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cronoz78

AFM Suspect. Will I need a 7 pin/5 pin AFM??

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Hello all,

This is my first post on this site. I am having some issues with my Z. How do I even begin to explain...LOL!

Main Question(regarding my Thread title):

I may have to order a new AFM, after talking to MSA there are many... I have A31-625000 which is a 4 bolt (apparently more rare) and are almost never instock. Z CarSource asked me if it was 7 pin or 5 and I verified that it was 7 pin. But here is the funny part: 7Pin on the AFM and on the harness there are only 5 actual female connectors! What the heck! Inside the AFM is a working fuel cutoff switch. I ran though the AFM tests for the pins and everything seems to check out... I really dont want to mess around with this thing b/c getting one of these up to Canada is a pain in the butt and its not like I will get it next week... SO.. What do I order? A31-625000 which is a 4 bolt with 5 pin or 7pin? I did run through the AFM test and things seem to check out ok...

Background:

Car:

Stock 78 280z from the US now in Canada

120k miles

Goal: Get this car running tight. Or tighter at least. (how tight can a 70's car be? LOL) Possibly a mild upgrade of headers/exhaust and cam since its smog exempt, no cat, no O2. Might as well take advantage of that!

Issue:

-The car idles rough (blub,blub,blub,blub - exhaust note) not a smooth idle. I going to try and video this.

-Backfire is heard though under the hood (sounds like a quick pop/ crack) when engaging 1st and sometimes 2nd. Im sure the neighbors love that 6:45am LOL! Only happens once in a while driving but guaranteed to happen when car is cold and with in 5 min of driving.

-Had the car at the shop yesterday and the mech says: "Well, the good news is that its gutless" LOL Though he says he cant remember the last time he drove a stock Z. He used to AutoX them back int the day. "Power should be almost scary" he says as far as he can remember. My issue is that I have no point of reference regarding a good driving Z and a poor running one. But I do know there is an issue.

-Take your foot off the gas and the car decelerates rapidly, slamming your head back and forth and the gas pedal too! (only sometimes) but I think this is related to the dashpot at the throttle linkage which I will adjust or replace.

-This summer it just seems like it has a mind of its own, sometimes it drives nice but most of the time not. hehe.

-Smells slightly rich. I will pull the plugs and take a pic once I get some more driving on the new plugs.

What I have done:

-last night verified that the screen in the fuel pump inlet was clear. It has a aftermarket pump and there was no screen. Just had to make sure!

-Fuel pressure is 35-36 on idle and when the throttle is bliped it blips the pressure up to 39ish (PSI) and normalizes back to 36ish

-Changed both plugs (NGK BR6ES gaped to 0.040) and NGK wires.

-Did the ZX dist upgrade as per "Blue's" online instructions (Dist from Datsun parts LLC) Timing WAS set to 10deg @800. Original coil still there.

-Timing was verified yesterday morn at ~14 deg. We adjusted the idle down to 750ish RPM which bottomed out the idle screw. (Maybe today I will try to advance timing a bit and see.) Though I am afraid to touch anything as the car seems to run better than it has all summer right now, that gives you an idea how boggy it was! Right now I can drive it with more power than usual. The last time the car was driving "nice" I messed around with the dist timing and it did not help the backfire so I am hesitant the issue lies here.

-95% sure there are no hose leaks as I have replaced most of them.

-PCV valve cleaned with TB cleaner and is moving freely.

-EGR: Hose from exhaust manifold was never there but the hole was plugged. I finally got the rusty bolts (only ones) off the EGR to take a peek in there and found the inlet was plugged with some white stuff??? Anyways I removed it all now there is an open entrance to the EGR. To make sure that the EGR does not activate I removed the vaccuum hose from where the hose was coming from and plugged it. (Note: I sucked on the EGR hose to see if it opens and it does under vaccuum) But, essentially the EGR is deleted though I will fab up a plate to replace the EGR totally this wknd.

-Ran some seafoam through the throttle body, in the oil and gas tank. Oil is slightly brown now but still relatively clear.

-Im running mid grade fuel, I switched to that from premium cause it was running so crappy on the "GOOD" stuff

-Throttle switch replaced with a Newused one, cleaned and set to 1400rpm

-Fuel filter changed + hoses

-Idle air control valve was replaced a while ago (nissan part) by the PO.

-Had a leaking heatercore hose replaced them all the way to the engine. I had an air bubble in the heater core (you could hear it) dropped the coolant and bleed the cooling system for bubbles. I had an idea that the coolant was low (as i had seen in the rad and leaking from heater core hose) and due to this air bubble coolant was intermittently coming in contact with the coolant temp sensor causing ridiculous readings. I REALLY had that dream! That was the issue and everything would be fixed. Well it wasnt. BUT that can be an issue and it does happen and it would be a tricky one to diagnose! Anyways the leak was fixed.

-Replaced Coolant temp sensor to a Nissan brand this week

-Electrical conn's from the Thermotime/coolant temp sensor are not swapped at the bullet conn's (I chked at the ECU by unplugging one)

-Unrelated: I have a clunk coming from the back when changing gears 1/2/3. I installed a diff mount from technoversions and it didnt solve that... driveshaft can be turned a bit by hand

This weekend:

Im going to try an valve adjustment (prolly has NEVER been done).

Do a compression test

I have injectors/o-rings/seats on order (the originals are still on the car with minute cracks on the surface of the hoses)

Whoa that was alot of typing and remembering what I did so far. I am going to try and post a video of this thing idling.

I am really tempted to rip out all this stuff and swap to a carburetor set up. hehe (Woosaaah Woosaaah Wooosaaah - Scene from Bad Boys)

Any suggestions on where to go on this?

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Hello all,

7Pin on the AFM and on the harness there are only 5 actual female connectors! What the heck! Inside the AFM is a working fuel cutoff switch. I ran though the AFM tests for the pins and everything seems to check out... I did run through the AFM test and things seem to check out ok...

The pins that matter are the ones in the harness. Nissan apparently just left the extra parts in the AFMs after they stopped using the fuel cutoff switch.

-The car idles rough (blub,blub,blub,blub - exhaust note) not a smooth idle. I going to try and video this.

-Backfire is heard though under the hood (sounds like a quick pop/ crack) when engaging 1st and sometimes 2nd.

When you let off of the gas to shift or when you are accelerating?

-Smells slightly rich. I will pull the plugs and take a pic once I get some more driving on the new plugs.

-Fuel pressure is 35-36 on idle and when the throttle is bliped it blips the pressure up to 39ish (PSI) and normalizes back to 36ish

This is not right, the pressure should be around 29-31 at idle and "blip" up to 36 when you blip the throttle. Check the vacuum hose to the FPR.

-95% sure there are no hose leaks as I have replaced most of them.

I would try to get to 99.9%.

-EGR: Hose from exhaust manifold was never there but the hole was plugged. Anyways I removed it all now there is an open entrance to the EGR. To make sure that the EGR does not activate I removed the vaccuum hose from where the hose was coming from and plugged it.

Could have a vacuum leak here.

I have injectors/o-rings/seats on order (the originals are still on the car with minute cracks on the surface of the hoses)

Do you have injectors on order or just the o-rings and gaskets?

I am really tempted to rip out all this stuff and swap to a carburetor set up. hehe (Woosaaah Woosaaah Wooosaaah - Scene from Bad Boys)

Don't tell people that you're ready to bail out before you get started. It lowers the incentive

Any suggestions on where to go on this?

How long had the car been sitting before you got it?

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ZedHead

1) So either 5 or 7 pin will do

2) When accelerating

3) Ok but EF-37 in the manual says 36 psi but maybe I am misunderstanding it. So the pressure should never go higher than 36psi is what your saying then. I did check the Vac hose to the FPR but dont remember what it dropped to. New hose, no leaks there. Maybe I will recheck the FPR.

I forgot to mention that the pressure drops to 0 overnight.

4) Ok I take that one back, I am 99.9% sure there are no hose leaks as we did spray TB cleaner around all the hoses ect. Also it was checked by me and the mechanic.

5) I plan to totally isolate the EGR this wknd. to ENSURE no leakage

6) Injectors are on order as well.

7) Hehe that was a joke, Im in it for the long haul with this car It was so hard to find in its condition. I catch what your saying though.

8) Last owner kept it in his garage, only put Nissan parts on it, Drove it maybe once a week to work in the summer, he could have had better general maintenance on it. He had it since 2004 from the original owner (I even have the original bill of sale! haha) and he was an older guy not messing with stuff really and just took it to the mech when something was wrong and he drove it like a Camry.

I got last fall. I spent the winter changing hoses, cleaning connections general clean-up. It drove kinda sluggish last fall as far as I can recall. What started everything was last fall I drove it maybe 5 times before I had to put it away for winter hardly enough time to get to "know" the car. It was hard to start when hot (ie go to a store come out 20 min later and it wouldnt start or just turn over 6-7 times). This lead me to Thermotime sensor, coolant sensor, cold start injector (Everything checks out). It sat in my garage all winter (Nov-April) I started it about every 2 weeks let it get to operating temp and park it back (stored with fresh oil and fuel stabilizer). Once spring was here I could finally get it out and really work on it Fast forward to now.

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If you're only getting only one backfire, and your AFM tested correctly by the AFM procedure, you should probably hold off on getting a new AFM. Since I've been reading the forums I haven't seen many cases where the AFM was clearly bad. I seem to be the only one

(that I can recall right now) that had one that tested bad, ran bad (lots of backfiring, popping and stumbling at mid-throttle), and was definitely the problem, completely changing the way the car ran when I got a new one.

Yes, 36 +/- about 1 should be the high pressure, then the FPR will draw it down when intake vacuum is applied. So, at idle you'll see about 31, then if you remove the vacuum hose from the FPR it will rise to about 36.

The backfire and the fact that you bottomed out the idle adjustment screw are signs that you might have a vacuum leak. Don't forget that the crankcase is connected to the intake manifold through the PCV. So any leaks in to the valve cover or dip stick tube will end up as a vacuum leak.

And, apparently,the EGR can rot out internally, feeding exhaust fumes to the intake constantly. I don't know if this would cause your symptoms though. Here's the thread describing it - http://www.classiczcars.com/forums/thread40886-3.html

I would spend more time on the small stuff before going big on the AFM.

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Yes i agree on the AFM for now.

The incorrect FPR readings are probably a good cause for my high gas consumption

Have not had time to attack anything yet, and also I am waiting to see if I can get a Nissan FPR. If not will aftermarket do? What brand?

For starters I will try to do the valve adjustment tonight at wrk by pushing the car in gear as getting to the crank with a socket is near impossible especially when its hot.

I will check those areas for vac leaks as well

As for the EGR its has not rotted out like that guys case (very interesting thread though, thats what got me more interested in checking out my EGR to begin with)

Thanks!

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