Broken AFM...expensive part

[Funky-P]

Hey all, I just picked up a 77 280z a couple of weeks back which doesn't start. In trying to determine why I've found that the AFM failed almost all of the testing specs. I'm not sure whether this is due to tester error or not, but its an expensive part so I'd rather be sure that its the problem before trying to replace it. I was wondering if anyone had any advice or a functioning one that we could borrow to make sure that it is the issue.

Thanks, hopefully we can get this thing running soon.

[conedodger]

Find another and swap it out or send the existing one to Brett Industries in Orange, CA and have it rebuilt.

[webdawg1]

conedodger,

You have the contact info for Brett Industries (I.E. - website url, address, phone number...etc...etc) Have not been able to locate anything on them thus far using Google or other search engines...unless I just can't see the forest for the trees...

webdawg1

[Zed Head]

Hey all, I just picked up a 77 280z a couple of weeks back which doesn't start. In trying to determine why I've found that the AFM failed almost all of the testing specs. I'm not sure whether this is due to tester error or not, but its an expensive part so I'd rather be sure that its the problem before trying to replace it. I was wondering if anyone had any advice or a functioning one that we could borrow to make sure that it is the issue.

Thanks, hopefully we can get this thing running soon.

You might put your test numbers out here to be looked at. Some one could probably help you decide if they're terrible or not bad.

Your car should start and idle with a bad AFM anyway, as long as the fuel pump contact is working. Your 77 still has the contact in the AFM if it is stock. I would get it started and idling first, then you'll have a better idea of how bad the AFM might be.

[conedodger]

Mr. Head is correct. Are sure it isn't the Throttle Position Sensor? It has a setting for idle and WOT. Have you also checked the Cylinder Head Temperture sensor? If the wire is broken or the sensor is bad it sends an infinity resistance signal and the engine if it will run would be full rich. Lots of variables in EFI...

You just have to call directory assistance for Brett. The last time I was there was a decade ago and they were under the original owner. I had a website called PlanetZ and I used to make Turbo AFM for NA cars. Frankly it doesn't work very well, and I quit doing it.

[MikeO]

In response to the numbers... when we tested it it was getting 0 continuity through the ECU and 0 continuity at any point after we pulled it. As far as resistance we're getting between 11 and 13 on any of the pins, 6, 9, 8, 7 in any combination. The flap is the only thing working properly and displaying standard readings.

[Funky-P]

I'll have to check the tps and temp sensor, I just was checking in the order the fsm has to check and stopped at the afm as it was giving bad readings.

One thing is the engine will crank fine, but not start and it smells real strongly of gas almost as if it were flooded even though that doesn't seem like the issue.

[conedodger]

You should be able to put the AFM model number found on the side of it in an ad in the classified section here. If a guy named Daniel Parsignault contacts you, I have never gotten anything from him that didn't turn out to be near perfect so trust him. I (and Mr. Zed Head) are not saying the AFM isn't bad, it could well be. It's just that it really doesn't have a function during start and idle. Enough air bypasses it to start and idle.

A couple things that could make it rich and not able to start, one is if that wire from the cylinder head temp sensor found on the thermostat housing is disconnected or internally broken or if the sensor itself has gone bad. This tells the 'brain' that the engine is overheated and it calls for a 'full rich' path on the algorithm. A second would be if the injectors themselves are leaking or stuck in the open position. It doesn't take more than say one or two of them sticking to have a car that doesn't start as it just pours fuel in.

What does your fuel pressure do after you turn your key off? It should stay constant. If it drops you would have problems with hot start even if you could get it started and running.

It sounds like you have gotten a hold of a manual which is good. The problem is that although you find one problem, it doesn't mean you fix that and the car runs. EFI adds many levels of variables which can complicate figuring out what is wrong. The benefit to doing the more complicated job of figuring it out is that EFI cars are very drivable. This means they start easily, get good mileage, are happy no matter what altitude you drive to.

As for Brett industries, try calling 411 from your cell phone and when they ask for city and state say Orange, CA. That should get you the number. These are the guys that supply rebuilt AFM to Motorsport Auto and many others.

For injector cleaning and balancing I recommend RC Engineering or Marren (sp?). Check the back of Grassroots Motorsports for their contact info as they are both longtime advertisers. I have some spare injectors you can have, in case some of yours are bad. You send them your injectors and they rebuild them and clean them. Then they balance the flow. Makes for a very smooth running engine when you get them back and in. Cost the last time I did it was about $30/ injector so not dirt cheap.

[Zed Head]

In response to the numbers... when we tested it it was getting 0 continuity through the ECU and 0 continuity at any point after we pulled it. As far as resistance we're getting between 11 and 13 on any of the pins, 6, 9, 8, 7 in any combination. The flap is the only thing working properly and displaying standard readings.

Well, thanks for following up on the response. I'm not sure which test procedure you're using though. The procedure I've used is on Page EF-52.

You should get 180 ohms between 6 and 8, and 100 ohms between 9 and 8. Those are the two limits of the potentiometer and determine the feedback to the ECU from the flap position. If you're getting 11 - 13 ohms then you must be shorted somewhere. But then you shouldn't get proper readings from the flap. So we have conflicting results. Are you using a decent ohm-meter? 100 and 180 ohms are on the low side and may be out the range of your meter.

Between pins 36 and 39 you should get continuity when the flap is open. That powers the relay that powers your fuel pump.

Pins 6,7,8 and 9 should be tested to ground and should not show continuity. No shorts.

Are you connecting 12 volts and measuring volts out for your flapper test?

Have you confirmed that the fuel pump works and that you're getting spark?

It's good that you're digging in but you might be jumping too far ahead.

Edit - forgot to mention that you can take these measurements at the connector inside the car, with the AFM plugged in a grounded (or installed). The hardest part is figuring out the pin numbering at the connector but there's a picture in the manual, plus some of the pins are missing (not used). This way you test the harness and the component together.

Edited October 24, 2010 by Zed Head

[Funky-P]

Thanks for the info guys.

We went in and plugged it back in and checked the flap action which was good, but didn't recheck the resistance. It sounds like you are saying that it has to be plugged in to be getting the right resistance readings then? When I measured it originally I had it disconnected, which is how it is shown on EF-52.

I went through though and checked the water temp sensor, the fuel pump contact points, the EFI relay, the ground circuit. The fuel pump contact points were okay, but everything else was showing an open circuit. We noticed something that seems to be wrong, the negative terminal of the battery looks to just be connected to the starter and then to the body. Two grounds and no harness connection, which struck me as odd and clearly is not what the wiring diagram shows. So I guess tomorrow hopefully with some daylight we can try to figure out whats going on, there is a lot of rewiring done by the PO which may be the root of the problems.

I haven't had to deal with this sort of electrical issue before so I definitely appreciate the help.

Edited October 24, 2010 by Funky-P

[Zed Head]

You can do it either way. Still not clear on how you could be using page EF-52 but report "between 11 and 13 on any of the pins, 6, 9, 8, 7 in any combination." You didn't give any of your test values... 6 to 8, 9 to 8, 36 to 39.

Sounds like you're checking things, but you're not telling the values you're getting. Or whether you have power to the fuel pump, spark, etc. Are you looking for the magic loose wire? Most people confirm fuel pump power, then fuel flow, check fuel pressure if you can, turn the engine over, check for spark, etc.

Good luck, keep going, then come back later and re-read these ideas.

[Funky-P]

OK, I'm going to start over with the testing from the beginning and taking notes as to what all the readings are and try to check everything you've suggested. Then I'll post up my findings.