NamorNhoj Posted August 16, 2013 Share Posted August 16, 2013 Hey all -So here's my problem with my 1976 fuel-injected 280z (in all it's layers). My car has been suffering from a rough start-up lately, where the car has trouble turning-over, until it eventually fires with just enough power to get the motor running. A few blips of the throttle helps the car find a steady enough idle that it runs smooth enough to drive. And until the car is warm, the car comes close to dying when not under load (again, I tease the throttle a little to keep the car alive).Then, it all seems to even out -- for a while. Then, a few miles into my drive (or after running strong for about 15min or so), the car will bog when I go to touch the throttle. The car will idle, but as soon as I go to give it gas, there will be no response whatsoever - almost as if the car has shut off, but it hasn't. Sometimes, if I turn the car off / on right away as I notice the problem coming on, I can get power back out of the motor enough to pull over and wait it out.Turning the car on / off a couple of times usually gives me enough second chances to where I can limp the car home. But WHAT THE **** IS GOING ON?If it's worth mentioning, I've only done so much as intake / exhaust on my car. I upgraded my coil, thinking this was the culprit, but the problem hasn't changed at all. Also had my tank refreshed / fusable links upgraded. I've changed my fuel filter, and replaced my plugs. My timing is correct (except for when it misfires when this particular problem arises), and my battery / alternator are up to snuff.What could this be?My next suspect in trying to track down the issue was going to be my fuel pump - is what I've described symptomatic of a failing fuel pump??Any amount of help would be a big help.Thanks in advance. Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 16, 2013 Share Posted August 16, 2013 Measure the fuel pressure, before you change the pump. What does this mean "If it's worth mentioning, I've only done so much as intake / exhaust on my car. "? Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 16, 2013 Author Share Posted August 16, 2013 Measure the fuel pressure, before you change the pump. What does this mean "If it's worth mentioning, I've only done so much as intake / exhaust on my car. "? Just letting people know to what extent the stock engine has been "modified" -- really not at all. Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 16, 2013 Share Posted August 16, 2013 If you've taken the manifolds off, you might have left a hose or two disconnected, or have a messed up injector seal. All air must pass through the AFM (except for the tiny amount that comes through the carbon canister). Check for vacuum leaks. A leak would give you a lean mixture, which would work better for a warm engine. Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 16, 2013 Author Share Posted August 16, 2013 If you've taken the manifolds off, you might have left a hose or two disconnected, or have a messed up injector seal. All air must pass through the AFM (except for the tiny amount that comes through the carbon canister). Check for vacuum leaks. A leak would give you a lean mixture, which would work better for a warm engine. I've done a pretty extensive vacuum leak check - sprayed carb cleaner on everything, listening for any sort of idle change, and there was none. Also, I don't know if a minor vacuum seal would cause for such abrupt losses of throttle - the car bogs with no response sporadically without warning. Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 16, 2013 Share Posted August 16, 2013 Back to fuel pressure then. I've had a pump that worked fine when cold, crapped out after running for a little while. The motor was dying. Roll the dice again or take a measurement. Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 16, 2013 Author Share Posted August 16, 2013 Back to fuel pressure then. I've had a pump that worked fine when cold, crapped out after running for a little while. The motor was dying. Roll the dice again or take a measurement. Much appreciated. I understand the MSD 2225 unit is a good pump for the money, and if it's just $100 or so, I may just have to try it out -- a lot of swinging and missing in diagnosing this thing, tho. Who knows... Quote Link to comment Share on other sites More sharing options...
xonix_digital Posted August 19, 2013 Share Posted August 19, 2013 I had these issues and it turned out to be fuel pressure related. Actually it was lack of flow due to my fuel filter being due for replacement. Quick and easy test is to replace that. That and fuel pressure gauge will be helpful in diagnosing this one. Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 19, 2013 Author Share Posted August 19, 2013 I had these issues and it turned out to be fuel pressure related. Actually it was lack of flow due to my fuel filter being due for replacement. Quick and easy test is to replace that. That and fuel pressure gauge will be helpful in diagnosing this one. Replaced my fuel filter about 200mi ago. Need to get a fuel pressure gauge on it to really test what's up. Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 19, 2013 Author Share Posted August 19, 2013 UPDATE: Decided to drive up to Yonkers from Brooklyn yesterday (followed closely by a friend in the event of something happening) and much to my surprise, the car made the entire trip without issue. That's 20 miles on the highway, through all gears, without any bogging whatsoever. Even at the toll plaza halfway through the trip, idling went without incident. Once in Yonkers, I drove the car around all weekend: maybe 30 miles, give or take. Again, no issues. Then, on my return trip this evening, upon reaching the toll plaza halfway into my trip, idling for the toll became an issue. I bogged at idle, and when I feathered the throttle to get some life back into the car, the response was flat. I turned the car off / on, and upon restarting, I was able to rev the car back into some life in order to make it through the toll. Then, for the rest of my trip, the car ran strong through all the gears. ALSO WORTH NOTING: when the car was bogging at the toll plaza, I noticed a significant drop in oil pressure. What might this be symptomatic of? Also - even though the car wasn't bogging like it had been this weekend, the car does have a bit of a sputter when trying to get rolling in first gear. (?) Any input?? Thanks! Quote Link to comment Share on other sites More sharing options...
DatsunZman04 Posted August 19, 2013 Share Posted August 19, 2013 I say its a fuel issue somewhere. What do your plugs look like after it does the hesitation, are they fouled?? Or they white? Vaccum leaks, bad fuel or fuel pump would be where I would start. Can you hear the pump kick on when your keys are on acc? to let it build up pressure before you start it? A 25$ fuel pressure gauge would tell you a lot, get a fluid filled one it will be more accurate. Just tips where I would start, I hope that helps. Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 19, 2013 Author Share Posted August 19, 2013 I say its a fuel issue somewhere. What do your plugs look like after it does the hesitation, are they fouled?? Or they white? Vaccum leaks, bad fuel or fuel pump would be where I would start. Can you hear the pump kick on when your keys are on acc? to let it build up pressure before you start it? A 25$ fuel pressure gauge would tell you a lot, get a fluid filled one it will be more accurate. Just tips where I would start, I hope that helps. Plugs are clean. No vacuum leaks. Picking up a fuel pressure gauge today. Quote Link to comment Share on other sites More sharing options...
xonix_digital Posted August 21, 2013 Share Posted August 21, 2013 Since the problem is intermittent I would get one that you can install in the cabin. If its under the hood you wont be able to see it when the issue occurs randomly. Probably obvious but just mentioning it from a diagnostic perspective. Quote Link to comment Share on other sites More sharing options...
NamorNhoj Posted August 23, 2013 Author Share Posted August 23, 2013 Since the problem is intermittent I would get one that you can install in the cabin. If its under the hood you wont be able to see it when the issue occurs randomly. Probably obvious but just mentioning it from a diagnostic perspective. When the car bogs, it will bog until the car is turned off / restarted. UPDATE: Installed a fuel pressure gauge after my (relatively) new fuel filter today under the hood. Drove around without incident for a little while, and when the car started showing signs of bogging, I popped the hood to monitor the gauge. Even as the car bogs (power cuts off sharply), the fuel pressure gauge reads a steady 28psi -- obviously low because the car won't rev past the bogging / loss of throttle. When the car is running correctly, it idles around 28-30psi, and when revved, the pressure jumps to around 40psi (which I understand to be correct pressure readings for the 280z). So now what!? Quote Link to comment Share on other sites More sharing options...
IncompetentOne Posted September 3, 2013 Share Posted September 3, 2013 Has your tank ever been cleaned? could be bad gas causing rough running. Also, i know that you sprayed car cleaner over the vac lines and whatnot but just check the pcv hose at the bottom of the intake for good measure. When you turn the car on from a cold start, the Idle air valve should help keep it from bogging or trying to cut off... but if you removed it like I did you will have to wait until the car warms up in roughly a minute. good luck with the Z! Quote Link to comment Share on other sites More sharing options...
cgsheen Posted September 6, 2013 Share Posted September 6, 2013 (edited) When the car bogs, it will bog until the car is turned off / restarted. UPDATE: ... When the car is running correctly, it idles around 28-30psi, and when revved, the pressure jumps to around 40psi (which I understand to be correct pressure readings for the 280z). So now what!? Sounds electrical to me. Have you checked and cleaned all of your electrical connectors on the EFI harness? You may want to grab the FSM and go through the EFI components testing. It's not hard, simple tools and an inexpensive multimeter is all you need. 28-30 should be about right for idle fuel pressure. 40 is probably a little high unless you've got 4 pounds of boost. Should run about 36.3 PSI MINUS whatever the vacuum on the intake manifold is at the time. Edited September 6, 2013 by cgsheen Quote Link to comment Share on other sites More sharing options...
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