bhamvett

Before you guys flame me,I know I said I was going to take some time
off of the forum and I am,but this just came up yesterday evening and
I want to solve this problem this weekend.
I was going to take the car in for repair when it hit me to check the
vacuum line connections "one more time".What I found was that the
vacuum line connection at the very rear of the plenum(the one under the
little metal plate)is not making a good connection,or I should say is not
sealing.The rubber end piece has come off on the bigger rubber line and
the smaller vacuum line does not seal inside the bigger line.It is constantly
"moving" inside the bigger line,thus not totally sealing and sucking air
in where the seal has broken off.I tried a quick fix by rapping the connection
with electrical tape and drove the car and it definately drove better.It
only hesitated ever so slightly only 2 times and it was almost un-noticeable.
My question is thus-can I just buy that one vacuum connection and does
this sound like this could cause my problem? The problem is the space
where the vacuum line lies is so tight you can't get your hand in there good
to address the problem.
Thank's
Steve
The vacuum line I am referring to is the one on the very rear of engine
under the little metal plate.



[Modified by bhamvett, 8:36 AM 6/13/2003]

Aaron71771

MAP sensor line. A loose connection there can cause all sort of little problems. If the rubber/plastic lines and elbow are in good shape, you could probably use a small plastic tie to tighten up the connections. You may want to think about removing the MAP sensor to get to everything. Just be careful not to drop anyting into the great abyss.

baddmann

If you look at my post in your other thread on this I suggested you get the vacuum lines checked out by a local ZR1 certified chevy dealership... They will pull the plenum and replaced the parts. Should be about $100-$150. If you can turn a wrench yourself, it would be less expensive.

91mongoose

You can replace that hose with a small piece of regular vacuum hose. I don't know why GM went with the multi-part hose - it's just more opportunities for a vacuum leak.

If you remove the map sensor bracket to get access be really careful with the screws. If you drop one if them it will end up under the starter (most likely) If you drop the sensor it will fall a little way but the wiring connector will keep it from getting too far; you can fish it out by the wiring. The screws are torx T30s...

ZR1 Jim

My MAP sensor hose blew off once and the car ran like total crap. It would only idle for a few seconds and then stall. I thought I was totally screwed, as this happened when I had only owned the car for a month or so. I really thought I had blown the engine or something. I bought a little piece of rubber hose and replaced the stretched out factory piece. It has worked just fine for almost 5 years now. I repalced it myself without removing any parts, but I have really agile and strong fingers due to my occupation(I am a jeweler).

bhamvett

Thank's for the replies.So you guys are saying that is the MAP sensor
that is under that metal plate that looks like a little black rectangular box.
It as a fairy good sized hose going into the bottom of it.Can I just remove
that hose and then take that box off?I took the 2 torx screws off to
remove the metal plate and noticed it also held that black box in place.
As you all well know the hose I am talking about is under that black box.
I was unsure if I could disconnect the hose to the black box and take it
off,it would have made getting to the vacuum line much easier.
Thank's again,
Steve

91mongoose

The black box is the MAP sensor. Don't remove it from the bracket, just remove the bracket from the plenum (with the map sensor still attached to the bracket).

And BTW - I replaced mine w/o removing any parts as well. But I had seen those parts removed before so I had a better idea of what I was feeling for doing it blind.


[Modified by 91mongoose, 10:11 AM 6/13/2003]

bhamvett

Here is the line I am referring to.It is the line that goes into this spot
on the plenum.It is a two piece line.

A26B

Another bit of advice generated by my own experiences. Not all vacuum hose is created equal. Some hose is more succeptable to kinking than others and if the hose is too long or too thin, it will kink and prevent plenum pressure from being sensed by the MAP sensor. Considering the exposure to oil, I strongly recommend you do not buy vacuum hose. Instead, go to Autozone and buy a short piece of 1/4" fuel hose. It is far more resistant to oil, not nearly as prone to kinking and collapsing and will fit and stay tighter on the connections.

Like everyone said, just remove the two torx bolts holding the MAP sensor aluminum mount to the back of the plenum and you will have all the access you need to replace the line. Jut eliminate all the tubing elbows and go with one piece of fuel hose, cut to the proper length. This will provide a long term fix.

Good Luck.

bhamvett

A26B,
I want to thank you and everyone that helped me.I think(hope) this
was my problem and I will fix it tonight.
I know some of my ranting and raving about certain things get a little
old and I appreciate you ZR1 guys not turning your back on me and
helping me out.We have a great family of people here.
Thank's
Steve
:cheers:

LowFlight

This was the only problem with mine when I got it and the dealer fixed it in a few hours for $40 labor and $25 in parts..not serious at all and common... :thumbs:

cvette

If I were you I would be checking the rest of the vacuum lines before I headed to Nashville. If that one has loosned up there's a good chance you'll find another. I think the vacuum line kit cost me less than $30 from my source at GM. If you need the part #'s and or my source let me know.
Charlie

90 Corvette ZR-1

I've done that :( I had the same problem with my car in BG. Accept that mine blew off.

DDSLT5

Yep - map sensor can cause some havoc - mine was a thick walled tubing that blew off a couple of times - when it came back from LPE it was a smaller line with thick rubber elbows - alot tighter too. Also, once you have MAP sensor off (yes, just remove the bracket and the sensor comes too) check to make sure no oil has made its way into the sensor - this will cause erradic readings as well!! Sounds like you may have found the problem - congrats - NOW DON'T SELL THE FRIGGIN' CAR!! Okay, got that out of my system - it is quite a nice looking car - hate to see you sell it and regret it! :seeya

The Saint

Chris@VetteFinders

purchased my 1990 ZR1 back in January and have been battling a hesitation problem since then. I was finally able to solve the problem. (Note: I had the plenum and injector housings ported in the interim, but the hesitation did not change at all). I spent hours and hours going through ZR1 net archives, forums, the service manual diagnostic charts and even replacing a few "may as well try it" parts. In my search for the cure, I found that this is a very common problem, especially among 90-92 ZR-1s. I hope my information may help someone else out. If you are pulling the plenum, I suggest you go ahead and try this fix.

The symptoms were as follows.

When I accelerated mildly between 2,000 and 3,500 rpm, after about 1-2 seconds with my foot on the pedal, the car hesitates badly. Just for a split second, like it is either momentarily rich or lean. It only does it with the power key on (secondary system activated). With an aftermarket chip in, the problem is MUCH more pronounced. So much so, that you can feel the backlash in the drivetrain. With the stock chip, it was fairly mild. If I accelerated very slowly, it would not do it. If I punch it, pressing the throttle immediately to the floor it would not do it (at least I could not notice it). When revving the engine in neutral, no evidence of a problem. Power through the rpm range was as it should be.

The first thing I tried was removing the plenum and seeing if the actuators were installed "backwards". As you all know, the jury is still out on which is the "right way". Mine were "backwards". I switched them around and found no change. Next I grabbed the service manual and went through the charts.

Tested the injector resistance with them in place. All good.
replaced fuel filter
Injectors sent to cruzin performance. They tested within parameters.
replaced my secondary vacuum system. It was holding vacuum.
replaced vacuum solenoid
checked fuel pressure. The pumps were putting out on the low end. Replaced both pumps, same problem
checked TPS
checked fuel press. regulator
replaced spark plugs
drove without intake on
checked coil packs
checked plug wires
checked MAP sensor.
checked IAC
checked vacuum leaks.

At this point I had tested everything in the service manual for hesitation and surges that exhibit the problem with the power key on.

I then borrowed a diacom and hooked up a laptop. Well, the results finally showed me something I could use. I found that the exhaust on the left and right sides were going lean during the moment of the hesitation. Normal O2 sensors do cycle back and forth between 300-800 or so mv at idle. But during acceleration, you should see somewhat of a symmetric exhaust O2 profile. Mine did not show that. Here is a screenshot of the Diacom output. http://vettefinders.com/zr1/diacom2.jpg Notice where the vertical line is. At that moment I had the hesitation. The corresponding values are on the left side. Throttle position was 82% and accelerating. The O2 sensor was getting richer, then dropped to 82 mv during the hesitation. Very lean.

Now I suspected that something was causing the cylinders (both sides) to get a burst of air at about the time the secondary system was activating. I thought it had to be either the butterflies opening or something in the throttle body.

I removed the plenum (for about the 10th time) and took a closer look at the actuator operation. If I hooked up a vacuum pump to the actuators, they appear to operate very smoothly. I put my finger on them to see if I could feel any indication of binding while they were opening the butterflies. I could not feel anything. Next I pushed on the actuator arm and on both of them, I felt them bind while they were opening. I would think that applying vacuum to the actuators and NOT pushing them with my finger (not applying vacuum) would be perfectly representative of their actual operation. I flipped the actuators again and swapped them out with new ones. The same thing occurs on all four. I then decided to put the pin from the butterfly arm into the hole of the actuator arm closest to the body of the actuator. This does two things. It makes the normal deactivated (power key off) position of the butterflies open about 15 degrees and also reduces the distance the arm has to travel. In this position, the actuator arms operated smoothly when vacuum was applied as well as when pushing the arm with my finger. The amount of vacuum required to open the secondaries fully before and after I made this change was 7-8 in. Hg.

I reassembled and went for a test drive. What do you know, no stumble or hesitation! All I feel is a little acceleration when the secondaries kick in now. So, I am left with drawing the conclusion that either the actuators were sticking (which it did not appear to be the case under vacuum operation) or that when the butterflies opened they were popping open and causing the lean condition.

I took a look at the diacom results after my change and I do not see a lean condition (as I expected from drivability improvement). My next step is to get a new chip calibration. The computer appears to be able to handle the calibration for leaving the butterflies in this position, according to the diacom results (02 sensor and block learn) .

bhamvett

Chris,
I think you might have solved my problem.Although I don't have O2
sensors,when the car hesitates at idle(which it does not do often),I
do get a real harsh smell from the exhaust system.It smells much
stronger than the normal exhaust smell.And also when it does hesitate,
if you put your foot into the throttle it goes away,which would support
your finding a actuator problem with your car.Glad you found the problem.
I know firsthand how annoying this can be!
Thank's again,
Steve

DDSLT5

Steve - you HAVE O2 sensors. If you don't, then you have the prettiest paper weight in the history of the world. Even though the stock exhaust manifolds are gone, the O2 sensors still have a home in the headers.

:seeya

Chris@VetteFinders

Agreed, you have to have the sensors on your engine.

This link has some pictures for you
http://corvetteactioncenter.com/foru...threadid=14272

on this image #4 is an actuator




[Modified by Chris@VetteFinders, 9:21 AM 7/17/2003]

bhamvett

Got ya.
Thank's
Steve