stumped

[78blackpearlz]

well guys I got lucky and got the new ICM early and installed it today... Unfortunately, my luck ended there however.. Put in the new ICM and took it out for a test drive and it drove really smooth for about a minute and backfired horribly then drove smooth again. So I was hoping it was just one last pop to end it all so kept on going and it drove smooth for a little while but started to do it again just not as bad.  

[Zed Head]

That's a bummer. 

 

Does it pop back through the intake manifold (under the hood), or does the bang come from the exhaust pipe?  It's really best to be methodical and meticulous when you get one of these types of problems.  Lots of detail in descriptions, even on the small things.  Even the stuff that seems completely unrelated like the tachometer needle behavior, noises from the radio, lights that flicker, the voltmeter needle, etc.

 

Descriptions like "I have run a fuel pressure test on it and everything was alright." aren't enough.  Numbers are best.  Some people think that loosening a hose clamp and seeing fuel come out means pressure is okay.

 

When was the last time it had a tune-up?  Plugs, cap, wires, etc.  Some of use have spent lots of time just find that the plugs were worn out.

[78blackpearlz]

Ok ill try to describe it the best I can. When I drive in the heat my car will try to stall almost like all the power from the engine is just gone. It used to only do it coming from a complete stop but lately it has started doing it from first to fifth gear but from third and up it will only do it if I give it a little extra gas. But when the car almost stalls it will have a backfire from the exhaust ( technically an afterfire I think) with no smoke. After the afterfire the car will come back to life and take off like a rocket. But soon start to sputter until I get to a cruising speed and do not have to give it much gas.

 

 

I hope all of that makes sense. But I do want to run another fuel pressure test on it. I ran the test last summer trying to figure out the same issue so I don't recall the exact numbers. I did do a tune up about a month or two ago (plugs, wires, cap, and button). I did have the clutch replaced the winter before this issue began but I talked to an ASE certified mechanic and he couldn't think of any way the clutch could be causing the issue but I trust you guys a little more about these things so I figured I would add that in there.

 

That's about all there is. I do have one other question though, is it possible to have a partial failure in the fuel pump. I ask because during my test drive yesterday I noticed the fuel pump was whistling not its normal humming and when I got in my car to go to work yesterday morning it was doing its normal hum all day and I never had an issue with the hesitation I guess is the best way to say it.

[Zed Head]

 When I drive in the heat my car will try to stall almost like all the power from the engine is just gone.

 

But when the car almost stalls it will have a backfire from the exhaust ( technically an afterfire I think) with no smoke. After the afterfire the car will come back to life and take off like a rocket. But soon start to sputter until I get to a cruising speed and do not have to give it much gas.

 

is it possible to have a partial failure in the fuel pump

You'll probably feel like I'm overdoing this point, but "in the heat" is too vague.  One person's heat is another person's fine day.  You're also not telling us how hot the the engine is, is it fully warmed up, or is this right after starting out?  It's the engine heat that matters, and how hot the other components are.  Heat builds up everywhere as the engine runs.

 

Fuel pumps can fail when they get warm, but you can also have crud in the tank clogging the pump inlet.  Since your problem is repeatable and the car is driveable, it's a great candidate for installing a gauge and letting it hang out of the hood where you can see it.  Looks bad but it will tell you a lot.

 

The car might be taking off like a rocket because you're pressing the throttle hard to try and make it run.  No offense, but people who aren't in tune with how engines work will do things like that.

 

There are other simple tests that you can try but fuel pressure is very important and should be verified before looking elsewhere.  You can get side-tracked.

[siteunseen]

What's the tach do when it acts up? Does it hang or stay with the motor?

Learned that from Zedhead.

[78blackpearlz]

I wont complain about detail you have helped me a lot here and I've learned a lot from you and a lot of other people on here. By in the heat I mean from about 85+ degrees in Alabama so its a very humid heat.

 

 No offense taken, but I don't pedal to the metal it. When it decides to do it I let the gas out and push the clutch down and coast it till it decides to run again. Engine temperature effects it but it will do it with the engine not at running temp which on mine (because I've noticed a lot of people have different temps on their Z that it runs at) is just below half around 170-180 I assume.

 

I have had the tank cleaned it was actually one of the first things I had done when I got the car around 4 years ago.

 

The tach will hold steady at the rpm of the engine. I have noticed that all the gauges hold steady when it is happening (always paranoid when driving so I watch my gauges like a hawk)

 

But little more info one the issue, while driving back and forth to work that it has gotten better since replacing the ICM it doesn't do it near as much or near as badly just under load it still will.  

 

Thanks again for all the help.

[Patcon]

If it is an "after fire" as you describe then I will toss out a theory for thought. What if the loss of power is an event where fuel is not being burnt and being dumped into the exhaust and something hot like a cat or hot muffler pipe or flange is lighting it off and then for what ever reason the fuel starts burning again and the power comes back?

[78blackpearlz]

Well I can say for certain its definitely not the cat because it was taken off long ago. But if that was the case wouldn't there be some sort of smoke coming from the exhaust?

[Zed Head]

I had a similar thought to Patcon's that's why I asked about a tuneup.  You need coil discharge for the ECU to tell the injectors to spray fuel so I thought maybe you were losing spark somewhere between the coil and the plugs, but the coil was still discharging.  Maybe a short from the main coil wire to ground.  Could also be that the coil is bad and doing enough to trigger the ECU but not enough to spark the plugs.

 

I hate to throw suggestions out though, because you can spend a lot of money replacing parts trying to find the right one.  That's why we were suggesting the module cooling, it's a good test.

 

So, it seems like you are losing spark, but maintaining fuel.  That's the odd thing.  You might just closely check all of the wiring at the coil, and the distributor cap, to make sure you don't have a wobbly wire.  Don't let the wires lean on or touch anything, keep them well-separated.  Pull the main wire out of the coil and cap and reseat it to make sure it has a good connection.  They've been known to seat poorly, causing problems.

[FastWoman]

IF the tach keeps steady with the RPMs of the motor, then your ignition is good at least as far as the ICM.  Your coil, distributor, rotor, wires, and/or plugs could still be failing you.  Of these, only the coil would be temperature sensitive.

 

Try this:  Switch your radio to AM, and find a fairly quiet, static-free frequency that lets you listen to the ignition.  You might need to turn up the volume a bit.  You'll hear a variable-pitched whining noise.  Take your car for a drive, and try to reproduce the loss of power.  As you lose power, does the whining noise drop out?  Be watching your tach at the same time to see if your RPM indication drops out.  If your RPM indication doesn't drop out, then your ICM is good.  But if the whine drops out, you probably aren't getting spark, most likely because of a bad coil.  (Note:  I've never tried this diagnostic procedure nor heard it described, but I still think it should work.)

 

I think Charles' (Patcon's) theory about loss of power and afterfire is a good one.  What doesn't make sense to me, though, is how an afterfire would have any impact on engine functioning, as it is entirely an exhaust event.  Unless...  is there any possibility your exhaust valves are messed up?  Maybe they are hanging partially open, causing you to lose compression and therefore power, until enough raw fuel makes it to the exhaust manifold to detonate and cause the hanging exhaust valve(s) to slam shut.  It's a long shot, but I thought I'd throw the theory out there.  Might be interesting to do a compression test.

 

Question:  Are you SURE it's an afterfire and not a backfire (through the intake)?  An afterfire will sound more like a pop or bang (like a gun going off), while an backfire will sound like a muffled "thump" under the hood.  The reason I ask is that a backfire will slam your AFM closed and shake the engine, making it more likely than an afterfire to cause your engine to suddenly run better.

[Zed Head]

Ya know, we have't given blackpearls the boilerplate advice on the 280Z EFI.  He'll probably have to dig in and learn some auto to get it fixed.  It would have been nice to get a quick resolution but odds are it's time to go through the rigor of testing the system with a meter and gauges.

 

There aren't many mechanics out there today who know how to work on these old cars.  Say you were a mechanic who knew how 20 years ago, when these cars were 15 years old.  15 years is already old technology.  Now, 20 years later, those guys have retired, replaced by code readers and sub-system replacers.  It's just how the industry has gone.

 

Anyway, the Engine Fuel, and Engine Electrical, chapters are the place to start.  There's also the Fuel Injection Guide, very useful  Many have started from this very point.

 

http://www.nicoclub.com/FSM/280z/

 

http://www.xenonzcar.com/s130/other.php

[78blackpearlz]

Ok everyone thank you for all the help. I really appreciate it.

 

Zed Head, I thought the ignition was a part of the issue but now that the ICM has been replaced everything in the system is at most a year old now minus the switch. I will double check all of the wires, cap, and button to make sure they are all seated correctly in the morning and I will read the EFI bible until I know it by heart.

 

FastWoman, you mentioned the valve sticking open and it kind of made me feel stupid because it dawned on me that my I do have a slight valve tick to it. So I did some research and found another post on here where you had commented telling the valve clearance for the 280z's and it helped a lot because doing some more research I learned that it is recommended for the valves to be adjusted on them every oil change. And to answer your question about it being an afterfire, yes I am totally sure it is. I am pretty sure i have scared some people while driving down the road because it sounds just like a gun shot.

 

I do have one question though, if the exhaust valve is sticking open will adjusting the valve help or is there something else i need to do? I want to do this anyways because it is long past due. I do not believe it has ever been done to my car and i hate to say it.

 

Sorry about the late reply.