I think my fuel pump is defective. :/

[KDMatt]

Alrighty, so I followed through with the general battery of mechanical fuel tests you recommended.

At idle, when I pulled the FPR's vacuum line, I got it to stay at 36.3 PSI, even while I revved it.

When I blocked off the return, I got the pressure to spike at around 70 psi with the engine running.

I think it's safe to say my FPR and fuel pump are both doing their jobs, eh?

Regrettably, I haven't done the yogurt cup test yet, but I will get to it if you still feel it's relevant.

I had a fellow Z owner over this evening to help me sort through some of this crap, and he was pretty adamant in the possibility of it being ignition related, even though I'm not so sure I'm convinced yet. (He wants to investigate the ignition module under the passenger side dash).

We also measured the resistance of the water temp sensor and compared it to the resistance chart in the FSM. It looks like it might be slightly out of whack? At 122 degrees, the FSM says the resistance out to be between .74 and .94 kiloohms ... or rather 740 and 940 ohms. We measured the resistance with the temp at about 124 degrees, and my multimeter only gave me about 650 ohms.

This doesn't take into account the fact that the resistance was at the thermostat, and we were measuring temperature at the radiator, which would be cooling off faster.

Still ... it could be off by anywhere from 100 to 300 ohms of resistance. Is this significant enough to cause a difference?

EDIT: Oh, and here's the particularly odd thing.

My RPM stumbles/misses a bit in its lower range, but once I get past 3000 to 3500 RPM, it smooths out and pulls hard. :/

Edited June 21, 2011 by KDMatt

[FastWoman]

Well, a low CTS resistance is going to result in a bit leaner running; however, I don't know whether that small error is going to have that large an effect (stumbling, bucking, backfiring -- through intake, I presume).

If the problem occurred suddenly, I'd probably still look for an electrical contact or part that's bad. Do the full round of electrical tests in the EF section of the FSM. It doesn't take all that long. If you don't find anything there, then you should probably just go on a hunt to look for anything out of whack. Sorry, but there's a lot of stuff:

HERE'S A ROADMAP FOR YOU, in no particular order. Others may have some additional ideas:

Yes, do the yogurt cup test to make certain your system is tight. It's very quick and easy, and the results are unambiguous.

Then while the AFM is out of the car (for the yogurt cup test), open it up, and check the tension of the clock spring, using the method outlined on the Atlantic Z website -- tech tips -- beer can and water method. Clean all the contacts, and do the electrical tests in the FSM. Reinstall, but don't seal back up the access cover yet.

Pull your distributor cap to see whether the breaker plate is stuck or whether it rotates freely. Those go bad and jam up. Then check your timing to see if it's within specs.

Read your plugs. Better still, show us pictures. One list member had a goofy problem where his EGR leaked and fouled out his #4-#6 cylinders, so that he was running on only 3 cylinders. Ya' never know what you'll find, but we definitely knew something was up when he showed us his plugs. (Note: I couldn't talk him into doing the yogurt cup test. He would have retained much more hair on his head if he had done it in the first place! )

Put your multimeter on your plug wires to make sure they test good. (See the FSM for resistance per meter.) Also run your engine at night in the dark to see if there are any stray sparks. This would be a good time, in general, to replace any old ignition components -- cap, rotor, plugs, wires. Use NGK spiral wound blue wires and NGK plugs -- probably B6ES-11 on yours, but check your manual.

Pull your valve cover and adjust your valve lash. Put your transmission in 5th gear, and push it to rotate the engine to TDC. Check the alignment marks on the cam sprocket. You'll be looking for wear in the chain that would cause your valves to be late in their timing. (Note: This is not a "suddenly bad" sort of thing, but it should be checked.)

Check your compression.

Now if your compression is good, valves are right, timing is right, ignition is good, fuel components are good, FUEL PUMP AND FPR ARE GOOD (WOOHOO! ), AFM is to spec, and there is no EFI component you can find that is failing, it's probably the ECU that's gone wonky.

ECUs can go suddenly bad via a fractured solder joint. ZTrain had this happen, and he fixed it by opening it up and re-flowing all the solder connections.

They can also just drift out of spec over time, as their semiconductors get tired (see above). This happened to Cozye and me. In both our cases, the ECU drifted towards shorter and shorter pulse widths, and we corrected by adding resistance to the coolant temp sensor circuit.

To check whether you're running rich or lean, you can tweak the vane of the AFM with the engine running, to open it up or close it off a bit. My guess is that your engine will pick up rpms when you open the vane a bit, indicating that it's running lean.

Anyway, it's a lot of stuff to check through, but if you're methodical about it, you'll come out the other end with a nicely running engine, probably after finding at least a half dozen little problems that added up to a bigger problem.

Edited June 22, 2011 by FastWoman

[KDMatt]

Hey Fastwoman, since my pump is no longer in question, I'm going to start a new thread. Got some new stuff to report.