crosseyedrob Posted March 18, 2015 Share Posted March 18, 2015 Hello, I'm struggling to get my l28 running properly. Cranks and warms up well, but once at operating temp it stumbles under load almost like in a limp mode or something. Recently replaced injectors, injector plugs, rebuilt distributor, coil, coolant temp switch, fuel rail. Connections all appear to be secure. Removed coolant bypass system. Played with timing seemed to help at first but once at operating temp makes no difference, will rev but under load it stumbles and struggles. Any help would be great, thanks in advance Quote Link to comment Share on other sites More sharing options...
stravi757 Posted March 18, 2015 Share Posted March 18, 2015 Have you checked for vacuum leaks? Try turning the idle screw on the throttle body all the way down once its warmed up. That will help you find any vacuum leaks after the throttle body. Quote Link to comment Share on other sites More sharing options...
crosseyedrob Posted March 18, 2015 Author Share Posted March 18, 2015 Haven't found any leaks. I'll try throttle screw , am I primarily listening for leaks around vac hoses? Quote Link to comment Share on other sites More sharing options...
stravi757 Posted March 18, 2015 Share Posted March 18, 2015 Yes listening for leaks. Also when you turn the screw all the way down, the engine should die once the car is warmed up. Quote Link to comment Share on other sites More sharing options...
crosseyedrob Posted March 18, 2015 Author Share Posted March 18, 2015 Thanks for the help, I'll try this Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 18, 2015 Share Posted March 18, 2015 Many old L28 EFI systems are lean. For whatever reason, old electronics, or today's fuel, adding resistance to the coolant temperature circuit can fix the problem. Actually, it seems that Nissan might have set the EFI tune on the edge initially, especially for the ZX's, for mileage or emissions reasons maybe and now it's too lean. It's not uncommon to find a resistor in the coolant circuit wiring on an old ZX. Many people add a potentiometer to tune on the fly. Search for BRAAP's EFI tips in the L Series FAQ's and you'll see it described. Quote Link to comment Share on other sites More sharing options...
crosseyedrob Posted March 20, 2015 Author Share Posted March 20, 2015 Tried the throttle screw test, the engine doesn't cut off nor can I find any leaks. May try the potentiometer just need time. Quote Link to comment Share on other sites More sharing options...
grillhands Posted March 22, 2015 Share Posted March 22, 2015 I had this before. I unplugged the coolant temp and it ran great Quote Link to comment Share on other sites More sharing options...
malibud Posted March 22, 2015 Share Posted March 22, 2015 Clogged fuel tank/ line ? That's been my problem on a few ... Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 22, 2015 Share Posted March 22, 2015 Played with timing seemed to help at first but once at operating temp makes no difference, will rev but under load it stumbles and struggles. If you're new to the old Z EFI system, the fastest way to get them running well, ironically, is to spend the time to go through all of the tests in the Engine Fuel chapter, or the Fuel Injection Guidebook, and give it a Tuneup to spec., before playing with anything. The playing usually just screws things up. The hunt and peck method never works. All of the components and their connections need to be in proper working order. Once you have fixed them all and know they're right, then you can make the minor tweaks to compensate for old parts, or modern fuel. 1 Quote Link to comment Share on other sites More sharing options...
crosseyedrob Posted April 5, 2015 Author Share Posted April 5, 2015 (edited) Been out of town, finally tried some stuff. Coolant switch unplug did not change anything, new fuel system everything. Did fsm ecu plug test and afm pins 6-8, 6-27, 8-7 didn't ohm out, I assumed afm may be bad. ran afm resistance test off the car and on the car, and all ohm numbers are good. Checked individual wires for continuity and all checked good.Is the afm bad? Edited April 5, 2015 by crosseyedrob Quote Link to comment Share on other sites More sharing options...
Datsun#1 Posted April 15, 2015 Share Posted April 15, 2015 Sounds to me like your TPS has gone bad.replace that and then PM me if you have any more questions. Quote Link to comment Share on other sites More sharing options...
Datsun#1 Posted April 15, 2015 Share Posted April 15, 2015 Also,stubling under load can be a bad EGR as well.check to make sure your EGR valve diaphragm isnt broken.they tend to go bad after 30 years.is it backfiring? Quote Link to comment Share on other sites More sharing options...
Gavin Posted April 18, 2015 Share Posted April 18, 2015 Checked the fuel filter? My orange car drove me nuts with this, turned out to be a layer of rusty sediment in the pristine looking tank. It'd clog a new filter in minutes. Quote Link to comment Share on other sites More sharing options...
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