tech9 Posted October 4, 2008 Share Posted October 4, 2008 Bought a new Z this weekend, having a little trouble figuring out the problem with the engine. I did drive it home, which was over 30+ miles away, and it did have a little problem with acceleration but once you got on the highway, around 50 mph it wasn't as noticeable. Starting off is real bad, backfire, etc. Here is what I tested: ignition module, coil, checked tps, checked afm, all see good. Checked the manual and it said the same things I checked, which all see to be working (swapped off a running l28). One problem I see, when hooked to a fuel pressure gauge, is that its losing pressure when the car is off. Maybe the regulator is causing all this? Any help is appreciated, thanks! -Joe Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 4, 2008 Administrators Share Posted October 4, 2008 Dropping fuel pressure with engine off does not necessarily have any thing to do with the hesitation/misfires while the engine is running. These cars and all its components are quite old now, and most won't hold fuel pressure when the key is turned off, like they did new, which is OK and shouldn’t affect how the engine runs. Unless adequate fuel pressure can't be maintained while the engine is running. To rule out the fuel pressure regulator, clogged fuel filter, clogged fuel pump inlet screen, bad fuel pump, (and anything else that could affect fuel pressure), you need to verify that you have adequate fuel pressure under ALL conditions while the engine running! Preferably when the engine is acting up, is the fuel pressure adequate? Quote Link to comment Share on other sites More sharing options...
tech9 Posted October 5, 2008 Author Share Posted October 5, 2008 I did check the fuel pressure while it was misfiring, it goes around 30-40 psi, which seems enough. I'm going to pull the valve cover and check if there is any valve / rocker damage. Quote Link to comment Share on other sites More sharing options...
tech9 Posted October 13, 2008 Author Share Posted October 13, 2008 Main problem was the distributor, swapped with a good one, and ran 100% better, still something else causing slow acceleration, but after inspecting old dissy, it was missing bolts, someone stripped others, etc. Quote Link to comment Share on other sites More sharing options...
woldson Posted October 13, 2008 Share Posted October 13, 2008 Great trouble shooting there! Quote Link to comment Share on other sites More sharing options...
VinhZXT Posted October 15, 2008 Share Posted October 15, 2008 symptom: the fuel pressure doesn't hold in the line problem: the check valve at the fuel pump is not working. Quote Link to comment Share on other sites More sharing options...
tech9 Posted November 11, 2008 Author Share Posted November 11, 2008 Ok been messing with this car a lot this weekend. Swapped in a 280ZX dissy, that corrected what I thought to be most of the problems, but not much. So I threw out thinking the ignition module could be bad, etc. I swapped from a working Z, maf, computer still no dice. I took off valve cover, did a valve adjustment, compression test (all around 90-100 cold) all the mechanical on the engine look fine. Drained the old gas, dropped in some 91 octane, plugs have carbon on them so I think all the wires are firing correctly. I tried to set the timing as per the service manual, but at 10 degrees (as the book says) it actaully runs worse then before. High rpms seem almost no missing, but low rpms have a hickup. You can drive it down the road to test, and it will make it, just very slow acclerating. I know i'm missing something stupid maybe, any hints? TIA Quote Link to comment Share on other sites More sharing options...
tech9 Posted November 16, 2008 Author Share Posted November 16, 2008 Yet another update, if anyone is listening I took off all the injectors, tested and cleaned them. They have a funky pattern on most of them, could this be the problem? Weird thing is I put new plugs in, checked them, and only the middle 2 of them are clean, the rest are black. Quote Link to comment Share on other sites More sharing options...
woldson Posted November 17, 2008 Share Posted November 17, 2008 What do you mean by "cleaned them"? Quote Link to comment Share on other sites More sharing options...
tech9 Posted November 17, 2008 Author Share Posted November 17, 2008 Someone posted and said to let them soak in injector cleaner, hold them open and spray cleaner through, etc, etc. I'm sure it don't help if the injector is just worn out or dirty fuel was ran through them. They actually did have a little better pattern it seemed, but its still pretty 'streamy'. Going to swap out known good injectors and we'll see. Quote Link to comment Share on other sites More sharing options...
tech9 Posted December 28, 2008 Author Share Posted December 28, 2008 Update: New injectors did the trick. Runs like new, just need to do a little timing adjustment and we should be golden. Now I can finally start getting it primed for paint. Quote Link to comment Share on other sites More sharing options...
woldson Posted December 28, 2008 Share Posted December 28, 2008 Congrats! It is not easy to remove the deposits from injectors. Quote Link to comment Share on other sites More sharing options...
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