apart. I picked the one that seemed to run better but I cant quite adjust it to right on 15deg. Its more like 12 and I cant turn that thing on the right any more.

[nissanfreak12]

Its not the leak outside you should be worried about, well is it is but not when it comes to a pinched o-ring. Its extremely easy to pinch an o-ring when putting in an injector, did you use any lubricant to slide them in?.

At 35psi either you have a leak, weak pump, or fuel pressure regulator is bad. Strong fuel smell is not a good thing in the cab, that usually means you have a small leak. The fuel is going somewhere, just need to find out why and if your only getting 150 per tank, that about 9mpg, it will smoke black if its unburnt fuel.

Take the vac line off the FPR, any fluid? Does it make a diff to the pressure when you disconnect?

Have you checked the seal for the tank? Hoses from the tank to the fuel filter? The little hose that seperates the fuel rails from the left and right side?

[nissanfreak12]

[quote="godswrath84657"I do have a question about the timing tho. There are two wires by the radiator where u check the timing and I was wondering what the difference between the two are? The readings between them is about 15 deg apart. I picked the one that seemed to run better but I cant quite adjust it to right on 15deg. Its more like 12 and I cant turn that thing on the right any more.[/quote]

Do not use those wires, they tend to be, well unreliable. You want to use the wires that are going to the #1 coil. The most accurate. They can be a PITA to get a reading sometimes, but its the most accurate place.

[godswrath84657]

Yes I used just vasoline to put the injector rings in. And will try all of those things to try and find the leak and maybe take the injectors back out to make sure they're good. Theres definately no black smoke in the exhaust.

I tried to take the timing off the first coil but I have an inductive type timing light and couldnt get a reading at all... suggestions?

[nissanfreak12]

Peel the harness back and try an get just the black? wire in the loop of the the timing light. You will have to mess around with it till it works. You should only have one wire in the loop for it to work.

[t.mcginley.jr]

If you can't get anything off the first coil pack wire, try putting the pickup around the PTU subharness.