78 280z idle problem

[Zed Head]

One trick I've used to verify maximum travel of the master cylinder piston is to adjust the rod so that the clevis pin slides in to the pedal bushing with no effort.  If you have to pull the pedal down or push the rod in or pull the rod out to get the clevis pin in then it's not right.  While you're there you can eyeball the pin and the hole for wear.

I've also used a thread to pull the clevis pin up to the hole so that I can finagle it in the rest of the way with a screwdriver.  I can't get my hands up there.

[Jack Pearcy]

3 hours ago, EuroDat said:

I thought the master cylinder was replaced earlier before the clutch and pressure plate was replaced. Now reading post #39 I agree.

My internet connection is not the quickest working out of a landcruiser or campsite and I scrolled past it.

Chaseincats has a good point. It looks like an incorrect master cylinder push-rod or adjustment. If it has the correct push-rod it should be adjusted according to fsm. See attachment.

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Oh that's awesome! Thanks so much for that I'll be sure to try it out and let you all know how it goes! Now on the original topic of this thread I've been running some more tests now that the trans is back in and today I pulled the return line off the fuel rail and ran the car with the fuel pump on and plenty of fuel was coming out of the return line but the car was still smoking and running really rich like it had before. I turned the pump off and sure enough fuel stopped coming out of the rail but the idle cleared right up and it started running great which I still wish I could explain. Since I've replaced the AFM, fuel injectors, fuel pressure regulator, and tried tuning the air-fuel mixture with the screw on the back of the AFM, and ruled out the possibility of a return line clog, how else can I adjust the air-fuel mixture to make it run right? Could this be a problem with my ECM? I didn't think that controlled the ratio but I could be wrong. Thanks to everyone who has replied to my posts you're all awesome I love this community!

[Zed Head]

18 minutes ago, Jack Pearcy said:

 Since I've replaced the AFM, fuel injectors, fuel pressure regulator, and tried tuning the air-fuel mixture with the screw on the back of the AFM, and ruled out the possibility of a return line clog, how else can I adjust the air-fuel mixture to make it run right? Could this be a problem with my ECM? I didn't think that controlled the ratio but I could be wrong. 

Doesn't look you've run the tests described in the FSM or the Fuel Injection book.  You need to do those tests, at the ECU connection.  Even new parts can be bad.  It's the first thing mentioned in hundreds of threads, so many times that we often forget to say it again.  Get a meter and do the tests.

The ECU could be bad also, but without testing the other parts, it's an expensive guess.

[chaseincats]

I still don't understand how the car is running w/o the fuel pump going

[EuroDat]

Ther could be a couple of things causing it to run while the pump has stop. Idling is essentially a no load situation and requires minimal fuel.

It looks like (not confirmdd yet) that you have a chronic over fueling issue. You might even have fuel laying around in the inlet manifold. Stop the pump and the air/fuel ratio starts leaning out and it briefly runs better. Well, it's a theory...

You NEED to buy a fuel gauge and mount it in the line after the fuel filter. Don't assume stuff. You need to test and confirm or dismiss possabilities. Not doing that will set people on the wrong train of thought and you will be chasing you tale for weeks. Been there, done that, so to speak.

The people here can and will help you a lot, but you need to give them solid informatie.

Tests you should do asap.

- Fuel pressure: If it is a leaking injector or Cold Start Vavle, you can confirm that with the gauge. Ill try and upload a simple procedure I use for testing. Need to find it on my tablet...

- Check the spark plugs. That are probably black and sootty from overfuelling. Remove them and stick them through a piece of cardboard with the cylinder number written next to it. Make a photo and post it here. See attachment sootty plugs from a badly leaking cold start valve CSV.

- Compression test. Do a compression test and confirm all cylinders are in goed order. It's not that important what the reading is, unless you are reading 75psi on all cylinders.... Most compression gauges are not calibrated accurately showing pressure so 140 could be 160. What you are looking for is variance between the cylinders. They should be (for example) all 135-145psi. Bad would be something like 4 cylinders reading 145psi and two reading 95psi and 110psi.

- Read and start doing the tests in the fuel injection bible. There is a very good reason why we call it the bible. 

 

Instruction - Fuel Pressure Test 280Z RevB.pdf

Edited June 28, 2019 by EuroDat
found my write up on the tablet. :)

[Dave WM]

finally got around to testing how long an engine will run with the fuel pump off. My setup on the test stand (which has much more rubber hose, no hard line but for the fuel rail) will run for about 13 seconds. You can tell its off after about 2 seconds, then itl struggle for the last 11 or so second till it dies. This was at idle of course.

I like the theory of a pooling of fuel in the manifold for any kind of run on longer than that. Still have doubts about 8-10 minutes (think that was what was said). Kind of pointless to keep talking about it, you have to get the fuel pressure gauge and start going thru the process. I only brought it up since I had said I would check the time a engine would run with the pump off, on my setup.

Edited June 28, 2019 by Dave WM

[Jack Pearcy]

6 minutes ago, Dave WM said:

finally got around to testing how long an engine will run with the fuel pump off. My setup on the test stand (which has much more rubber hose, no hard line but for the fuel rail) will run for about 13 seconds. You can tell its off after about 2 seconds, then itl struggle for the last 11 or so second till it dies. This was at idle of course.

I like the theory of a pooling of fuel in the manifold for any kind of run on longer than that. Still have doubts about 8-10 minutes (think that was what was said). Kind of pointless to keep talking about it, you have to get the fuel pressure gauge and start going thru the process. I only brought it up since I had said I would check the time a engine would run with the pump off, on my setup.

I’ve been messing around with the car and it’s stopped doing that, couldn’t tell you why, but I’ve discovered a few things: one is that my newish plugs are filthy black and two that my CSV is broken but in addition to that the engine runs amazing with the CSV removed and the hole it went into left open, although it idles at 2,500 when I do that. It also starts to die if I open the throttle at all. I’m going to run a compression test next but hopefully this info can help lead to a solution.

[Jack Pearcy]

At this point I’m pretty certain it’s not a pressure issue, it’s just that the injectors are giving it a crazy amount of fuel and it’s not something that can be tuned away anywhere else but through editing the amount of fuel the injectors are putting into the engine if at all possible. Eurodat thank you so much for the fuel pressure test instructions, I will continue to review them and hopefully find a way to do what I have described!

[siteunseen]

can't you just unhook the fuel hose or the 12v clip on to CSV?  I guess the 12v clip would be easiest.

[Jack Pearcy]

6 minutes ago, siteunseen said:

can't you just unhook the fuel hose or the 12v clip on to CSV?  I guess the 12v clip would be easiest.

If I unhook the 12v clip it just idles at 300 and dies like it’s been doing, if I detach the fuel line it will spray fuel and I will lose pressure to the rail. I think the big takeaway here is that it’s the vacuum create by removing the CSV that allows the engine to idle where it wants with the amount of fuel it’s getting. Since it’s idling at 2500 it’s getting as much fuel as it would need to run at 2500 but at idle so the air fuel mixture is off and it dies. If I close this vacuum and try and open the throttle enough to allow this much air in the AFM picks up that’s more air is entering and dumps even more fuel in, throwing off the mixture again. I wonder if there’s a way to adjust the AFM to put less fuel in aside from opening the bypass screw since that doesn’t allow enough air in to solve the problem. Maybe removing the cover and adjusting the prong? Probably a bad idea but I’m interested to hear what you all think

[EuroDat]

You could have a couple of issues that cauld cause an overfueling problem.

Most common are leaking injectors, leaking CSV or a bad temperature sensor or wiring going to the temperature sensor. The more resistance the colder the ECU thinks the engine is and compensates with more fuel. 

You seem to be getting a lot more fuel than a faulty temperature sensor would allow, but doing the checks will confirm or dismiss it. When you check it, do the check at the sensor (sensor to ground resitance) and than again at the ECU connector (Connector pin 13 to ground resistance) They should be the same. Refer to the bible for the correct resistance for temperature range.

Note: Use the 1980 Bible. It is for all models 280Z, 280ZX en 810 Maximas up to 1980.

The other book is for the 1974 to mid 1976 models.

Edited June 28, 2019 by EuroDat

[Dave WM]

don't mess with the AFM, while its tempting, its like NOT to be the issue, unless someone had beat you to it and messed with it.

Follow EuroDat instructions and report back the findings on the Temp sensor resistance. Also note the temp of the engine, as it needs to match up with the resistance reading table.

too much fuel resulting in rich mixture is generally from:

CTS (too high a resistance for the temp of the engine)

CSV (stuck on)

leaking FPR (fuel from the vacuum hose dumping into the manifold)

too high a pressure (FPR not working).

Get all those checks out before doing anything else. Very important they are all checked and results noted.

 

oh and lastly prior monkeyed with AFM. Hopefully it has not been opened.

 

 

 

Edited June 28, 2019 by Dave WM