90 - Running out of breath at 5000 - No Codes

[scottfab]

SECONDARY PORT THROTTLE VALVE SYSTEM error
But of course you know that.

Try seeing of the actuators pull in
http://www.zr1specialist.com/HAT%20W...0Operation.pdf

If they do maybe your secondary fuel pump is tits up.
You could be running out of fuel but no code is set if it's not
lean enough to trip the code.

[dondon]

Originally Posted by scottfab

SECONDARY PORT THROTTLE VALVE SYSTEM error
But of course you know that.

Try seeing of the actuators pull in
http://www.zr1specialist.com/HAT%20W...0Operation.pdf

If they do maybe your secondary fuel pump is tits up.
You could be running out of fuel but no code is set if it's not
lean enough to trip the code.

Thanks for your help with this problem. I have performed the check by shorting pin C17... unfortunately everything worked as it should, so now to keep checking till I find something.

I don't have equipment to check the fuel pump... so I'll have to take it in sometime this week. Thanks for the input.

[scottfab]

Originally Posted by dondon

Thanks for your help with this problem. I have performed the check by shorting pin C17... unfortunately everything worked as it should, so now to keep checking till I find something.

I don't have equipment to check the fuel pump... so I'll have to take it in sometime this week. Thanks for the input.

Open the hood.
Engine off but ign key on.
Does the vacuum pump under the passenger side head light run?
Does it keep running without shutting off?

[dondon]

Originally Posted by scottfab

Open the hood.
Engine off but ign key on.
Does the vacuum pump under the passenger side head light run?
Does it keep running without shutting off?

It runs for a moment then stops.

FYI - the shorting of C17. While the actuators are moving, the pump runs, then shuts off again. Actuators stay open for as long as I'm patient enough to short the circuit.

[scottfab]

Originally Posted by dondon

It runs for a moment then stops.

FYI - the shorting of C17. While the actuators are moving, the pump runs, then shuts off again. Actuators stay open for as long as I'm patient enough to short the circuit.

Sure sounds like secondaries are fine. Look to fuel pump #2 failure.
The only thing that puzzles me is that I'd expect a lean code to be set.

[Paul Workman]

Originally Posted by dondon

Thanks for your help with this problem. I have performed the check by shorting pin C17... unfortunately everything worked as it should, so now to keep checking till I find something.

I don't have equipment to check the fuel pump... so I'll have to take it in sometime this week. Thanks for the input.

A lot of preliminary stuff can be done at home. (Besides, I don't know 'bout your situation, but there isn't any dealership I'd take an LT5 to for anything!)

As for checking the fuel pumps, all you need is a fuel pressure gauge that you can rent free from AutoZone** and a Volt Ohm Meter from Radio Shack or the like.

You can start by measuring current draw to the pumps. There is a fuel pump test connector jutting out of the same wire loom as the diagnostic connector, located near the top of the power brake booster, next to the firewall.

With the key off, and the VOM configured to read Amperes (most set up to read 10A) put the red lead to the positive terminal of the battery and the black lead to the little red pigtail. Each pump draws between 4-5A. So,if both pumps are running normally, you'll measure between 8 and 10 amperes, you'll hear the pumps running, and with a fuel pressure gauge connected to the Schrader valve, fuel pressure should be about 52 pounds, give or take a pound or so.

Configuring the meter to read amperes...



The red test connector connected (via a yellow jumper with alligator clips on each end - alligator clip leads available from Radio Shack) to the black lead of the meter.



With the red lead connected to the positive post of the battery, the current draw is normally 8-10 amperes if BOTH pumps are running. If only 1/2 that current is present, then one of the pumps is either kaput or there is a connection issue (possibly).



Then you can check the fuel pressure under driving conditions, by taping the pressure gauge to the windshield and monitoring the pressure at normal load and at WOT.



Pressure should be in the mid 40s in normal driving loads, and "pop" up to 52 (give or take) at WOT.

If the fuel pressure is low, especially at WOT, it could mean a problem with a pump, OR the fuel filter. (The filter is next to the frame rail behind the right front tire, and under a heat shield.)

Since the secondaries tested OK, you might want to know what the resistance is across the injectors when they're HOT. They should read between 12-14 ohms (hot). If they read 10 ohms or less, it indicates problems likely. A reading of 8 ohms or less and the injector is definitely in need of replacement; not only to run better, but to prevent the possibility of a burnt valve (ask me how I know...). (The procedure is well laid out in the FSM.)

And, of course, the easy thing to do is change plugs.

[scottfab]

absolutely phenomenal wright up Clear easy to understand and easy to read

Originally Posted by Paul Workman

A lot of preliminary stuff can be done at home. (Besides, I don't know 'bout your situation, but there isn't any dealership I'd take an LT5 to for anything!)

As for checking the fuel pumps, all you need is a fuel pressure gauge that you can rent free from AutoZone** and a Volt Ohm Meter from Radio Shack or the like.

You can start by measuring current draw to the pumps. There is a fuel pump test connector jutting out of the same wire loom as the diagnostic connector, located near the top of the power brake booster, next to the firewall.

With the key off, and the VOM configured to read Amperes (most set up to read 10A) put the red lead to the positive terminal of the battery and the black lead to the little red pigtail. Each pump draws between 4-5A. So,if both pumps are running normally, you'll measure between 8 and 10 amperes, you'll hear the pumps running, and with a fuel pressure gauge connected to the Schrader valve, fuel pressure should be about 52 pounds, give or take a pound or so.

Configuring the meter to read amperes...



The red test connector connected (via a yellow jumper with alligator clips on each end - alligator clip leads available from Radio Shack) to the black lead of the meter.



With the red lead connected to the positive post of the battery, the current draw is normally 8-10 amperes if BOTH pumps are running. If only 1/2 that current is present, then one of the pumps is either kaput or there is a connection issue (possibly).



Then you can check the fuel pressure under driving conditions, by taping the pressure gauge to the windshield and monitoring the pressure at normal load and at WOT.



Pressure should be in the mid 40s in normal driving loads, and "pop" up to 52 (give or take) at WOT.

If the fuel pressure is low, especially at WOT, it could mean a problem with a pump, OR the fuel filter. (The filter is next to the frame rail behind the right front tire, and under a heat shield.)

Since the secondaries tested OK, you might want to know what the resistance is across the injectors when they're HOT. They should read between 12-14 ohms (hot). If they read 10 ohms or less, it indicates problems likely. A reading of 8 ohms or less and the injector is definitely in need of replacement; not only to run better, but to prevent the possibility of a burnt valve (ask me how I know...). (The procedure is well laid out in the FSM.)

And, of course, the easy thing to do is change plugs.

[dondon]

Scott and Paul, thanks for the help. I've done some testing...

The good:
Bought a fuel pressure guage, hooked it up.
46 PSI when can is not on, 41 PSI when car has been started and was running. FSM and precious comments in this thread indicate 48 - 55 PSI before start up as the correct measurement. So its a bit low. As you know this doesn't necessarily test the secondary pump, unfortunately I couldn't find and extension pipe.

The Bad:
I couldn't get a reading on my Multimeter (testing red pig tail, on mine it appeared orange and black... not sure if I had the right one, but the location was identical). probably doing something wrong.

Next steps:
With the pressure being low, I'm going to buy a new fuel filter, and 2 pumps. Hopefully in a week I can report back and say its happy days. Its going to be a big week for the little Z, it should have new shoes arriving this week.

Thanks again for all the help, if the plan of action doesn't make sense please let me know.

As for dealers... I've found a locally owned not Chevrolet dealership that keeps me quite satisfied, prices aren't that dissimilar to a dealership, but I trust them and that's more important to me.

[Paul Workman]

Originally Posted by dondon

As for dealers... I've found a locally owned not Chevrolet dealership that keeps me quite satisfied, prices aren't that dissimilar to a dealership, but I trust them and that's more important to me.

You know best, but these cars are older than a lot of people working at some shops, and most(?) have never seen an LT5 before. These pages are filled with horror stories. Just sayin. SGC is Georgia, if that helps.

As for the high pressure reading, depending on whether there is perhaps air in the fuel line, the pressure may not peg at the 55# due to the secondary pump is shut off in a couple seconds. With the ignition switch OFF, connect the positive terminal of the battery to the red test connector on the wire loom and see what your fuel pressure is then. After a couple seconds, with both pumps running, the pressure should be in the 52-55# range. If it is, then the pumps are running.

However, see if you can find an extension (got mine at AutoZone too) to observe dynamic fuel pressure. Only then you will know if the system will provide fuel at the rate required at WOT. If, for example, the fuel filter is choked up, the pressure will drop across the filter, indicating the pumps are probably OK, but there is a flow issue.

Change the pumps if you want. But, I hate to see you changing parts in place of troubleshooting. That is how unforeseen variables get introduced to the initial issue, e.g., infant mortality, is the term applied to new parts that failed "out of the box".

Good luck!

P.

[scottfab]

41psi is not low. It's way low.
Yes fuel filter on GP first if you're not sure how long it's
been but note likely the issue.
You're sitting right on the problem I'd say.
One or both fuel pumps. If you get 41 at about idle
imagine how it may drop off under high demand.
Best investment would be an extension and some tape.
Seems prudent before proceeding.

A note about the pig tail. It's the only one at that
location so unless someone added something you've got it.
It ONLY works as a test when the key is off. It does nothing
with key on because the way it is routed through the relays.
ALSO important to note with key off and applying 12v to the
pig tail you get BOTH pumps running. It's a great static test.
From there you can remove one or the other of the fuel pump
fuses to see what pressure each pump can do. You do not want run
these pumps for long periods of time through the pig tail. Just saying.... do each test, not the pressure and shut it off.

As for a place to work on your car. YOU will be the best influence
on how well they do with the car but you have to study up here
on the forum and show them the results.