Vacuum pump not coming on?

[1963korvette]

Bought car 3 months ago. It has been running very rough. Idle seems high at about 2000 rpm's. bogs down thru 3000 to 5000 rpm's. Tested the vacuum pump testerday. Turned on ignition key and did not hear pump come on. Don't know where to go from here. Appreciate any help or ideas.

[QB93Z]

You have done valuable troubleshooting already. 2000 rpm idle probably means an air leak in one of the vacuum lines attached to the plenum.

The bogging in the 3000 to 5000 rpm may be due to the seconday system being commanded on and then commanded off again when the vacuum switch senses that the secondaries did not open.

Try running the car with the Power Key off. If the bogging down goes away you have confirmed that problem is the secondaries.

My 1994 ZR-1 had similar problems after I bought it last May. The vacuum pump was seized and rusted, probably from running all the time trying to keep up with a vacuum leak. In my case it was a failed check valve in the secondary vacuum system.

You may have a disconnected vacuum line, 2000 rpm idle is a large air source to the plenum.

Check the Manifold Air Pressure Sensor (back of the plenum) hose and make sure it is connected to the plenum. It is under the MAP sensor.

It is possible to test the vacuum pump using jumper wires from a 12 volt source connected to the terminals, but I would guess 95% probability that the pump is bad. I haven't checked on the availability of the 1990 style vacuum pumps lately but there have been some recent posts about replacing the pump using the later model pump by changing the connector.

Have you ever pulled the plenum on an LT5?

If you need help, I might be able to find someone near you that can assist.

TomTom are you listening?

Good luck,

Jim

[secondchance]

You have done valuable troubleshooting already. 2000 rpm idle probably means an air leak in one of the vacuum lines attached to the plenum.

The bogging in the 3000 to 5000 rpm may be due to the seconday system being commanded on and then commanded off again when the vacuum switch senses that the secondaries did not open.

Try running the car with the Power Key off. If the bogging down goes away you have confirmed that problem is the secondaries.

My 1994 ZR-1 had similar problems after I bought it last May. The vacuum pump was seized and rusted, probably from running all the time trying to keep up with a vacuum leak. In my case it was a failed check valve in the secondary vacuum system.

You may have a disconnected vacuum line, 2000 rpm idle is a large air source to the plenum.

Check the Manifold Air Pressure Sensor (back of the plenum) hose and make sure it is connected to the plenum. It is under the MAP sensor.

It is possible to test the vacuum pump using jumper wires from a 12 volt source connected to the terminals, but I would guess 95% probability that the pump is bad. I haven't checked on the availability of the 1990 style vacuum pumps lately but there have been some recent posts about replacing the pump using the later model pump by changing the connector.

Have you ever pulled the plenum on an LT5?

If you need help, I might be able to find someone near you that can assist.

TomTom are you listening?

Good luck,

Jim

Well said!
Only exception possibly is my personal experience with blown vacuum to MAP resulted in the motor huffing and puffing and barely could hold idle.:mrgreen:

[tccrab]

First things first, find the vacuum leak.
You've got a big one.
The vacuum pump only assists the secondary system when the engine is at high rpms for an extended time.
Don't worry about him right now, but know that you'll have to come back to him later.
First thing is to check the MAP sensor hose.
It's behind the plenum on the drivers side.
Use a flashlight and look for a pipe that is disconnected.
It's a common thing, this hose pops off when the engine backfires during a startup when the key is not held in the start position until the engine is running.
The LT5 takes longer to start than a regular Chevy engine for a couple of reasons, but primarily it's because there's no distributor. All the sensors have to polled by the ECM before the actual signal to fire the coils is sent.

Here's all you need to know about your secondary system:
http://www.corvetteactioncenter.com/forums/c4-corvette-zr-1/14272-1990-1995-zr-1-secondary-port-vacuum-diagnosis.html

After you get your leak fixed, then it's time to work on the vacuum pump.
Let us know when you get there. There are a few options.

TomC
"Crabs"

[1963korvette]

Thanks for the replys guys. When I first noticed the bogging it seemed to be only with full power. However, now it feels the same either way.

[tomtom72]

:hello::happy1: Reporting as ordered, Sir!

Have tools & will travel........Road Trip! NJ, what exit??? Now I really have to go get another EZ-pass module for the Z!

'63 PM me if you need help. Or thomastom72@aol.com is my e-mail addy. I have a scanner & software for a 90, plus a ton of spare parts. :mrgreen:

As others have said, vacuum leak(s) will give an alternate air route to cause a higher idle. Or, the MAP hose is blown off, I'd check that first as it's the easiest thing to check. If MAP is okay, then start looking at all the vacuum lines after plugging the hose from the pump that goes under the plenum. You could throw a mity-vac pump on that one to check if the under plenum stuff is okay. Also, on a 90, the fuse for the pump is over on the driver's side bolted to the rear inner wheel house panel. It's a small rectangle usually near the s/s brake lines. That fuse could be blown, probe the connector @ the pump for 12v w/KOEO & see what's up.

Bogging, does it knock when bogging? Could be a lean bog, bad injectors or a big vac leak? At idle, no missing, right? You checked for good spark? Condition of the plugs, PCV's, Fuel filter are all okay? Or, do you mean "it's breaking up" or "chugging" when you put your foot into it? Bad MAP or disconned MAP hose.

:cheers:
Tom

I will check my software to see what yrs are covered, I have a 90 so that's where I stopped reading.

[1963korvette]

Wow that a lot of questions. Will check out all these possible problems when i get home tonight. The best way to discribe the bog is it feels like its getting to rich a mixture and engine is flooding. If I need help I just might take you up on offer to come on down. 30 sec. off parkway exit 166.
Thanks
Rich

[tomtom72]

Hi Rich & welcome to the Brotherhood! :handshak:

Okay, not a problem....we're like that in this group. I have software to 93 on primary cartridges and a troubleshooter up to 92 for my scanner.

I would say that from your further description to check that MAP hose. Also, check to see that hose is not full of oil, that happens alot and it can cause the MAP to not get the vacuum input as it clogs the MAP over time. Can you smell it at idle if you give a sniff at the tail pipes? At speed can you smell it in the car?

:happy1::cheers:

[1963korvette]

Ok, here we go. Got home last night, unfortunately it was dark, the 63 hogs the garage. Inspected the engine for any loose hoses and wouldn't you know found one. It sits behind the engine just under the pellum behind the distributor about a 3/8 inside dia. hose about 8 inches long. But whats puzzling is what it looks to go to I would have to bend it like a pretzil to get it on. The piece it seems to go to has two nipples coming out, obviously one is open. Started engine and could have vacummed my house with it. When I put finger over the hose my idile dropped down immediately. Have attached photo of where it comes from to kinda where it goes.

thanks

[tomtom72]

I have to get me some of that Ginko stuff, forgot to add that I have a spare vacuum pump in my parts inventory....:o....justthat it's the one from the truck catalog and we will have to adapt the wiring at the connector. I may also be able to restore your pump. I did mine. It took some time and some solder and contact cleaner...a lot of busy work, but they are repairable.

:cheers:
Tom

Okay I looked & that is the PCV system. We have two valves. As long as the rubber is intact and the PCV's rattle when you shake them, then you should be okay. If you find any suspect rubber parts let me know as I have a good inventory of all that stuff!

[QB93Z]

Good job finding the vacuum leak.

Here is a picture of the major parts of the Positive Crankcase Ventilation system:

http://i407.photobucket.com/albums/pp152/QB93Z/Misc/DSC02906.jpg

Are you missing any of these pieces? On some cars, the rubber gets soft and these pieces don't stay connected. You may need to put some zip ties around the parts to hold them.

Jim

[1963korvette]

Couldn't get pic of where they connect. but the left side comes to the back of engine and t's off with one end going down on to the valve and the other end is the loose one. The right side goes down under to who knows where couldn't see what it connects to. Sorry can't give better description.

[1963korvette]

Now that I think about it. I don't believe that that top piece in photo is on the motor does that connect left side to both valves? I have a plastic T.

[QB93Z]

The two metal PCV valves plug into the two sockets in the long rubber hose. The smaller rubber piece plugs on to the top of the two PCV valves. The whole assembly is installed behind the plenum. The longer rubber piece connects to the left and right sides of the engine through metal tubing and then a right angle rubber fitting into the Injector Housings, (the left hand arrow in your pic.)

The top rubber piece connects to metal tubing (the right arrow in your pic) that runs along the driver's side of the plenum and connects to a rubber fitting under the front of the plenum.

You will meed four small hose clamps to securely connect the four openings for the long, lower rubber piece (one on each end, one on each PCV valve).

Good Luck.

Jim

[1963korvette]

Ok. Jury rigged PVC connections til I order new rubber parts. Idle went down to 1400. Looked for other air leaks could not hear or see any. Went for ride and it acted like it was going to stall out. Ran very rough and sounds like a diesel engine. The battery doesn't seem to hold a charge, going to replace next week. Any thoughs.

Rich

[tccrab]

Rich:

ZR1's are very fussy about battery strength.
If the battery drops much below 12v all kinds of gremlins can jump out and bite you.
Getting a new battery is a must if yours is having charging issues.

Your idle is getting better, sounds like you've still got vacuum leaks.
It should normally idle at 850.
On my '90 I chased a vacuum leak for ages that was causing idle issues.
Turned out to be a vacuum connector just behind and under the throttle cables. It's hard to mess with because it's tucked underneath there and if it's not exactly right the damn thing leaks like a sieve.
It's a '90 model year only connector, GM realized it was not a brilliant design so they changed it in '91.
I was able to buy a new one from JeffVette (a.k.a. Jeff Flint) here on the forum. He has the worlds only supply of spares. After replacing mine, I decided if it ever gave me problems again that I'd re-engineer the connection and get rid of the #@!#$%%ing thing.

Idle aside, the running rough could mean many things. Fuel injectors, coils, wires, plugs all come to mind.

I'd highly recommend that someone familiar with these engines pay you a visit for a little diagnosis assistance.
Nothing is cheap for these cars, and I'd hate for you to just throw buckets of money at the car unless you had to.

Do you have a FSM (factory service manual) for this car?
It's an absolute necessity if you're going to work on this car yourself.
If not, here's a link:
http://www.helminc.com/helm/product2.asp?class_2=CHV&mk=Chevrolet+%26+Geo&yr=1990&md=Corvette&dt=&module=&from=result&Style=&Sku=ST36490LT5K&itemtype=K&mscsid=RJ5SSWW1FT608KPJ9JX5WR6BV30U2TQ1

TomC
"Crabs"

[tomtom72]

Rich,

Not to beat a dead horse, but did you locate the MAP sensor vacuum line at the rear of the plenum and check to see it is still on the plenum port and not filled with oil?

Sorry, not trying to be a wise guy...:o It is important that the MAP is getting a vacuum signal. That hose is the first casualty if the motor backfires at start up. It can also get loose with age and come off very easily if you were poking around back there...like working on the bottom PCV hose.

I'll PM you my digits just in case you need moral support!:mrgreen:

:cheers:
Tom

[1963korvette]

No I did not locate the map sensor yet. I did not really look for it yet. I was so happy just to find the PVC laek I forgot to look for that. I will look tonight.
Thanks

[QB93Z]

Just for reference, here is a picture showing the location of the MAP Sensor. This is a 1993 LT5, and there are some differences from your 1990, but the MAP is the same.

http://i407.photobucket.com/albums/pp152/QB93Z/Misc/JimsLT5-1withMAPlabeled2.jpg

If the MAP hose is softened, it will collapse under high vacuum in the plenum. High vacuum occurs at idle and low throttle operation.

Good luck,

Jim

[Jeffvette]

Just for reference, here is a picture showing the location of the MAP Sensor and hose. This is a 1993 LT5, and there are some differences from your 1990, but the MAP is the same.



Jim, the hose you are pointing is the Fuel Pressure Regulator Hose.

Map sensor hose can't be seen from the top or side. Need to reach down and feel it.

[QB93Z]

Jim, the hose you are pointing is the Fuel Pressure Regulator Hose.

Map sensor hose can't be seen from the top or side. Need to reach down and feel it.

Thanks Jeff. I was relying on memory and obviously, I was confused.

I edited the photo and removed the confusing label.

Jim

[Jeffvette]

Thanks Jeff. I was relying on memory and obviously, I was confused.

I edited the photo and removed the confusing label.

Jim


No worries. The fuel pressure hose is basically the same construction. Rubber ends with a plastic tube.

[1963korvette]

Think I found the source of the leak. PVC hose the larger hose had elctrical tape on it. When I pull it out it had a hugh tear. Ordered new setup from White Racing. Then pulled out the Vaccum Pump opened it up and there seems to be some corrosion not alot. How do I check it, would touching the terminal to a car battery work?
Thanks

[tomtom72]

Yes Rich, just fab up a two wire connection and use the battery. I had corrosion in my pump. I used WD40, some pencil erasers and a small brass brush and some contact cleaner to get rid of the WD40 as a last step.

:cheers:
Tom

[QB93Z]

The best test is to have the vacuum pump installed in the car and turn the ignition key to ON but don't start the engine. The vacuum pump should run for a few seconds and then shut off. You can hear it from the driver's seat, but if you have a doubt, have someone turn the key while you listen close to the pump. If the pump runs continuously or starts and stops periodically, then you have a vacuum leak in the secondary vacuum system. If the vacuum pump but doesn't make any sound, then it is faulty or you have an electrical problem.

Jim

[Hammer]

Vacuum pump from a Kodiak truck. Bolts on to a 91-95 ZR-1, but a harness adapter is available (according to Marc) or you could make one for a 1990.

https://www.partszoneonline.com/parts.php?srch1=94669091&srch2=&srch3=&srch4=&srch5=

Original Pump part No. 15198448
Kodiak part No. 94669091

[cward]

The vacuum pump only assists the secondary system when the engine is at high rpms for an extended time.

TomC
"Crabs"

I am late getting this on but I was told by Graham B many years ago that the Yanks made them put in the vacuum pump for the very specific reason mentioned by Crabs. I did not have a vacuum pump on #364 and it ran just fine even at high rpms for an extended time. That said, I know that most Z owners will want the pump anyway. Just thought I would mention this in case you did not want to spend the money.

Curtis

[1963korvette]

Ok, fixed vacuum pump. When car warms up idle is about 1400 rpm, then every 20 sec drops down to about 800 rpms and it sounds like you are shaking a can with rocks in it. Can't see any other leaks I assume will have to pull pellum, but want to find out what I will be replacing first. Any thoughts?

[tomtom72]

Hummmm.....that's a new one. Okay Rich, so I make sure I get what you're saying: idle fluctuates between 1,400 & 800 on an almost even time frame?

Sounds like a fueling issue to me, or at least that's where I'd begin. In my mind, god that's a scary thought!.....the ECM is adjusting the pulse width to match O2 readings that are out of the expected "normal". That takes a bit of time to see the results of the ECM's changes if the injectors are at fault.

The rocks in a can noise is the dual mass flywheel reacting to the variations in force ( fuel ) in the suspect cylinders(s). It's kind of like a subliminal miss. It could be the injectors are going out to lunch. A scan to see the Block Learn numbers and the integrator numbers and the O2 numbers would seal the deal if there is a fueling issue. Those numbers are key to let us "see" what the injectors are doing in response to ECM commands, which are a reaction to what the ECM is seeing from the O2 sensors. The reason I say scan is that you said warmed up it does this stuff. Usually when theearly injectors have coil failure it shows up after the car is warmed up and gets worse the hotter the injector coil gets. You can do an OHM test thru the ECM harness plugs for the injector coils, that can also help in the diagnosis in the absence of a scanner.

If you stand behind the exhaust pipes can you smell anything? Rich or Lean smell? If you listen at the pipes do you hear any rich gurgling or lean pops?

Can you get a scanner with the right software to borrow? Do you want me to swing by & bring my stuff?

:cheers:
Tom

[tomtom72]

I need some help from the brain trust in my effort to help out Rich with his 90 Z.

I scanned the motor last night and got no DTC's, almost everything looked normal when compared to our "reference" page in section 6E with the data snap shot.

The car has a miss, or so it seems or like it's stumbling, but when you get into the secondaries past about the tip in point it runs fine, no stumble.

Here are some of the scan data in closed loop @ idle that I thought was not too great, and by the book it appears not to be too good either when I looked it up.

Block Learn enable = YES. book says it should be NO.

BLM cell = 16 ???? book says it should be 0 - 1.

Left BLM - 127 to 128
Right BLM - 136

Left Integrator counts were from 127 thru 133
Right Integrator counts were 126 thru 131

MAP reading in volts was 1.5 volts which is out of the book range of 6v to 2v.

I told Rich that knowing that the Air & fuel filters, plugs & wires & PCV's are new, to check the plugs for color, check that the spark is good. I'm not too sure about me laying blame for the stumble on the primary injectors.

Oh yea, his tach is about 1k rpms fast, how do you fix that?

TIA
:cheers:
Tom