77 280z running like poop

[ZDrummerGuy]

I have a 1977 280z with running issues. What's wrong is that when I start the car, it cranks over fine and will start fine but after the initial start it will immediately bog down and either die or run on like 3-4 cylinders :sick: It helps tons when I push the AFM in about 25% of the way, but If I let it go on its own the car sputters and bogs down again or dies. With the AFM pushed on full (the top cover is off) I can slowly push the car up to a fairly high rpm, 5000 or so, but I can't seem to do quick revs or the car will backfire even with it in all the way.

Here are some of the things I've replaced:

-New cap and plug wires (with relatively new plugs; they're NGK, don't worry)

-New fuel filter

-New seals for the fuel injectors

-New fuel regulator

-New coil

Here are some things I've done:

-Cleaned the fuel lines

-Set the timing

-Tested the fuel pump (It works and puts out about 36 pounds of pressure between the new filter and the rail)

-Tried a different ECU and a different AFM (Both came with the car and both give the same results)

-I did do a compression test awhile ago and everything was fine, and I should be able to do another compression test tomorrow afternoon

-I checked to see if the injectors work by taking them fully out of the car starting it and see them all work correctly

-I did check the voltage of the clips going to each of the fuel injectors and those all work fine

-I checked the points in the ECU that go to both the AFM and the fuel injectors both also came out fine

-I checked the electrics in the AFM itself and everything seems fine (it's also possible to hear the fuel pump working when the AFM is puched in slightly)

If anyone has an idea of what might be going on please reply, I feel like by now everything should be working at least sort of correctly. I'm at the point where digging into my pocket and sending it to a mechanics shop or buying a Megasquirt system would be better than wasting anymore time on it. Would maybe replacing the whole AFM do me any good? Could it be a bad sensor sending a bad signal to the ECU? I appreciate anyone's input!

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[EuroDat]

When you say you checked, do you mean checked by following the FSM of FI Bible? The so called bible has a great diagnostic section you can go through with the FSM. Just need a multimeter and some cable to do voltage tests. Only needs a bad connection to mix up the ECU.

Here is a link to the FSM and the "FI Electronic fule injection guide" is in the Others section further down the page.

XenonS30

Chas

[siteunseen]

Backfiring out the tail pipe and sooty = RICH, not enough air. make sure the air filter and piping are clear and clean all your electrical grounds, http://atlanticz.ca/zclub/techtips/electricalconnections/index.html

Backfiring out the Throttle Body = LEAN, too much air. Vacuum leak can be found by using the "yogurt cup test", put that in search box up top.

[FastWoman]

When you push the AFM open, what you're doing is delivering more fuel (and the same amount of air). In other words, you're richening the mixture by pushing the AFM flap open.

Considering you've already replaced or tried swapping everything, I think you probably have some vacuum leak issues (probably big ones). You should start by replacing every inch of vacuum line. Then check for vacuum leaks with the "yogurt cup test." After you've eliminated rotten tubing, the following common leak sources are left:

-- Intake manifold - to -head junction, especially around #1 and #6

-- Bad power brake booster

-- Ripped/cracked "accordion" boot between AFM and throttle, resulting in unmetered air

-- Disconnected or improperly connected vacuum lines

-- Leaking items connected to vacuum lines, e.g. mode selector switch for heat/AC system (which can be re-furbed very easily)

Have you checked your throttle position sensor? It's the little square, black switch assembly on the side of your throttle. It should be adjusted per the FSM.

You might also have an ECU drift issue. The Hitachi ECUs ('78 and I believe also '77) tend to drift leaner and leaner with age. This can be corrected by adding the right resistance to the coolant temp sensor circuit. If you do want or need a new ECU, Superlen has been working on one specific to the Z and will be releasing it pretty soon. The intent is that it will be plug-and-play, or as close to P&P as is feasible with these old cars. It's called "Hellfire," and there are a couple of current threads about it.

[ZCurves]

Looking for a similar problem myself... I did the old 'Screwdriver To The Ear Test' on each injector. Discovered my number one injector had failed. I also created a test lamp and confirmed that there was a pulse being sent to the injector - just that the injector had seized. Now I am replacing that injector and resealing the rest....

[FastWoman]

Andrew, it's perhaps an occupational hazard (former neurobiologist), but I can't think of the "screwdriver to the ear test" without thinking of Phineas Gage:

Phineas Gage - Wikipedia, the free encyclopedia

My son told me over the phone about the old screwdriver trick, and I immediately ordered him a mechanic's stethoscope, which works a TON better than a screwdriver and is also safer -- and probably even cheaper. Harbor Freight -- best few dollars you'll ever spend on a tool!

[EuroDat]

That screwdriver trick is often mentioned in older factory service manuals. Its even shown in our FI Bible on page 36LOL

Ive used it at work on a homogenizer we use for cell breaking. The young guys thought I was crazy, but I found number 4 vavle had something in it and it did, an o-ring. That shut them upLOL

You are right Sarah, The mechanics stethoscope is 10 times better, but if you don't have anything else a screwdriver will do.

Edited April 8, 2014 by EuroDat

[ZCurves]

Yes, I have the stethoscope but I was too lazy to walk into the garage. Besides I enjoy getting grease in my ear from the screwdriver handle!

[TheGrimOne]

Have you cleaned the throttle body since you have had the car ? does the IAC help at all ?

[tcacars]

I basically had a car doing the same thing. We changed out the temp sensor that goes back to the ecu and it ran a lot better. Then I got a variable ohm resister and put it inline with the temp sensor and was able to regulate the amount of fuel going thru the injectors and it ran great, plus it was fun to play with, but be careful not to run it too lean. If you need extra parts I have three complete intakes and afm, two complete cars, a built L28, two 4 speeds and need to sell it all, I don't have time to do anything with them. Pictures are on my webpage www.tcacars.net Hope this helps.

[siteunseen]

That potentiometer trick made mine my '77 run better than anything. $5 at radio shack wired into the cabin for fine tuning. Now to measure the resistance and get one you have to adjust with a small screwdriver for the permanent fix.

[rcb280z]

I thought you couldn't adjust it on the lean side. If you are adding resistance aren't you making it run richer?