Okay, so I bought a fuel pressure guage, I have the fuel pre

[Guest Anonymous]

Last night I purchased a fuel pressure guage and tested the fuel pressure this morning, it looks perfect, right about 36. I revved it with the guage on to see if the pressure dropped when it started back firing through the intake, it didn't drop so the pressure if perfect. Now, I did notice something, it almost seems like it runs fine when it's really cold but when it starts to warm up then I get the backfiring through the intake and the bad revs. I could be wrong, that's just what it seems like. Now that I've established good pressure, where do I look from here? The only thing I can think of now is a bad AFM. What else could it be? For those of you who haven't been reading the previous threads of mine, here's what I have done so far.

 

Flushed the fuel tank

Replaced the injectors

Replaced thefuel pressure regulator

Checked the fuel pressure, it's perfect

New fuel filter

 

The AFM adjustments still stand, when I adjust the wheel on the AFM (to run richer)it runs perfect but this causes me to fail emissions. This is quite frustrating but I think I'm fairly close to figuring out what it is now that I've established that the pressure is good. Any thoughts?

 

Chris

[David K]

Its gotta be the something along the lines of temp sensors or the afm. If you temp sensor is bad, you will have the same problem that i was having. The car runs great at cold because it will run rich because of a faulty sensor. When it gets up to temp, the mixture will not be right because the temp is not sending the correct temp reading.

 

While you are int he engine bay, rev the engine to 3k/or until it starts popping and then just MOVE the weight on the spring inside the AFM. SLOWLY move it back, and move it foward and post back to let us know what direction made the engine run smooth.

[Guest Anonymous]

The temperature sensor, eh? What is the exact name of that? Is that the one bolted into the thermostat housing? I know when I move the mechanical wheel on the AFM counterclockwise (richter) it runs better and it'll stop backfiring through the intake. It takes about 14-16 notches for it to run really good. And like I said, it seems to run better when it's cold, but when it warms up a little bit it starts backfiring through the intake when I rev it (with the AFM stuck at the stock position). When I say cold I mean like the first minute or so of start up. Thanks for the input, keep the replies coming, I really appreciate it.

 

Chris

[David K]

Ok there are 2 ways to adjust an AFM. One is to adjust the spring tension. The other is to adjust the small arm that is on the AFM weight that we are talking about. Try setting those in harmony. It took me a very long time to figure out how to do this, even though many people attempted to explain. Its one of those "you have to be there" type of things. There are many other Z guys in Phoenix. Do a search and locate some of them, or maybe post a request for help from guys in your area. I bet they would love to help.

[Guest Ian turbo240]

First of all, you should never have to move the wheel inside the AFM for any reason. AFM's just don't go bad like that. A bad AFM will usually have a "spot" in it where the electrical contact is bad. It will never suddenly run the engine lean over the whole rev range. You do not have a bad AFM IMHO. What you need to look at are the coolant temp sensor, like David said, or look for vacuum leaks. Check to make sure that the EGR valve (if equipped) isn't stuck open. This would cause the engine to run poorly. You should be able to push it open with your finger and make the engine either run worse or die. Check for other vacuum leaks by spraying carb or brake cleaner on the intake near the head and other places where leaks could occur. Also, check to make sure that the rubber boot from the AFM to the throttle body is in good condition. Any cracks that go all the way through, and it should be replaced. Check all of the electrical connections to the sensors and injectors. If you have a bad connection to the CTS, this will cause poor running conditions. Good luck!!!

 

Ian

[Guest Anonymous]

Could you try your best to explain how to do the 2nd adjustment on the AFM? Also, where's a good place to check for vacuum leakes? Would a vacuum leak causing a lean idle and backfires through the intake? Wouldn't the idle be higher if there was a vacuum leak? Those temp sensors sound like a good thing to check.

 

Chris

[Guest Anonymous]

It's a stock 1978 280z by the way.

 

Chris

[280Zone]

Chris, Yes a vacuum leak will cause a lean condition. The bad news is that leaks can be a lot of places.

[David K]

The AFM's job is to administer the amount of fuel to the air coming through the AFM. There is an arm that moves along what looks like a computer board. That is the fuel part of the AFM. Now, the brass looking weight the arm is attached to is where i am going to have you look. There is a tiny screw that holds that weight in place. You can loosen that and adjust the amount of fuel that is dumped into the engine. You will notice, as you move it, the engine will smoothen out, or start putting....................

 

YOU KNOW WHAT, i am going out to the garage right now to get an AFM and i will post pics for you when i am done. Dont mind what i said above.

[David K]

Ok, with all due respect to the request of HybridZ admins, i wont post the pic here, but will provide the link.

http://socalz.org/afm%20copy.jpg

 

Now, the red arrow is where you adjust the tension on the spring. The tighter the spring is, it will provide the engine with less fuel/air. When this happens, the engine will starve itself if the AFM spring is too tight. The more slack in the spring, more fuel/air would be given to the engine under rpms. If it is too loose, the slightest rpms could make the engine run very rich, or even bog down from being too rich. The spring has to be set in a precise spot in order for the engine to run as it is supposed to.

 

Now, the yellow arrow points to where you can adjust the amount of fuel given to the air, which in turn creates the correct air/fuel mixture. If you will notice, you can see the arm that swipes along the computer board down at the bottom. That is where the reading for fuel is sent to the ecu.

 

This is how you adjust these two in unison. First, set the spring to where it should be by running the engine at normal operating temps. You will either 1)have rough idle, or 2) have a good idle. Now, if you have a rough idle, give or take on the spring a little. Try tightening it, or loosening it, whatever way works to smoothen the engine out. Now once you get it idling smooth, you move on to higher rpm settings.

 

Rev the engine to about 4k. Yes it will be loud You will tell if the fuel mixture arm needs to be adjusted if it its missing and popping. While you have it at 4k, and it is not running correct, adjust the arm that the yellow arrow points to.

 

Hopefully, if your AFM is good, this will make the engine run smooth and have power throughout the rpm range. But i must insist that you check your temperature sensors first and check for vacumm leaks. The most common leaks are at the AFM to Throttle Body rubber boot. You can also find more on the hoses on top of the Intake manifold.

 

Your intake/exhaust manifold may also be bad.

 

Good luck Chris.

[Guest Anonymous]

It sounds like there might excessive deposits on the intake valves.Excessive deposits will "absorb" enough fuel to cause a lean condition.Adjusting the AFM will only treat the symptom not cure the problem.

[Guest Anonymous]

Engine had a valve job done on it about 6 months ago, hasn't been driven all but 300 miles since that. I'm not quite sure what a valve job entails as I have never done one but I know it had one. It basically had a major tune up as well. I appreciate that photo of the AFM, I will fiddle with that tommorow night. What was the exact name of that temperature sensor? While all of this is frustrating I am certainly learning something. I'm going to stick with it until it's fixed, I really want to start driving this thing.

 

I guess at this point it's time to start replacing the cheapest parts first, Coolant Temperature Sensor is 20 bucks. I think I have someone that will loan me an AFM for a 78 280z to test, and will sell it to me if I need it. I will go get some carb cleaner and spray the hoses and intake and such. I'm not sure what else to look for on a car with 83,000 miles.. that's just barely breaking it in.

 

Chris

[David K]

does your head have a temp sensor on the passenger side of it? You should change that one before you change the coolant temp sensor.

[Guest Anonymous]

While I haven't worked on the 280z since I checked the fuel pressure, I have been talking to a friend of mine. We were chatting and I was explaining to him the sounds and things such as that I hear in my engine. One of them is a hissing sound coming from the upper drivers side of the engine bay. Then it hit me, my brakes are really really bad in that 280z, almost like the power brake booster is giving out. It feels quite like when the power brake booster went out on my Camaro. I have a funny feeling the power brake booster is shot causing a massive vacuum leak in turn causing my lean condition. Adjusting the AFM by 16 notches was a band aid for this. While I haven't yet gone out and tried disconnecting the power brake booster, I will do so tommorow. It makes perfect sense. What are your thoughts?

 

Chris

[280Zone]

Well, that could be it, what you describe would be a vacuum leal and could be the cause of your problem. Good Luck

[Guest Anonymous]

Yeah, I'm going to try and see tommorow. I'll keep you updated (for those who care). Have a good night guys.

 

Chris