My Z is bogging down

[grantf]

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.

Understood, terminology: is centrifugal advance the same as mechanical advance?

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.

Understood I will perform this test tomorrow and report back

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.

I had to reread this twice but I understand. I may dive into testing the distributor more, but could this be barking up the wrong tree or a likely cause of the symptoms?

[Zed Head]

I know that a lack of timing advance will reduce power, but don't know how much is not enough. Personally, I like to know what the numbers are so I have measured both vacuum and centrifugal (mechanical, centripetal... refers to same thing even though maybe not the right word) on mine. If you have the timing light on and rev the engine up until the mark passes the end of the scale, you'll know you have at least 20. You can probably eyeball it up to 30.

Kind of hard to tell since "bog" is a subjective word. One man's bog is another man's hesitation.

Plugged exhaust still seems like a potential cause also.

[madkaw]

I would disconnect the brake booster from the system and anything else vacuum related and see how it runs.

Definitely get your timing figured out.

You need to get the FSM and check all your resistances. Especially the AFM sinceyou messed with the flapper door. That flapper door is tied into a potentiometer, so you if you bent things around you might have changed things. There are tests you can do witth a mulimeter to make sure it is right

Edited June 28, 2012 by madkaw

[grantf]

Zed head, perhaps "bogging down" is vague at best. What I am experiencing is a lack of HP but in a big way. When I drive it I can push the accelerator all the way to the floor and the car will barely reach 3000 RPMs. uphill is even worse. I would say that it does not hesitate, stumble or stall. Idle is steady. Vacuum though low is steady and reads predictably when revving (does not flutter and drops a little with increased rpm then climbs to around 20 hg when throttle is released). It's like I am trying to tow a mac truck. With the car parked, if I rev the engine it revs fine up to about 4000 RPMs then the engine will start to run rough and not climb higher. Before anyone jumps on the clutch or brakes I am sure it is not ether (car coasts just fine and no burning clutch). I still need to perform the tests you mentioned above later this evening and I will report on the results.

Madkaw, You are correct in regards to the AFM, but I am not considering it to be in any way the culprit. The symptom I have existed before I "messed" with the AFM and no change has occurred with performance since then. I calibrated the AFM last year after finding out that the P.O. had adjusted it way rich. I increased my mpg from about 9 to 19 mpg and the fuel cut off restored to normal. I was very gentile with it and it no longer has the sticky spot. I may revisit the AFM at a later date just to fine tune it (I suspect I am running a little lean). As stated above I have disconected the booster and heater control vacuum hose as well as the EGR system hoses and they have not caused a change in vacuum readings.

I am considering cutting out the catalytic converter, but I will not do that until I have ruled out other possibilities.

Thanks again and I will give a little more info this evening.

[grantf]

Ok, so I did some more testing, this is what I found.

The timing at idle, engine up to temp and everything connected is 13 deg advanced

The timing with the vacuum advance routed straight to manifold vacuum at idle resulted in an increase of about 5 deg, total about 18 deg advance.

The timing with vacuum advance disconnected completely and revving the engine to 2000 RPMs resulted in an increase of over 20 deg. Hard to tell really like you said off the scale.

I understand that these numbers are not precise and I did not set my static timing to 0 before timing, but I am getting the idea that even though my vacuum advance seems low perhaps due to low vacuum that my distribution system may not be the culprit. I hate to focus on one idea, but I keep returning to the idea that this may be a clogged exhaust.

Edited June 28, 2012 by grantf

[Zed Head]

The clues do seem to point to exhaust. Seems like a good muffler shop would know what a clogged exhaust system sounds like. The gases don't pulse the same coming out of the pipe. Might be worth having one take a look. Find an honest shop, of course.

The lack of vacuum advance could be due to the lack of intake vacuum, which could be related to a clogged exhaust system.

[280~Master]

I have heard of the Fuel Presure regulator not functioning under a load but will read just fine when idle or reving.

Double check that TPS and its getting good conection.

How old is your fuel filter? To me it sounds like your car is starving for fuel.

Check your filters even the one inside of your fuel tank.

Good Luck

John

[grantf]

I have heard of the Fuel Presure regulator not functioning under a load but will read just fine when idle or reving.

Double check that TPS and its getting good connection.

How old is your fuel filter? To me it sounds like your car is starving for fuel.

Check your filters even the one inside of your fuel tank.

Good Luck

John

You know it's funny you mention the fuel filters and the TPS. The first thing I did after noticing that my car was running poorly was first to replace the after tank filter then the under hood filter. Then I looked at the thermostat because my engine was running a little hot. Behold! the P.O. (idiot) had installed the old one in upside down! never ceases to amaze me what the last owner could screw up on the car. Oh and I did take a look see at the TPS it has not changed since I last adjusted it a year ago.

I have suspected the exhaust to be the culprit from the start, but I have not been sure. I still have not ruled out something else yet, but I am getting a pretty closer to actually thinking that it is the catalytic converter. before putting my EFI back in normal running order last year it was running very rich. So much that I had black soot building up on the rear bumper and left tail lens. I have heard that a rich condition is bad for catalytic converters.

So if it ends up being the exhaust I am thinking of buying an exhaust kit from ether MSA or BD. any thoughts on there exhaust products?

Edited June 29, 2012 by grantf

[grantf]

I cut out the cat and put in a straight pipe today. The core was completely crumbled away and the screen at the back was totally clogged up.

I took the car on a little test drive and the lost power is back, also took a new vacuum reading and it increased by 2 hg. I am not out of the woods yet, I think my manifold gasket is leaking and I am almost sure that I have a small head gasket leak, I saw a little oil bubbling out at the rear near cylinder six. Tomorrow is a compression test and further planing but that is a different story and perhaps a new thread. Thanks for all the help tracking this down I always learn a little more when ever my car gets sick.