racebird1

When all is the way it is supposed to be it will run very well without adding extra cooling fans or higher fuel pressure. If it is running rough at restart something is wrong. Make sure the fuel pressure is correct and the fpr is letting the excess fuel return back to the fuel tank( and there should be fuel returning). If the fuel is vaporizing then it is running too hot because when everything is normal this will not happen. You can try pulling out the fuel rail with the injectors and placing the rail into a large pan and crank the engine untill full pressure is reached. While doing this make absolutely sure that there is no source of ignition or you will start a fire. Check the spray pattern while you are at it and then make sure the injectors are holding pressure and not leaking down. Just because they were replaced does not mean that they may still have an issue. I also noted that you put grease or oil on the orings be careful what you use because some greases will attack the rubber.

Well the AC stopped working I pressure tested the system before evacuating and charging. I charged the system and after a few days I believe the freon is low. The clutch still engauges but no cool air now. I did not replace the cap after I charged the system because I knew I was going add more freon. The question is, will it leak from the low side valve if you don't put the cap back on? Is the cap there to seal the valve?

Even though it is working I am still curious about the pressure switch. The factory manual I have specifically states that the switch is to protect the system from abnormal buildup of high pressure. I can't test the switch to see if it is open or closed at low pressure now because I have freon in the system. According to the wiring it is in series with the Thermostst and the micro on / off switch and all three needs to be closed to send the curent to the relay which then sends power to the Compressor clutch. I know it shouldn't matter now that it is working but I just like knowing exactly how things work.

I got it working Just in time for the current heat wave. It turned out to be a bad relay. I still have a question about the low pressure. Is there a low pressure switch because the manual states that the pressure switch on the drier is to protect the system from high pressure. That switch only has two wires so I don't understand how it can see too high and too low of a pressure. There is no other pressure switch only the thermostat and a micro switch which is only a switch connected to the lever when you turn on the AC. I only have one 14 oz can in the system and the sight glass is full of bubles but the air is ice cold. It's probably the first time anybody was glad to see bubles in there sight glass but at least that means the compressor was working.

I have searched hear and can't find what I am looking for so hear is the question. I have pressure tested the ac system and it held 80 lbs pressure. I evacuated the system to -30" for 1 1/2 hours and put one 12 oz can of r-12 in system and the gauge is showing 80 psi and I can't seem to get the compressor clutch to come on. I have 12 volts to the pressure switch on the receiver / drier. Does this power come in from the micro switch and thermostat or does it go there after the pressure switch. I tried to jump out the PS pins at the connector but still did not come on. Does it need a certain minimum pressure in the system before it will come on and if so what tells it what the min pressure is. I know it still does not have the reccomended amount of r-12 in the system yet but I don't want to put the rest in if something else is wrong. Thanks AC is not my specialty.

I finally got back to the Z today and did some more checking. I found that the cold start injector is not injecting. I pulled it out and checked it when my son started the car and nothing. It put my injector tester lead to it gave it power and it works fine but not when I start the car. I will need to look into the thermo time switch. I tested the main injectors a litttle differantly, I pulled the fuel rail and and turned the key to on and fingered the AFM enough to get the pump on then powered up the injectors up one by one and they all sprayed great so I don't think the injectors were bad after all. I installed the new ones anyway. I advanced the timing to about 25 degrees cold and the vacuum went up to 18 inches but the engine races too much so I backed it down to 20 and I don't get any intake backfire. I also fingered the AFM all the way when it was running and it bogs down the engine from being too rich so I think that is working fine as well. I will install the pot switch this week and see if that will help.

As you may not know the fule pump signal runs through the air flow meter so it will only give you voltage while the engine is cranking or starting. The flap needs to be sucked open slightly to close the switch in order for the pump to run. This is a safety feature in case there was an accident that would stall the engine and with the key switch still on and if ther was a leak it would continue to pump gas. That is why they ran it through the afm. If you have your cover off of the afm and you open the flap a little with the key switch to on I would think the pump should run.

You may also have other issues that are contributing to your problem. Your air flow meter boot has tons of duct tape on it which tells me it must have large cracks in it. You will need to replace it you cannot have any leaks in the air and vacuum system. Those arn't too expensive you can find them on e-bay. Good Luck

I haven't had any spare time to get some of the changes to the car done yet this week so I can see if anything improves. My new E-bay injectors arrived today, that only took three days to get here so hats off for good service and the hoses are plenty long enough and I will even need to shorten them because they have about 3" of hose on them so naturally I was glad to see that. They look great and I hope they work as well as they look. My potentiometer my be here as well so soon as I get time I will try these changes and see how it goes.

Hey blue the calibration method took a ton of time to produce and I really appreciate the time you put into it. I will be using to the pot adjustment and I have one on order and should have it in a day or two. I have not decided where I am going to put it yet. Mybe temporarily under the hood then move it to the ECU area. I am going to order the new injectors so I can be sure that they are giving me the right amount of fuel. The two older afms don't have the serial number on them but both newer ones do. I am going to try one of the older ones since one of them was from the car and I have it calibrated to Blue's method. Since I am so close to it running pretty decent now these changes should get me where I need to be for awhile.

I have been going through all the afm tests on the four afm's I have. Two are older much heavier with the back flow valve which are probably from the 76 and two are much lighter and might be a newer version. I did the weight tests with the measured water and the two with the glue missing were way off and one of those was completely sprung. It took about 13 teeth to get it back from fully sprung. The one that was on the car was still glued but was comomg up a hair too tight which is towards a lean fuel mixture which is also part of my problem. I will attempt to go with a setting of just below normal to try for more fuel. I then did the reccomended cleaning of the contacts and such with testing before and after the cleaning and some of the tests it did make a difference from cleaning. Here is the thing, I tested the ohm readings as per instructions and they all passed after the cleaning but I noticed that if I did a more detailed test of the ohm test of the carbon trace the two newer ones came out almost exactly the same and the two older ones came out almost exactly the same but the new compared to the old are a little differant. I measured the resistor strips right on the board so I was getting an accurate reading. I have concluded that there is some difference between newer and older 76 version but I don't really know if it is enough to change anything? The other one with the glue still on the screw was just about right on with the weight test. The fully open weight test is a little tricky because of the friction of the string dragging and the angle really doesn't allow the flap to fully open it is just shy of open. I am going to get a new set of the injectors and see if I can set the afm and timing to get me through the summer.

I was looking at those injectors and I thought I saw somewhere in a post where they did not think they worked too well but maybe they had other issues. How are they working for you? I did not see any negative feedback. The AFM link was great just what I was looking for thanks

Do you use fuel hose rated for fuel injection from a local parts store or get special hose somewhere? I used some from a local store a while back and it didn't hold up all that well.

When I pulled the plugs I checked them all out and found that it is indeed running very lean. All the plugs have a white coating on the electrodes. I have ordered a 5k pot to try on the temp sensor but I also looked at the three extra AFM's and they all have a differant resistance of tension on the flap and I don't really know which one was on the car. I searched the site and can't find out how to tell if it is at spec or how to set it there. Does anybody know how to do this? I am sure they must set them by how much tension it takes to open the flap. I can turn the wheel but to what? I still think I need to pull the injectors again to make sure the screens are clean. A local injection company says they can rebuild them in two days for $20 each. It bothers me a little that all I get from them is a steady stream not any kind of spray. They al trigger fine with no sticking or leaking. The $20 each does not seem too bad.

I had my friend over with the scope and we put it in through the spark plug holes and checked out the condition of all the cylinders. All the cylinders have avery good cross hatch pattern on the walls and very little carbon on the pistons, now this isn't going to tell me what condition the rings are in but I would think that an engine with such a low compression would no longer have cylinders that look so good. I should probably take the valve cover off and make sure the valves arn't a little sticky. Never the less untill I can find a fix I have been looking for someone local to possibly rebuild my engine. I just don't have the time right now to do it myself. I will in the mean time try to find some simple instructions to vacuum time and put the potentiometer in to see if they can help get it through the summer. Anybody have simple quick instructions on the vacuum timing method. Do I simply turn the distributor untill I get the highest vacuum?

I have a pretty good history on the car and who owned it since new. I am pretty confident on the milage which was confirmed with the condition of orther components of the car. The cam shaft shows no wear at all and the oil pressure is very good. I am wondering if something may have happened to the rings or cylinders from sitting so long. A coworker has a camera I can stick down the cylinders through the spark holes to see if anything is going on with the cylinders. I will even be able to tell if there is any cross hatch left on the walls. I put some mystery oil in the cylinders and when I go to start it up later today I am going to get a quick vacuum reading and see if that comes up from the higher compression from the oil being in there. Either way if it stays this low is there anything I can do to get it through the year with out the intake backfire and tackle the engine next year? Does it even pay to do the engine myself I see them on ebay for maybe under a grand over what it would cost me to do it myself?

I re did the compression test on number 2 and 5 with throttle wide open and air filter out and you were right absolutely no difference. Then I did a wet test on those two cylinders. On #5 I put about three squirts of 5-20w oil in and tested again and got 147 psi then I proceeded to #2 and put about 6 or 7 pumps in and checked it and got 190 psi. What a huge difference. The afm is not the original one so It is possible that it not set to factory and I tested the vacuum while blocking off other vacuum ports such as brake booster and heater controls and did not see any changes. Now this engine has only about 2 to 3 hours of run time on it after sitting since 1988. The inside of the valve cover was clean but is it possible that the rings may be a bit sticky and is there any way to tell or can anything be done about it?

Well I may need to redo my compression test I had the engine warmed up and all 6 plugs out but I did not hold the throttle open. I think I will test a few again with the throttle open.

I am not sure about the fit but I would think a quick few measurements will be able to tell. One other issue I have found with the old seats is that they stink. I found that the straw matting inside them can get moldy and put off a foul order I found this on two sets where I pulled out all the old carpet thinking it was that and still stank. Then I temporarily put one is a refinished car and found that it is the seats. If you have an old car and it reaks take that mat out and use some Silicone foam rubber sheet in it's place.

Well I got arround to cheching the vacuum and compression and was dissapointed with the results. The Vac was steady about 13" at 800 rpm and my compression was only around 135 to 140 on all 6. Naturally this is not what I was hoping for. This car aside from the Intake backfire runs pretty decent and it does not smoke at all. The plugs all had light gray deposits on them. So is there anything else besides bad or stuck that can cause this? Any thoughts on what my next move is here? I reallly want this car to be on the road this year.

I did some reserch on vacuum specs and I will do a comp and vac test Saturday and see how it turns out. I am leaning on low vac from a leak somewhere or the injectors not putting out enough fuel. The injectord I pulled off the other Z are a bit ragged on the outside and won't due for my restoration. If my next tests come out ok then I will get a new set of injectors. If this doesn't work I will need to look into the ECU or MAF.

I measured the fuel pressure by tying the gauge in just after the filter which is also new. That was with the vac line still attached to the FPR. I didn't check it with the line off. Where is the best port to test the Vaccum? Is there a way to test an ECU to see if it has drifted away from specs? I took a complete fuel rail with injectors off another 280z and connected it to my fuel line and cranked the engine to get the pump to run and got even lower pressure on that setup (25psi) and I did get some return from the return line but not quite as much. I checked the spray pattern on those injectors and got the same as the ones that are on the car. Basicaly a good strong steady stream but not really a spray. Does anybody know how much volume one should spray for lets say a minute at the 36 psi? I never checked the compression because this car only has 41,000 original miles on it although it was sitting for 25 years so I probably should check it anyway. This car is just about completely restored and I just can't get this bug out.

I didn't mention that the cap and rotor are new and I tried another ECU and both units the car ran exactly the same. It held 20 pis on the fuel pressure gauge over night. 32 psi is a little low and I wonder if that would cause it. Supposedly lean mixture would cause this intake backfire. So I am leaning towards slightly low pressure and maybe partially cloged injector screens. I have another 76 z that I pulled the fuel rain and injectors out of today so I can play with them and see how they spray compared to what the ones I used did. I read a post where someone pinched off the fuel return line to make sure the pump can pump more that the pressure needed.

I hope someone can help a little here. 1976 stock 280z backfire in intake when accelerating Not too bad but still it does it . I did all the FI tests timing is at reccomended 8 deg btdc at 800 rpm, checked for vac leaks, fuel press at constant 32 spikes briefly when reved to 40 and holds 30 for a while after shut off and return line puts out about 3 liters a minute while running. I do believe that it backfired more than usual while I had the return line running into the container. It has new wires and plugs. I did have the injectors and fuel rail out, while it was out I pressurized the rail untill the injector cleaner came out of the return line and I ran the injector cleaner through all of them them and they all seemed to work normally however they only shoot a steady stream with the cleaner and I don't know if it is a little thicker or is a stream normal. they did not produce a spray pattern but then again the cleaner used may be thicker than gas. They all put out about the same amount during a timed period. It may have backfired a little more than normal while I had the return line running into the container. when I had the injectors out I did not know there are filters in them so I did not check that or clean them. Does any body have any thoughts here?

What part of the wire broke I think they have studs coming out. I have taken mine apart and got them working. If you take the pump end off make sure you match mark everything so you know exactly how it goes back together. It may have junk in it and just need cleaning. I have one here that is intact but doesn't work too well.