russ in va Posted December 13, 2007 Share Posted December 13, 2007 My '70 240 is powered by a stock l28et (83 style). It was running lean throughout the rev range on the dyno, so I checked the fuel pressure. Testing results before changing any parts: - Key on pump running engine off = 35 psi (should be 38-40) - At idle = 27 psi (s/b 30-32) - Throttle tip in = 33/34 psi (s/b 37) - At 7psi boost = 40 psi (s/b 47) - At idle with return line clamped off = 44 psi initially, dropping to 42ish (s/b ??? 60 ???) Installed new autozone pump: - all test results the same EXCEPT with return line clamped it now holds 75psi Installed new autozone stock replacemet FPR: - no changes at all Any ideas why all my results are coming back 3 to 7 psi below spec? Note: All these results were using a homedepot psi gauge. I subbed in a Snap On gauge I borrowed from a friend and the readings were about 1 psi higher, but still below spec. I am using the stock fuel supply and return hard lines. Barring any other solution, I'm planning to by an MSD adjustable boost referenced FPR (not a rising rate FPR or FMU if you will) just to try to get the car to work as designed. I can get an MSD part # 2222 for $72 at Autozone. Thoughts will be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
naviathan Posted December 13, 2007 Share Posted December 13, 2007 If I remember correctly isn't the fuel supply line on the 240 smaller than the one in the 280 which could cause your problem? Although I don't think your readings are far enough off to cause any issues. It could be your AFM needs adjustment. Quote Link to comment Share on other sites More sharing options...
Clifton Posted December 13, 2007 Share Posted December 13, 2007 It's not the 240 supply line. I've run alot of power with mine. If the pump can supply pressure in excess of what the regulator is set at it has to be the regulator. I'm surprised it has a shutoff at at only 44 psi, especially for a turbo, kinda low. I would have atleast bought a small Walbro. Quote Link to comment Share on other sites More sharing options...
Thumper Posted December 13, 2007 Share Posted December 13, 2007 Also most fuel pressure guages are in accurate. As long as you get a 7-8psi difference between vaccum and no vacuum then your fpr is working correctly. So I would look into other things that is causing you to run lean. You did get a new TURBO fuel pump correct? Turbos flow more than regular. Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 14, 2007 Share Posted December 14, 2007 Also most fuel pressure guages are in accurate. As long as you get a 7-8psi difference between vaccum and no vacuum then your fpr is working correctly. So I would look into other things that is causing you to run lean. You did get a new TURBO fuel pump correct? Turbos flow more than regular. That's right - the pressure that you see at idle really depends on how much vacuum you have at the time. The FPR simply maintains a constant pressure difference between the fuel pressure and the absolute pressure in the intake manifold. So, for instance, 18 in of vacuum equates to about 9 psi below the ambient pressure (the manifold pressure you see when the engine is off). So in this case if you are seeing 35psi with the engine off, you should expect to see 35-9 = 26psi with at idle. Also, fuel flow varies with the square root of pressure, so the actual difference you should expect to see between 35psi at the rail and 38 is about 4%. So if you would normally see 12 AFR at 38psi, you should expect to see more like 12.5 AFR at 35psi. Quote Link to comment Share on other sites More sharing options...
savageskaterkid Posted December 14, 2007 Share Posted December 14, 2007 I don't know too much about the 240 lines, but I know they are smaller. I also don't know about the 2222 msd, but I had a 2225 MSD and it worked great, it would pump 100psi all day long. Can be had for 100 online. Might be able to get it at autozone. Quote Link to comment Share on other sites More sharing options...
russ in va Posted December 14, 2007 Author Share Posted December 14, 2007 Thanks for all the info. It is the pump they specified for the turbo ... but they specify the same pump for the n/a motor (and for EVERY other Nissan made that year). It's a generic thing. But I don't believe the flow rate of my pump is my problem. We are talking about fuel pressure being too low at idle as well as everywhere else. When the car is under load I don't have a problem with pressure falling off (which is what it would do if the pump was not keeping up), it's just too low all the time. The AFM may well be out of adjustment, but before I mess with it I wanted to get my fuel pressures right (as per the FSM). I'm going to try the adjustable FPR and see what that does, then I'll try messing with the AFM if need be. If Tim's numbers work out though, and 3psi makes a half point change in my AFR, then I may just turn the pressure up a scosh beyond the factory spec and get everything where I want it that way. I've got a boost controller ready to go in place and bump the boost up to 10psi as soon as I get this sorted out so I'm getting kind of impatient! Quote Link to comment Share on other sites More sharing options...
russ in va Posted December 14, 2007 Author Share Posted December 14, 2007 BTW, the MSD 2222 is the adjustable FPR that I am planning to buy. The MSD 2225 is a fuel pump. If I were'nt so impatient, I would have gotten an aftermarket pump (MSD or Walbro), but again I don't think my new generic pump is the problem since it will make 75 psi with the return line clamped off. I just want to get the pressures to meet the stock settings to get my AFR's in line so I can turn up the boost! Quote Link to comment Share on other sites More sharing options...
savageskaterkid Posted December 14, 2007 Share Posted December 14, 2007 got it, let me know whats going on, as I have a few stock 280zx fpr's lying around, nothing special, but they worked, and your not too far away and atleast one of them worked well on my Z. Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 14, 2007 Share Posted December 14, 2007 The AFM may well be out of adjustment, but before I mess with it I wanted to get my fuel pressures right (as per the FSM). I'm going to try the adjustable FPR and see what that does, then I'll try messing with the AFM if need be. If Tim's numbers work out though, and 3psi makes a half point change in my AFR, then I may just turn the pressure up a scosh beyond the factory spec and get everything where I want it that way. I've got a boost controller ready to go in place and bump the boost up to 10psi as soon as I get this sorted out so I'm getting kind of impatient! Did you ever say how far lean you are? I thought that the stock FPR was supposed to be 2.5 bar, or 36.25psi, so the difference between that and 35psi would only equate to a difference from 12 to 12.2 afr. Just want to make sure it's clear that the fuel pressure might not not be main contributor to your problem. For instance, if you are using stock injectors, they might just be gunked up and not flowing to spec. This would be a much more important problem to focus on, since this will most likely result in afr differences from cylinder to cylinder. If you "fixed" this problem by upping the fuel pressure, you could run into a situation where one or more cylinders are still lean, even though your wideband readings look okay. Quote Link to comment Share on other sites More sharing options...
russ in va Posted December 14, 2007 Author Share Posted December 14, 2007 Tim, that's a good point. My AFR is tracking in the 13 to 13.5 to 1 range from 2k rpms to 4500, then it creeps up steadily crossing 14:1 just under 5000 rpms and touches 14.5:1 at 5500 where I let off fearing potential damage. Max power on the dynojet is 162rwhp at 5k, with max torque of 188 ft-lbs occuring at 4300. The plugs all look good and the same, but I don't know if you would be able to tell by a plug inspection that an injector was a little off. BTW, these numbers are with a 2.5" mandrel bent exhaust and straight through core 2.5" magnaflow muffler. With an open downpipe (2.5 mandrel as well) and no other changes it made 174 hp and 196 lbs-ft (I have to admit that outdoor ambient temp was about 20 cooler on that run, though the temp in the shop according to the dynojet's thermo was only a couple of degrees lower. Of course these are all SAE corrected numbers anyhow so hypothetically it should not matter ... but it is forced induction.) I used to call BS on the notion that it was important to have 3" exhaust. Now I'm a believer, too bad I already spent the money on the 2.5" cause it's going to have to stay a while 'till I'm ready to spend the money to redo it. Quote Link to comment Share on other sites More sharing options...
evildky Posted December 17, 2007 Share Posted December 17, 2007 another vote for the adjustoable bosch unit, and keep in mind the base fuel pressure at idle (thinking it was supposed to be 37 psi?) is supposed to be measured with the vac line off and plugged Quote Link to comment Share on other sites More sharing options...
russ in va Posted December 17, 2007 Author Share Posted December 17, 2007 I installed the adjustable FPR (not RR, just adjustable). I now have 30 psi at idle (with the vac line hooked up), 40 psi with it unplugged (same as key on, engine off, pump running), 50-51 at full boost (with boost controller set to make 10lbs of boost). But, I just sold/traded the car to a friend of mine and his plan is to pull the turbo/injection off and put S/U's on it! It will sound much better (which is why he's doing it) but I'm loving the 200 lbs-ft of torque it makes now, he's going to lose ... what about 70 of that? Hmph. So I need to do some searching for him, but can anyone tell me off the top of their head, does my turbo motor make less compression than an N/A because it has dished pistons, larger combustion chambers or both? He has an old E88 (late 240) head with a set of 280Z valves to bolt on, but I'm not sure that's going to get his compression back up to "normal". Not really my problem but I'd like to help him in his quest if I can. (He really wants a set of ITB's he can run with MegaSquirt, but that's a whole different search he needs to do.) Quote Link to comment Share on other sites More sharing options...
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