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1976 280z idles fine but under load no power

Old 01-11-2008, 08:23 PM
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1976 280z idles fine but under load no power

Hi guys this is my first power and I'm glad to be a member of this board.

I tried searching for a solution to my problem but was not able to come up with anything.

My car is a 1976 280z with the stock fuel injection system and it has an N47 head. I bought it from a guy who had it sitting for a long time it wasn't running. Now I've got it running and it drove fine the other day but after I had the fuel tank cleaned it has no power, when I floor it nothing happens.

Here is what I have replaced since I have had the car:
New Fuel Pump (I have 34 psi at idle and when I dead rev it has 40)
New Fuel Filter
New Fuel Injectors & Connectors
Just cleaned tank
New Fuel Lines
New Spark Plugs
New Distributor Cap & Rotor
Cleaned all connections with cleaner (QD Electric Cleaner)

Also, the coolant temp sensor is working correctly I check it as stated in the manual. It dead revs fine but under load it won't move past like 10-20 mph.

Any ideas? I appreciate your help.

Thanks,
KC
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Old 01-11-2008, 10:37 PM
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was going to say check the fuel press but you did. hmmm, thats strange. when i changed my exhaust/intake mani gasket i also had a freak loss of power, it would sorta dead rev ok, but it would sit on its face when drivin. i would say, go over EVERY SINGLE LAST EFI connection with a wire brush, electrical connector cleaner, and a little tiny *** flat head screw driver or a thinnish nail and re-bend all those spade like connectors (the metal flappy looking ones) inside the actual plug. just spraying isnt always good enough. do this on the ECU as well. just dont get the ecu itself to wet.
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Old 01-12-2008, 04:12 PM
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Welcome to Zdriver!

So it was running fine, you cleaned the tank (and that's the ONLY thing you did?) and now it has no power?

I suggest pulling your spark plugs & look at the tips. You may have a clogged fuel injector.
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Old 01-12-2008, 06:07 PM
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I checked the plugs and it looks like it's running rich (a little dark) but they are all even. I will pull all injectors and check it they are flowing ok. Thanks for the suggestions.
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Old 01-21-2008, 10:28 AM
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I found the problem. When I unplug the TPS the Z runs MUCH better. I wouldn't say it's 100% but it's close.
So I tested the TPS with a DMM like the manual says to and it seems to operate fine. I took it apart and cleaned the contacts and checked that everything moved smoothly and I can't find anything wrong with it. With it back on the car the problem is repeatable: if I plug it in the car runs poorly, if I unplug it the car runs better.

So does anyone know what the problem is now? I don't want to leave it unplugged because it doesn't seem to run as well as it had in the past. Besides, I want to fix the problem, not just work around it.

Thanks guys
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Old 01-22-2008, 08:57 AM
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You're sure the wiring to the TPS is in good order? Just because the senseor is working, doesn't mean that the signal is not diminished by the time it reaches the ecm.

But, I always start with the basics. Compression, Timing, Spark and Fuel.
Find out which variable is off, and work your way to the problem. No matter how complicated the vehicles system is, it still operates on the same physics as a Model T Ford.

Before you said TPS, I was seriously thinking you had some timing issues.
Still worth a check. Because depending on TPS, and your RPM's, the car will advance or retard the timing and change the fuel injectors. If timing is off, it may work great with no load, but run like a three legged dog under load. Check the basics first. Don't get complicated until you are sure the problem is complicated.
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Old 01-22-2008, 11:00 AM
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Just a thought: Check out page 14 in the EFI Bible (PDF, the link's around here somewhere if you don't already have it). Unplugging the TPS would eliminate the acceleration/full throttle enrichment circuit (i.e. lean it out). If your plugs are saying you're running rich, then the unplugged TPS would offset that, but it would be masking the problem more than fixing it. If all the plugs are looking rich, have you tested to see if you have a leaky or stuck-open Cold Start Valve? If it's only one or two of them looking rich, a particular injector or two might not be closing all the way between pulses, or have bad spray patterns (more like a stream, less like fine spray).
Keep us posted on progress!
Dave
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Old 08-27-2015, 03:52 PM
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Did you find the problem? Mines having the same problem.
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Old 08-28-2015, 07:02 AM
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This thread is from 2008, and with the OP only having 4 posts, I'd say they've moved on. Case closed.
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