My Z is bogging down

[grantf]

For the last 10 days my 77 seems to be loosing power. It idles just fine and revs great. But under load it has does not have any power. Uphill is the worst. it seems to be getting worse and I can hear a whistle from somewere forward of the drivers seat. Its hard to pin down because it only does this under load but not at idle. A coworker suggested it may be a clogged catalitic, but I am not really convinced, I am not discounting it ether. I have found no smoking gun in the vacuum leak department other than the bad PCV hose. It is sealed up with a tempory fix till the new one arrives.

I dont think it's fuel delivery (not discounting it yet). Anyhow I am sort of at a loss of were to start. My car has been running great for about a year now since I last chased down some EFI culprets. oh and all cylinders are operating (pulled each plug cable out one at a time).

[grantf]

Hmmm I am just thinking a little bit.......

I dug out my old drivers side sun visor that states:

"A catalitic converter is used in this model for cleaner air. The following instructions should

be observered to AVOID LOSS OF FUEL ECONOMY AND DAMAGE TO THE CATALYTIC

CONVERTER

* DO NOT RACE .............

ect. ect."

So I believe I do have a cat and not just a resonator. I am thinking about removing it and putting in a strait pipe as a test. I do not have much experiance working with exhaust. the cat has been welded in. could I put in a strait pipe with clamps to test?

By the way my car had been running rich for quite some time, I have heard that this is bad for catalitic converters and my tranny tunnel does get really hot.

Edited June 23, 2012 by grantf

[rcb280z]

Check your vacuum with a gauge. Check fuel pressure. Then post results. Don't know what your smog laws are in Seattle regarding removal of cat. Your 77 has a floor temp warning lamp correct? If it is working it will light up when the cat gets too hot. I have a fairly new cat in my 77 and the tunnel gets warm but that's normal. Make sure the heat shield is still there also. How rich was it running? Was your mpg low? Also check timing and see if your vacuum advance is working.

[grantf]

Check your vacuum with a gauge. Check fuel pressure. Then post results. Don't know what your smog laws are in Seattle regarding removal of cat. Your 77 has a floor temp warning lamp correct? If it is working it will light up when the cat gets too hot. I have a fairly new cat in my 77 and the tunnel gets warm but that's normal. Make sure the heat shield is still there also. How rich was it running? Was your mpg low? Also check timing and see if your vacuum advance is working.

I made a pretty extensive EFI tune up on my car about a year ago. The car has run pretty good till now. Before the tune up it was running way rich, I had black deposits on my rear bumper and left tail lens.After the adjustments my MPG went from about 9 to close to 20. tomorrow I plan on making the usual tests, fuel pressure and vacuum. also I will check my AFM for proper function. My car is exempt from emissions here in Seattle.

[240260280z]

I agree, probably a vacuum leak where it whistles. It may be in the brake booster.

1st thing to do is to check your plugs. Too much fuel and plug fouling will bog you down.

2nd thing is to check fuel pump. Not enough fuel under load will cause bogging.

3rd thing is ignition. Ignition systems often fail at higher rpms.

[grantf]

thanks blue.

So today I replaced the PCV hose. This was a cause of some problems. I ran the engine, the engine did not like to rev past 4000 rpm. the engine wold shake and a unusuall noise came from the AFM. I removed it and found that it sticks at about 60% open. also the vain is bent. I have seen this happen too others on the board. I need to think this one through a little in order to try to rectify the problem. here are few pics:

I have not checked the plugs yet, that is next.

I have not checked the fuel pressure yet that will also happen when the AFM is put back in

I have not tested the vacuum yet that will come after the the fuel pressure.

I do not think that my AFM being in its current condition is helping, but I am not convinced that it is the main culpret.

Edited June 24, 2012 by grantf

[grantf]

So I straightened the air meter flap as best I could and found that the sticky area was were the inner flap rubbed inside the top section. I found this out only by removing the waffle side cover. It moves smooth now.

But Alas this hase not solved the main problem.

I have checked the spark plugs 1 through 5 looked light grey with a little build up. 6 looked tan. All were dry no gas or oil.

My vacuum read 10 hg at the heater control tube and 10 hg at the brake booster tube. So I am ruling out a brake booster leak. I know this seems to be low vacuum, my car has always been under 17. I just can not seem to find any leak, I even sprayed carb cleaner around any place I could think of and no increase in idle.

My fuel pressure with the car not running reads 40 psi and 37 psi while running.

I am starting to get bumbed. I am running out of tests and dont know where to go from here. Bad Cat?, blown manifold gasket?, blown head gasket? :ogre:

Edited June 25, 2012 by grantf

[Zed Head]

How is your ignition timing; static, vacuum advance and mechanical? Have you checked the breaker plate in the distributor (it allows the vacuum advance)? Maybe it's stuck. You can get a good idea of if things are working by watching a timing light and disconnecting the hose to the vac advance canister with the throttle off-idle (to open up the port), then leaving it disconnected and revving it up (to move the centrifugal advance).

Retarded timing would cause a power loss. I would spend some time verifying things are working in the distributor.

[240260280z]

Plugs don't look too bad. You should stick with NGK in the future.

Do you have Bosch wires? If so they are 100% crap. I wasted $70 on a set an they sparked through the insulation on damp days after 4 months on my old RAV4.

Good find with the AFM.

Check the timing like Zed Hed says then report back.

[grantf]

My wires are Beldin. I have been meening to switch to NGK plugs for a while just haven't gotten around to it yet.

I put the timing light on the car today. I am 13.5 deg advanced, idle at about 850 rpm.

I also checked the vacuum advance on the dizzy using the mighty vac, it advanced and seemed to hold a vacuum at about 10 hg (I dont really trust my mighty vac that much so for most measurements I am using a dedicated vacuum gauge).

I also pulled the hoses from the NPT valve and EGR. Did not make a bit of difference at idle, though I noted that the NPT to EGR tube spit out what seemed like warm exhaust with trace fluid, most likely water.

I am thinking that my manifold gasket is leaking, the engine sounds a little like it did before I replaced it about a year ago: http://www.classiczcars.com/forums/thread43150.html

I just don't know if this can account for the major loss of power I am experencing and why I would blow a new gasket after only one year.

I drove the car around the block again, under load it does not like to rev past 2500 rpms at idle it runs really rough at 4000.

still stumped.

Edited June 26, 2012 by grantf

[grantf]

How is your ignition timing; static, vacuum advance and mechanical? Have you checked the breaker plate in the distributor (it allows the vacuum advance)? Maybe it's stuck. You can get a good idea of if things are working by watching a timing light and disconnecting the hose to the vac advance canister with the throttle off-idle (to open up the port), then leaving it disconnected and revving it up (to move the centrifugal advance).

Retarded timing would cause a power loss. I would spend some time verifying things are working in the distributor.

Sorry I skipped right past you're post Zed Head. So have I verified the operation of the breaker plate by using the mighty vac? It did move clockwise while applying vacuum. What should I expect to see on the timing with it disconnected (what do you mean by off-idle?) and while revving it up?

I am starting to think that there is little else to test other than compression.

[Zed Head]

The vacuum source for the vacuum advance is what they call "ported" vacuum. The port to the hose is closed when the throttle blade is closed and open as soon as the throttle blade comes off of the idle position. So with a timing light, at idle, you might see ten degrees. As soon as you open the throttle a little bit the timing will advance due to the vacuum advance, then as you rev it, the timing will advance even more due to the centrifugal.

If you want to test the vacuum advance completely separately from RPM, connect the hose to manifold vacuum. The timing will jump up as soon as the vacuum is applied and drop back down when the hose is disconnected. Leave the hose disconnected and rev up the engine and you can see how the centrifugal is working.

If you want to get really specific and measure how much of each you're getting, set your static timing to zero (you'll have to bump the idle up to keep the engine running), then measure vacuum as described with direct intake vacuum and centrifugal by RPM (rev until it stops increasing). You have to set static to zero to use the timing scale, unless you have a dial-back timing light. Vacuum is typically about 15-18 degrees extra, and centrifugal about 20, depending on your distributor parts.