77 280Z Losing Pressure When Pressing Throttle

[REAP_]

Hey everyone I have a 77' 280z that has two major issues that I am currently aware of. The first is that im getting raw fuel on the spark plugs in cylinders 3 and 6, I'm assuming that those two are companion cylinders. I replaced the plugs, cap, and rodor and still had the same issue. I believe that the fuel injectors are stuck open. Any help with that would be great. As for the second issue I seem to be losing pressure every time I press the throttle down. Honestly when it comes to that issue I have no idea how to even start fixing that. The issue just happened this morning when I turned on the car to go get the flywheel machined. Any help will be greatly appreciated. Also I noticed that once the throttle was losing pressure the exhaust began to backfire. 

[Zed Head]

Your description is hard to figure.  It sounds like the engine still runs, and for some reason you decided to look at the spark plugs and saw that two were wet.  Describe how the engine runs, in general.  Does it have a miss?  Do cylinders 3 and 6 not work, you're running on four?  Need a more general idea of what you're trying to fix.

 

 

I can't tell what "lose pressure when the throttle is opened" means.

[REAP_]

The engine still runs and yes it is missing. I recently got the car about a week ago so I went in and replaced all of the plugs but as replacing them i noticed that the two were wet. The plugs on it before were extremely worn so I figured that may have been the reason for the misses. After replacing them is when I noticed that three and six were still coming up wet. The car idles fine and drives fine but this morning the issue of when i press the throttle Instead of picking up the RPM's or giving more power it feels like it wants to stall. Im trying to figure out why three and six are coming up wet and also why the the car is losing power when pressing the throttle. I figure that it may be the Air Flow Meter.\

[Zed Head]

The AFM would not affect just two injectors.  Don't get drawn in to replacing parts before doing the testing work.

 

Since the car is new to you, one thing that will help you greatly is to just examine all of the critical parts of the engine, the AFM, the distributor, the injectors, manifolds, etc., recording part numbers, and making sure everything is connected correctly and intact.  One reason people sell their cars is because they messed things up so bad that they can't figure them out any more.  Then they sell the car, still messed up.

 

Make sure the injectors have the right part numbers, and are the correct color for an NA engine.  I picked up a wrecking yard engine that had a mixed set of wrong injectors.  People get desperate when their engines don't run tight and do crazy things.

 

The Engine Fuel chapter of the FSM has a series of simple tests you can run to figure out what's wrong.  The lack of acceleration and the backfiring could be the AFM, or fuel pressure, or clogged injectors (maybe four are clogged and the PO made everything rich to compensate), or timing, or crossfire between plug wires, incorrect firing order.....many possibilities.

 

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

[REAP_]

changed plugs when bought car 3 and 6 are black with raw fuel, believe injectors are stuck open, todays issue that started to happen was when i went to give it gas it would just bog out no response as if it was running out of gas release throttle and it idles fine leining towards M A F issue ? 

[REAP_]

zed head did tht car was running and able to be driven, just this morning started with the no response to throttle acceleration, from what i can figure so far the maf is going bad 

[Zed Head]

Sorry REAP, but your communication skills have diminished dramatically from your first post;  misspellings, punctuation, grammar, odd phrases like "no response to throttle acceleration".  The throttle doesn't accelerate.  I can't figure out what you're trying to say.

 

Seriously, I know you're on a phone somewhere texting, hopefully not while driving, but your posts don't make sense anymore.  Put time in to the message and you'll probably figure things out before posting.  I've solved a lot of problems just by trying to describe them.

 

Feel free to replace the AFM, but you're probably wasting money.  You can spend time on testing, or time AND money on replacing parts.  The first is cheaper and more effective.

[siteunseen]

 

'77 had a recall for the EGR tube coupler going into the intake manifold coming loose.  Mine had a golf ball size hole rotted in the tunnel.  Created a HUGE vacuum leak.  Take a mirror and look under the manifold towards the back (windshield).

 

 

EDIT: The picture with the mirror is an example.  That's actually the new intake, I was showing someone the heat shield bolts location.

Edited April 10, 2015 by siteunseen

[siteunseen]

Another thing to check is the sweeper in the AFM.  Pop the black plastic cover off and make sure it's not stuck by tapping the counterweight.  Here's some images.

 

http://atlanticz.ca/zclub/techtips/afm/index.html

[FastWoman]

I'm guessing that "losing pressure" means "losing power," so when the OP steps on the accelerator pedal, the engine bogs and backfires out the exhaust.

 

I would bet money that there are multiple problems that have to be solved one by one.  The first is the question of why #3 and #6 plugs are wet.  No, they are not "companion" cylinders in any sense.  QUESTION:  Do the new plugs in #'s 3 and 6 show any combustion deposits, or do they look like brand new plugs soaked in fuel?  If they are deposit-free, I would suspect an ignition problem.  I would replace the spark plug wires, if possible with NGK brand.  (You've already replaced everything else from the coil forward.)  I would probably do this on a new-to-me vehicle anyway, as plug wires do have a limited lifespan, and most people neglect to replace them.  Your wet plugs in #3 and #6 would easily explain the backfire, as you're blowing raw gas and air into the hot exhaust, which occasionally ignites/explodes there.  (This can damage your exhaust, BTW, so you want to fix the issue quickly.)

 

If you've got combustion products on #3 and #6, then you might be dealing with fuel issues, e.g. stuck injectors.  QUESTION:  Do you have fresh gasoline, or are you trying to run the car off of the gasoline that came with the car?

[EuroDat]

Having a little trouble following your post. I agree with Zed Head. Take some time to read you posts before posting. Makes it easier for us to follow and gives you a better chance of resolving your problem.

If you suspect a leaking injector I would start by investing in a cheap pressure gauge that can read up to 50psi and mount it (with a tee piece) between the fuel filter and the fuel rail that runs above the injectors.

If you suspect leaks and losing pressure you can test sections of the fuel system for leaks. Run the engine to get pressure, stop it and check the gauge for pressure drop. You can also build up pressure by activating the fuel pump with the AFM.

When its stopped it may drop, but it should be very slowly. Mine holds pressure good and drops 10psi over a couple of weeks. If it leaks down quickly, try clamping off sections and see if it slows or stops or slows the pressure drop. Use vice grips with two metal plates so you don't damage the rubber hoses. If the hoses are old and hard you may want to change them first.

Things to clamp off are;

-The fuel line aftrr the filter, before the gauge. Tells you if the check valve in the pump leaks.

-The line after the fuel pressure regulator. This is the Return to tank line. Tells you if the FPR is leaking.

If these two test have no effect on the pressure drop, then its in the injectors or the CSV (cold start valve) located a little behind the throttle body.

Im not saying this is your problem or the only problem you have, but its easy to install and you can learn a lot about the condition of the fuel system.

Chas

[TomoHawk]

The first thing I thought of was a bad FPR or its vacuum source not working, causing a lean condition with an open throttle.

 

OH- and stop using the word ISSUE when you are talking about a PROBLEM. Issues and problems are not synonymous.