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Low RPM Stumbling


PETEW

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Hey Guys,

I finally got to pick up the 280ZXT donar car today. I changed two injectors that were incorrect with the turbo injectors that Len supplied me with (thanks Len :D ) and put in a new set of NGK spark plugs. I started it up and it fired up right away. The car runs pretty good at idle, a little rough, but not a big deal. When you take the car out cold it runs very rough from idle to 3K RPM. It would back fire and jump until it got to a RPM it liked. All the backfires were early on in the exhaust. When the turbo has 0 pressure it starts to clean up, if you have boost it runs very good. When we got the car fully warmed up, that took forever (I'm guessing a bad thermostat), it seemed to run even better. It still would stumble at idle to 2K RPM, but once the turbo had 0 to positive pressure the car pulls nice. It doesn't seem to matter if you get on the gas smooth and easy or just mash it, it seems to stumble in the beginning. When the car is warm it does not backfire any longer, it just stumbles. If any of you have an idea of the problem would be give some ideas, and I'll start to look. We were thinking it might be the AFM or maybe a sensor that retards the ignittion for the turbo not working. Help bonk.gif:confused: Thanks guys.

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So far I've looked into the EGR and looked at the timing. Stupid haynes manual tells you how to set timing for the '81 Turbo and the 82 and higher it just says see your dealer fmad.gif . We took the timing light to it and did just a little. It seems to be running better, but I have a feeling that the AFM needs to be adjusted, I also have a feeling that the FPR is not working right, I need to get a fuel pressure gauge for that. confused2.gif Thanks for the thought. Hopefully we'll figure it out.

 

Pete

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PETE

A fuel pressure gauge is indespensible. You can even modify an old freon gauge setup; that you can buy at a pawn shop. Or bite the bullit for around 35 bucks and buy one. Hook it up after your fuel filter run a long enough hose so you can close your hood and stick it under your wiper to see it so you will know your press. at boost. That may shed some light on the subject.

Hayes manuel is really not to complete. If you can attain a 83 280zxt factory manuel you'd be better off. I believe you can get a CD of one off curtesyparts.com.

Wish you luck! 2thumbs.gifcheers.gif:D

Len

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Guest Anonymous

Ive been trying to get a FSM for my 83 280zx but no place has them but Ebay. If you get one let me know where you got it from. PLEASE! :confused:

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We'll I've tried adjusting the AFM and it didn't really do too much. I am going to get the fuel pressure gauge and see if the pressure is ok. I was thinking spark might be an issue too, but why would it work good under boost, but not at lower RPM's. bonk.gif I also checked compression again, just to make sure, and I am getting 140 on every cylinder. The engine is definitley good, I just need to figure out what is causign the initial stumble. Oh well, if I figure it out I will let you guys know. Thanks.

 

Pete

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  • 2 weeks later...

Do yourself a favor and spend the extra couple of bucks on the 1.5" diameter VDO fuel pressure gage. I had a Jegs one and it was VERY unreliable. Just one data point there, but the VDO one is easy to read (white face, black markings) and seems to be a quality piece (not surprising as VDO is known to be the good stuff).

 

Trouble shooting with no pressure gage is tough enough - trouble shooting with a junky gage might even be worse.

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Here is the latest update on the turbo saga. I replaced the crappy wires on the car and checked the cap and rotor, both were actually new. I then started to check sensors. The TPS wasn't working right so we adjusted that. I also checked the O2 sensor and that seemed to be getting some weird readings. I bought a new one since I was going to rplace it anyway with the new downpipe. Well the changes still haven't cleaned it up. It runs better down low but it still needs some work. I will let you know how the fuel pressure testing goes. ;)

Pete

P.S. Where are you guys getting your fuel pressure gauge, the ones I have been seeing are for schrader valves, or GM specific.

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