Daniel13brx7 Posted March 5, 2011 Share Posted March 5, 2011 So today i drove to work in the morning and the car ran fine. When i was going to leave work the car wouldnt start. It would crank over really fast and all i would smell is fuel. I encountered this problem a while back with an old afm that the flap would stay stick open. Soi check the flap everything is fine. I check for spark, got it. Fuel for sure i was getting. What i find very odd is that if i disconnect the fuel pump the car starts and idles. If i rev slowly it still stays on. As soon as i plug the fuel pump back on it floods and turns off. My guess the afm sending a full throttle signal to the injectors? I tired 2 different afm`s now. Neither helped to start the car. Could it be the CAS? But i doubt it since the car runs w/o power to the fuel pump. Any ideas guys? Should i try a third afm before i open a can of worms and rule out other things that might be the problem? Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 5, 2011 Share Posted March 5, 2011 Fuel pressure too high? If you have an aftermarket pump and a blocked line or regulator, pressure can get very high. Temperature sensors lost continuity, sending "cold, give gas" signals to the ECCS? Quote Link to comment Share on other sites More sharing options...
Nizm0Zed Posted March 5, 2011 Share Posted March 5, 2011 just for the sake of ruling it out, could you try a different ECU? Maybe you can borrow one, it'd only take a minute to swap over and test it once you pull the trim panel off. I doubt its the AFM itself, if you have all ready tried 2 other ones. Yes, maybe the temp sensor registering a cold motor all the time, but it should still start and run (especially if cold) it'll just be heavy on fuel. How long does it run with the fuel pump unplugged? It shouldnt run at all with the pump unplugged, if anything, only for as long as the residual pressure stays in the fuel rail. Quote Link to comment Share on other sites More sharing options...
Daniel13brx7 Posted March 5, 2011 Author Share Posted March 5, 2011 Hmm... Which one of the two sensors on the therstat housing is the temp sensor? i let the car run yesyerday gor about 15 mins idling normally with the pump unplugged. Then i slowly began to rev the motor and got it up to 5000 before it cut out abit. Plugged in the pump while it was still idling and instant death again. One time i managed to keep the car running after i plugged in the pump but as soon as i touched the throttle again just instant flood. Sadly i dont have an extra ecu or know anyone around that can lend me one just to rule it out. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted March 6, 2011 Share Posted March 6, 2011 (edited) Sumting stwange? 15 minutes without a fuel pump!? That is a mystery in and of itself. My first guess is that you blew out the FPR and fuel is just running via gravity, or more likely siphon if your check valve in the pump is open. Edited March 6, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 6, 2011 Share Posted March 6, 2011 (edited) I haven't seen an 81 in person, let alone an 81 turbo, but don't most Zs have pumps wired in using studs with nuts. What is this plug that is being unplugged to disconnect your fuel pump? Or are you unplugging a relay? Do you have a picture? Edited March 6, 2011 by NewZed Quote Link to comment Share on other sites More sharing options...
JSM Posted March 6, 2011 Share Posted March 6, 2011 (edited) You need to really install a Fuel pressure guage inline and see what your fuel pressure is. These used to be like $15 but work very well. Use the silver "T" and leave it inline. http://www.harborfreight.com/fuel-injection-pump-tester-92699.html Edited March 7, 2011 by JSM Quote Link to comment Share on other sites More sharing options...
cgsheen Posted March 6, 2011 Share Posted March 6, 2011 Hmm... Which one of the two sensors on the therstat housing is the temp sensor? The L28's don't use EITHER of the temperature sensors up front in the thermostat housing for EFI. One goes to the coolant temperature gauge, the other is the "thermotime switch" which runs the Injector Fan at shutdown if the coolant is above a certain temp... The temperature sensor your engine DOES use is the Cylinder Head Temperature Sensor which is in the side of the head, passenger side, closer to the firewall than the radiator, and it should have an electrical connector the same as the connectors on the Injectors. i let the car run yesyerday gor about 15 mins idling normally with the pump unplugged. Then i slowly began to rev the motor and got it up to 5000 before it cut out abit. Plugged in the pump while it was still idling and instant death again. One time i managed to keep the car running after i plugged in the pump but as soon as i touched the throttle again just instant flood. No way in hell my turbo motor runs for more than several seconds with the fuel pump killed! (I know, I used to have a switch in the fuel pump power lead and could turn it on and off from the cockpit) As per usual, you should check and clean ALL of the electrical connectors on the EFI Harness (actually ECCS Harness...) and the troubleshooting guide / diagrams in the FSM for the '81 280ZXT are really good and fairly easy to follow in testing fuel and ECCS components. I had a complete, running '81 ZXT for a time as I was doing the L28ET swap into my '74 260... Quote Link to comment Share on other sites More sharing options...
Daniel13brx7 Posted March 6, 2011 Author Share Posted March 6, 2011 I haven't seen an 81 in person, let alone an 81 turbo, but don't most Zs have pumps wired in using studs with nuts. What is this plug that is being unplugged to disconnect your fuel pump? Or are you unplugging a relay? Do you have a picture? im disconnecting the power to the fuel pump in the hatch area. By unplugging a 2 wire clip. I normally do this as a theft deterrent. If my car tries to get stolen it wouldnt go anywhere since it would only run for a few seconds. Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 7, 2011 Share Posted March 7, 2011 Odd coincidence - I just replaced the fuel rail on my 76 last night because the stock multi-piece unit had started leaking at the hoses connecting it together. Started it up and it sounded really rich, realized that I had hooked the FPR up backwards so I turned the fuel pump off to bleed the pressure down while it was running so that I could swap the hoses. It ran for about 10 - 15 seconds!, which feels like a long time when you're waiting and wondering when the engine is going to run out of fuel. I have an aftermarket Airtex pump, rated at ~70 - 95 psi, so my fuel rail was super-pressurised and the fuel had no where to bleed off to. If your 15 minutes is really about 15 seconds, you might have a blockage in your return line, or a clogged FPR. Quote Link to comment Share on other sites More sharing options...
Daniel13brx7 Posted March 7, 2011 Author Share Posted March 7, 2011 You guys are not going to beleive it. It was the dumb afm! I picked up a third unit just out of curiousity. Plugged it in and bam. Started right up. Ive now gone through 2 afm. What could be making them go bad? Quote Link to comment Share on other sites More sharing options...
Daniel13brx7 Posted March 7, 2011 Author Share Posted March 7, 2011 I noticed with the bad afm's plugged in the car would run w/o power to the pump. Right now with this working afm if i disconnect the power to the fuel pump it only runs for a few seconds and then the motor just turns off. Quote Link to comment Share on other sites More sharing options...
misterZ Posted March 7, 2011 Share Posted March 7, 2011 (edited) You guys are not going to beleive it. It was the dumb afm! I picked up a third unit just out of curiousity. Plugged it in and bam. Started right up. Ive now gone through 2 afm. What could be making them go bad? Wow, really? What year is your Z? I was going to pipe in as I have similar issues and suspecting the Fuel Injection Relay (75-77 only) that sends the pump signal thru the AFM. I replaced three AFMs and the ignition switch to no avail; however, the best troubleshooting tool for fuel issues is installing a gauge between the filter and rail (as above). I found I was getting fuel w/ key in 'start' but not w/ key in 'on' position. Subsequently, the engine will start and run only long enough to exhaust the fuel in the rail. If I have someone start the vehicle and hold the key in the 'start' position while I disconnect the wire to the starter, pressure stays up (pump on) and car will run until key returned to 'on' position (pump dies). What a friggin' gremlin this is... but another member is shipping me a relay for troubleshoot/replacement so we'll see if my suspicions are correct. EDIT: (added) I got my gauge for ~$25. (here or on Ebay) and bought the tee from Home Depot for $1.80 and (2) 1/8" nipple barbed pipes from O'Reiley's (another ~$5.)--gauge is permanently installed in-line. Edited March 7, 2011 by misterZ Quote Link to comment Share on other sites More sharing options...
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