I think my fuel pump is defective. :/

[KDMatt]

I'll check that out FastWoman.

At this point though, I'm starting to wonder if perhaps my FPR has something to do with this. If I fiddle with the vacuum hose attached to it (i.e. clamp it) the pressure goes up.

Right now, at idle, I'm sitting at about 30 PSI, but if I clamp it, I can take it up to 33/34, which is leading me to believe that the flow may not be as bad as you suspect.

I've been considering getting a solid aluminum fuel rail and adjustable FPR, perhaps now is the time.

[FastWoman]

KD, vacuum to the FPR will drop the fuel pressure. That's what it's supposed to do. However, if you can't get a static pressure higher than 37, your pump is marginal at best.

FAIW, the OEM FPR is VERY GOOD at regulating fuel pressure quickly and precisely. I did try out a cheapo chinese Aeromotive FPR knockoff, and it regulated pressure very sloppily. I returned it for a refund. I have no idea how tightly a real Aeromotive FPR regulates, but I doubt it could do much better than the OEM.

[darom]

KDMatt, here is my original post re: the lean condition:

http://www.classiczcars.com/forums/showthread.php?41973-TPS-smog-and-high-CO-discussion

[KDMatt]

@darom, Thanks for the link, I'll check it out.

@FastWoman, My FPR is a replacement aftermarket one, made by "Niehoff" ... from Kragen/Checker/CSK a number of years ago.

If you want the long story, last fall I was getting a lean condition, and low pressure. Since I'd replaced the FPR a number of years prior, I assumed that my aging, untouched pump and tank had something to do with the problem. The tank, I knew, was full of crud, so dropped it, and figured I ought to replace the pump at the same time. That's why we are where we are now.

I've tested the EFI pretty extensively, and all of the electricals check out too.

The low idle pressure still remains, and this is leaving me fewer and fewer components to be suspicious of. However, I will try your test, and see what the return flow looks like with the engine running.

[KDMatt]

Hey, Fastwoman

I checked out the fuel return today (would have done it sooner, but I had a film competition to participate in over the weekend), and it looked pretty healthy both with the engine off, and with it running.

I opened the throttle a bit too, and the return flow grew stronger when I did this.

What are we thinkin' ... FPR?

[KDMatt]

Alright, I'm losing my mind over this now.

Through the generosity of another local Z-owner, I acquired a later, ZX-styled fuel rail with FPR that were both tested and working good. I installed it on my car, and the fuel pressure was right where it ought to be.

I took it out for a spin, and it's bucking/backfiring/sputtering/struggling to climb hills...

This is the exact same behavior I was getting before I replaced anything!

It was this very behavior that led me to believe my pump was bad, that led me to believe my tank was clogged, that led me to believe my FPR had gone kapooey.

All of these components have been changed, in addition, I've done the battery of tests recommended in the FSM, and everything checks out.

I'm really at a freaking loss here guys.

The only thing I feel like I haven't tested or even considered is the ECU itself. What are the odds of that thing going out?

I don't want to have to gut the EFI and go Megasquirt or something if I don't have to... but if there's no other alternative.

[Zed Head]

How much have you actually driven the car since Post #1? How much driving after all of the changes, but before the ZX fuel rail?

I read through the thread and it looks like all of the work has been in the garage. It may be that you've been focusing on the wrong thing, or that you had two problems and now you just have one.

[KDMatt]

Zed, thanks for responding.

This was her first time out of the garage since I parked in November.

I was having the same running lean/bucking/backfiring issue in the fall. When I pulled her out about 4 or 5 weeks ago, I ran through gamut of tests listed in the FSM, thinking that my fuel injection electronics were at fault (It feels like the pulses are too short or something), when all of the results came back within spec, I turned my attention to the physical/mechanical aspects of the EFI, which led me to drop the tank and get it flushed, and replace the pump (and now, the rail/FPR as well).

The last time I checked the vacuum, that hadn't changed (and I've faced vacuum leaks before, this isn't behaving like a car with low vacuum).

I'm really just at a loss, and I would like to be able to drive the damn thing.

The only other component I can maybe think of is the Auxiliary Air Valve/Air Regulator etc.

I had a thought the other night that if it were to get sticky and not close all the way, this stood the chance of throwing off my fuel mixture. Otherwise... is there a testing procedure for the ECU itself?

[FastWoman]

Alright, I'm losing my mind over this now....

I'm really at a freaking loss here guys.

The only thing I feel like I haven't tested or even considered is the ECU itself. What are the odds of that thing going out?

I don't want to have to gut the EFI and go Megasquirt or something if I don't have to... but if there's no other alternative.

Been there, done that. Look for my "purs like a kitten" thread, and dig through it. It seems as though some of these old ECUs drift in their calibrations, delivering shorter pulses to the injectors than they should. You can "fool" them back into proper calibration by adding resistance to the coolant temp sensor circuit.

But before you go altering the CTS circuit, make certain your fuel pressure is right. You say you're getting lots of return (healthy pump), and your running pressure is probably about right (30); however, you should pull the vacuum line from the FPR and verify that the pressure increases to 36.3 psi. Also plug the return line and verify that the pressure rises to approx 45 psi or higher (further testing your pump). Then I think you'll have the rest of the story on your pump/FPR situation.

Also, to rule out the possibility of any pesky vacuum leaks, perform my "yogurt cup test." If you have any leak anywhere, you'll know it.

Edited June 18, 2011 by FastWoman

[Zed Head]

Your symptoms pop up occasionally and there are varying opinions on how to confirm the solution before replacing parts. It's a dilemma. In my own personal case, my engine had the same sort of symptoms as yours and I too tested everything and ended up replacing the AFM, which showed as out-of-spec. The rebuilt AFM was the solution for me, but not quite so for others, see here

(http://www.classiczcars.com/forums/showthread.php?40392-76-280Z-Question-on-dist-manifold-vacuum-dist-timing-fuel-pressure-brake-booster&highlight=jennys280z)

Cozye and FW have had success with modifying the water temperature circuit, but their problems were minor compared to what I think you're describing. When my AFM was bad, the car was barely drivable, and very embarrassing to be in on the road.

The AFMs for 1975 - 1978 are essentially the same except for the fuel pump cutoff switch, which 1978 does not use. If you could borrow one, you might be able to get a cheap diagnosis, beyond measuring resistance on the AFM circuits.

[KDMatt]

Thanks for the quick responses guys.

@FastWoman: Now that I have the later, ZX-styled rail, removing the vacuum line will be a cinch, so I'll try that out. I'll also try plugging the return to see what's up.

Also, I saw you mention your 'yogurt cup' test in another thread, and I've been trying to find your video/instructions for it, but I'm not having any luck. Can you help me out with that?

Also, interesting bit about the ECU. My car used to run somewhat rich until, one day in September, it just didn't... Unusual for it to go so wonky so quickly? ... or does that seem common enough?

@Zed: My first inclination was the AFM. I've got a spare in my garage that I swapped in when this first set on, and this didn't change anything. Is there a guide somewhere for checking to see if it's "within spec?" I've been combing over my FSM and haven't seen mention of this.

Thanks!

[FastWoman]

KD, something suddenly going wonky does sound most likely like something electrical. Yes, it's very common for something to go out suddenly -- to break, as it were. So it might not be a long-term drift problem like Cozye and I experienced with our ECUs.

I think I described the yogurt cup test in that long "purs like a kitten" thread. It's simple, though: Simply remove the AFM, and stuff something like a yogurt cup (Yotastic brand worked for me) in the AFM-to-throttle body boot to block off all air flow. Pull the brake booster vacuum line loose, and hook a clean hose (that you don't mind putting your mouth on) to the intake manifold at that fitting. Then pressurize the entire intake system (including crank case, valve cover, and probably a couple of cylinders with open intake valves) by blowing hard into the tube. You might have to hold the cup to keep it from popping out of the boot like a cork. By doing this, you'll be able to feel how fast air leaks out of the entire intake system.

Now pull off the tiny vacuum line next to the brake booster line, which runs along the firewall to the opposite fender and feeds the HVAC system. With that fitting open, try inflating the intake system again, and note how fast the air leaks back out. The second time, you are introducing a known leak that is small enough to be of only minor consequence to the fuel/air ratio. If your system is tight, you will notice a substantial difference in air leakage rate between your two tests. Also most of the air you blow into the intake on the second test will shoot right back out of the smaller HVAC fitting. If your intake is not tight, the air will probably leak out quickly either way.

If the total of your leakage in the first test is substantially less than the leakage through the HVAC fitting in your second test, then you don't have any vacuum leaks large enough to worry about.