I've got many issues with my baby:

Question #1) My '84 Z28, L69 5.0 is fun to drive, but when an in-law drove my car he said that my car should be A LOT faster than it is right now. My exhaust system is the original 20+ year old exhaust, except the muffler, and this car spent its entire life in the salt belt. Could the source of my power loss be a backed up cat??? When comparing acceleration to my wife's 2.0 4cylinder car the difference is noticible. While my car is fun to drive the power isn't there.

Question #2) Also, my ECM pigtail (near battery) was unplugged. So I connected it. Now my idle is 2200 cold, 1750 when warm, and 1150 when in drive?

Question #3) Also, I noticed the hose going to the MAP sensor is disconnected. Help???

Question #4) Also, my am I only getting about 8-10 mpg and I have a light foot. Is this from any of the above?

 

1. Yes the CAT is probably clogged, at least when mine was clogged I had a big loss of power.
2. ?
3. ?
4. A bad O2 sensor will cause poor gas milage.

Hope this helps.

 

I know the cars' computer doesn't do much when it comes to running (in general), but with regards to my idle problem, do I need to reset my timing (give the distributor a whirl) to a baseline with the ECM connected?

 

Sounds like someone set the timing with the "ecm pigtail" unplugged. Thats why it idles high when plugged in. IIRC it'll jump some 10-12* between unplugged and plugged in. Clogged cat? Doubtful. You'd smell an awful foul rotten egg smell.

Replace Oxygen sensor, Reset timing to whatever the prescribed base timing was for your year with the pigtail unplugged, check your Carb/TBI to make sure that idle set screws are or whatever they are, are going to make the car idle at a more respectable level.

If your distributor is an electronic advance, and the pigtail is unplugged, you are getting no advance.

 

The car is all original, running the Q-Jet carb and factory Distributor.

I would prefer to use the computer. I guess that it would make sense that the computer just added timing to the unplugged set timing. Not a very smart computer.

All my vacuum hoses are connected (all are new). All my emissions stuff is plugged up. However I noticed that on the passenger side exhaust manifold there is a rusted device that is stuck either open or closed, and it has an open air line without any attachments, and I haven't found anything else available to be plugged into it ... maybe something for the EGR? It is amazing this car runs and drives.

 

Gary,
If the carb was unplugged then your primary metering rods would have been stuck open making it run rich. Not only that, but the timing is controlled by that computer, so something like twenty degrees of advance would be missing at cruise. Twenty degrees equates to probably fifty horsepower. No wonder it was a dog!

Firstly, plug in the computer.
Secondly, Find the large five-wire flat connector that connects the distributor to the harness and disconnect it. Now start the car, and set your base timing with a timing light to eight ot ten degrees BTDC.
Reconnect the distributor and let the engine warm up. Now, Make sure that the carb is no longer on the fast idle cam. Since you can see the linkage, make sure that the electronic choke pulloff has indeed pulled the choke wide open. If the engine is still idling high, next check to make sure that the idle kicker solenoid hasn't been adjusted to hold open the throttle blades.
After that, adjust the throttle stop manually to get a decent idle.

Now, that MAP sensor on the cowl is not a MAP sensor but a BARO sensor. It is in essence a barometric pressure sensor. It is supposed to be open to the atmosphere. There isnt any MAP on this particular car.

You may have additional vacuum leaks as there are vacuum lines all over the place on that engine. Look for any vacuum lines that may have turned into black goo and replace them. Make sure you have a good EGR hose and a good PCV valve. Oh yeah, that reminds me: Your EGR could be stuck open. Pull it off and push on the diaphragm to see if it still moves. It might be carbon choked, and this will make your engine run quite badly. Clean it up and reinstall.

If you have been running rich for a long time there is a good chance that you have burned out the monolithic block on the inside of the catylitic converter. They will literally melt, and sometimes vaporize. However you wont have much way to tell. Mine was stil good at 133,000 miles, actually, which was about when I converted to a big cam. Then, when running really rich, I destroyed an aftermarket high-flow cat in 5000 miles. So, with only 10 MPG you probably have damaged that catylitic converter. You wont really know except by removing it to have a look. Unfortunately your converter , which was a high-flow oval style from the Corvette program, has probably been permenantly rusted in place on its four-bolt flanges. That was one of the reasons why I converted to a three-inch slip fit style cat.

So, assume it's dead, and plan accordingly when you build a new exhaust system. By the way, my exhaust lasted a good fifteen years, too! GM had some really good pipes on those H.O. equipped cars, didnt they??

In the mean time, check those things I mentioned above and let me know what you find.

 

Thanks ... you are the man!!!

I'll let you know what I find out.

 

you didnt address his heat riser valve.thats th epart you spoke of on the passenger side exhaust manifold,these burn out all the tiem and stick close alot,restricting that side of exhaust huge.there should be a vacuum line running from it to the tvs on the front of the intake manifold.also on the valve itself there should be a diaphram,with a rod,thats what actually opens and closes the valve,see if that moves freely and take a vacuum pump to it and see if it will open.if not replace with a new one or get a spacer and just remove it entirely and fre up your exhaust some.also if you remove it make sure you plug up the vacuum line which fed it.as a matter of fact find that line anyways cause if its not hooked up like u said you got a leak right there

 

also ,not to knock your car at all,but even in its day i thinkit was only rated at 190 hp,ok for its time but for todays standards low end and dont be suprised how many suvs.4 and 6 cylinders will walk away from that car these days.even new it was a 16 second quarter milers.suvs are faster than that now

 

Thanks. Yeah, the device (as a whole) is 100% rusted (inside and out). The rod assembly is fused with its shell. You mentioned plugging it up. How important is it to the A.I.R. system to keep this thing (with my luck it is critical)?

Right now there is a strong exhaust odor that is coming from either that, the swiss cheese intermediate pipe, the driver side stove pipe that goes into my intake (I sometimes run the air filter cover/top upside down to get more air into the intake), or all of the above.

 

You can safely disconnect and plug up the vacuum line to the heat riser, especially if its nonfunctional. Just make sure it's rusted in the OPEN position and not the CLOSED position. However the heat riser will become a thing of the past if you get the headers and new Y-pipe. It sounds like you need a whole exhaust.

Tell you what: I'm about to pull out my Edelbrock TES headers and put in some Hooker long tube headers. I could probably sell the set with Y-pipe at a fair price if you want. They have the AIR tubes cut off though. Nice thing about them is that I ported the inside of the flanges and they are proven to flow enough air to push a car to a 115 MPH quarter mile. Some surface rust, but not much. You'll need to convert to a slip-fit catylitic converter though, like the 1991/1992 single-cat F-cars.

 

Okay, I didn't remove the EGR valve yet, but I did depress the diaphram. It requires a good amount of force to move it 1/4" to 1/2". I will remove and clean it later this week.

My timing indicator is missing. I already called around, and I can pick one up for $7 at Autozone. After I get that I will reset the timing.

On the Baro sensor ... I have a three wire harness and a port(?) for a hose to plug into it. The hose appears to have a metal connector inside ... like a spark plug wire, and the metal connector appears to have broken off a piece in the sensor.

The heat riser lever is stuck with the lever pulled towards the rear of the car.

 

disconnect egr valve.it wont matter to computer since its only and output signal.computer wont know if its operating,only emissions will tell.
get a set of headers and just remove that damn heat riser all together.if you buy headers get tpi headers w or w/o air tubes.your call..but dont get carb headers since the y pipe connection will be made to mount the heat riser valve.btw tpi headers need a new y pipe for this reason.grab that guys edelbrocks,great for your use and while your at it grab a 50 dollar catco 3 inch cat.
as far as heat riser right now,hard to say if its opened or closed,but there should a diaphram canister on it.basically to open the valve the diaphram pulls the rod and opens it,so if the rod s in the retracted position,clocest to the diaphram,its open,if not its closed

 

I was going to rebuild the carb, but my wife's stepdad checked it out (spends his weekends working in a racing pit) and he said "it ain't broke, so don't fix it."

We did replace the timing chain a couple of years ago (a buddy of mine) ... there was over an inch of play in the chain ... our fish story is the loose chain added about 26 degrees of timing. That is why I am so dumb founded that the timing indicator is now missing ... I guess it rusted itself to freedom.

The first thing I did when I bought the car was replace all coolant and vacuum hose, plugs, wires, cap, rotor, radiator, tires, air filter, PCV, vapor canister filter, fuel filter, radiator cap, oil, PW steering pressure switch, battery, alternator, RADIO, brake lines (the ones rusted through), etc. etc. etc. I've done a lot of minor work to this car ... and rebuilt the trans. Now the rust is messing with my mechanicals and exhaust.

 

Gary, I probably have a spare BARO sensor laying around here among other things. I notice from the pictures that you have the original Packard wires on that car. You might want a new set of wires. I happen to have a spare set of MSDs laying around on a fairly new cap with a good Accel Supercoil inside as well.

I'm pulling the exhaust off probably this weekend so PM me. My outgoing email service is temporarily broken as you could tell. I had a SNAFU with switching domain hosting services and I'm trying to work it out.