All going well, then "boom"

[JSad]

I have a 91 ZR-1 with 53k miles on it that I bought a couple years ago. It was not well loved in the past. I have slowly been fixing things as needed. Mechanically so far I have repaired all the oil leaks, replaced the oil pressure switch, had the transmission rebuilt (bad syncros) including light weight flywheel and short shifter, added Heibeck chip, deleted the resonator, added performance mufflers, changed all fluids, fixed some electrical issues, have done a little body work and general detailing. Suspension was next project in line.

So, now the issue. the car has been running great. I parked it 3 weeks ago while I was refurbishing the top and doing some weather stripping. Today is a beautiful sunny Oklahoma day so I was going to drive it to work. When I started it, it "backfired", the noise coming from the engine bay, not out the exhaust it seemed. Then it died immediately. It would start but ran very rough and would not idle. Didn't see any smoke or obvious issues. I had to get to work so I didn't spend much time on it.

The simple solution is to send it to Heibeck and have a 510 package done but right now I need a slightly more affordable option, any suggestions on where I start looking for the problem?

[carter200]

Pull the plenum, attach the hose that blew off and start it up to see if ok now. Don?t fill with water till ok if you are still running the TB wet.

[TX '90 ZR1]

I agree with Carter that it is a hose blown loose from the backfire. A fairly common occurrence if you let off of the key too soon during start up.
Before you pull the plenum, check the hose to the fuel pressure regulator. It is located at the rear of plenum and can be accessed without removing anything.
:cheers:

[Ccmano]

The vacuum hose that usually blows is the one from the back of the plenum to the MAP sensor at the back of the plenum. No need to pull the plenum, just reach under the MAP sensor (its tricky) and plug it back in again. You may have to undo the MAP sensor mounting bracket bolts to get at it. Been there done that. Next time you start your car keep your foot off the gas pedal. It contributes to back firing.
H
:cheers:

[secondchance]

Agree with Ccmano.

[JSad]

Thank you all for the input. I will check the accessible hoses and let you know how it goes. If I end up pulling the plenum guess I can do some detail clean up and maintenance at that time.

[wfot]

I agree with CCMano too, very common and very easy to resolve with no tools just find the map sensor and make sure the small hose is attached at both ends.

the fueling is dependent on map sensor vacuum readings, if the sensor has no vacuum, the fueling goes to hell fast.

[JSad]

You all nailed it. The hose at the map sensor came loose. I reconnected it and it is running fine. Thank you for sharing your knowledge of the beast. Gotta love this ZR-1 group.

[secondchance]

You all nailed it. The hose at the map sensor came loose. I reconnected it and it is running fine. Thank you for sharing your knowledge of the beast. Gotta love this ZR-1 group.

And, restrain from zip-tieing to avoid happening again. If you do, you run a risk of blowing up stream where it?s more difficult to get to. Unless, you enjoy removing and installing the plenum.

[JSad]

And, restrain from zip-tieing to avoid happening again. If you do, you run a risk of blowing up stream where it?s more difficult to get to. Unless, you enjoy removing and installing the plenum.

Ahhh, wise words Sensei. That crossed my mind....

[Matt B]

Great to hear your Z is back on the road.

And it's an awesome thread with a long term soothing effect - whenever my Z will have some issues that look damn serious like this one, I'll FIRST post it here and THEN panic. Not the other way around as I'd normally do, hahahaha.
Great community, so glad having the honour to become part of it!

Sent from my J9110 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[JSad]

Thanks Matt, this is a great place to go before the panic sets in.

[PhillipsLT5]

Try to hold the key to on position a little longer on start up, don't let it go early or may blow it off again

[JSad]

I drove the car to work today and the idle is running 1500 to 2000 rpm. Guess there may be a vacuum leak? I will check and make sure I got the MAP hose on when I get home this evening.

[Matt B]

Try to hold the key to on position a little longer on start up, don't let it go early or may blow it off againWhere's the technical benefit of this action that leads to the improvement?

Sent from my J9110 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[DRM500RUBYZR-1]

Where's the technical benefit of this action that leads to the improvement?

Sent from my J9110 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

The technical benefit simply is years of experience with LT-5's.

Having blown the same hose off on my first ZR-1 back in 93 or so, then again, once the following year, is when someone first mentioned to me the procedure of longer cranking episodes, especially after long periods of sitting.
Since 95 that has never happened to me again.

Wish I could lay claim to being the genius who figured it out, but I am happy just being the follower as I have never had to fiddle with it again.

However, if no one claims ownership to this idea, I likely will simply decree that the "Marty ZR-1 Starting Theorem" was discovered in the early 90's and that someone should nominate me for the Nobel prize or build a statue or something.
Maybe just award me $10,000,000.00 instead.

By the way.
It works.
:cheers:
Marty

[Ccmano]

I drove the car to work today and the idle is running 1500 to 2000 rpm. Guess there may be a vacuum leak? I will check and make sure I got the MAP hose on when I get home this evening.

Yup, you have a vacuum leak somewhere else, likely another hose.
We're here to help... we were all newbies at some point.
H
:cheers:

[PhillipsLT5]

The technical benefit simply is years of experience with LT-5's.

Having blown the same hose off on my first ZR-1 back in 93 or so, then again, once the following year, is when someone first mentioned to me the procedure of longer cranking episodes, especially after long periods of sitting.
Since 95 that has never happened to me again.

Wish I could lay claim to being the genius who figured it out, but I am happy just being the follower as I have never had to fiddle with it again.

However, if no one claims ownership to this idea, I likely will simply decree that the "Marty ZR-1 Starting Theorem" was discovered in the early 90's and that someone should nominate me for the Nobel prize or build a statue or something.
Maybe just award me $10,000,000.00 instead.

By the way.
It works.
:cheers:
Marty
Thanks Marty:thumbsup:

[Matt B]

.

By the way.
It works.
:cheers:
Marty

Well, that's all we have to know in the end :). I was just wondering what difference a longer cranking process has to understand the cause/effect here.
But maybe the ECM applies a different spark timing or air/fuel mixture as long as the key is turned. Who knows...

Anyway, I'll consider the Marty Code from now on :)

Sent from my J9110 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[tf95ZR1]

Try to hold the key to on position a little longer on start up, don't let it go early or may blow it off again

I have owned my Z for over 20 years. I also subscribe to the "keep your foot off the accelerator" and "hold it a little longer" (Marty's :)) Theory. This is just insurance that the engine has indeed started and will stay running. Especially if you are in a hurry, how many times have you let off too soon just to hear the engine die out? In the LT5 this could lead to a Ka-Boom!

And what's the big deal: can't hold it a little longer? :) JK

PS: Typing this I didn't want to look TOO STUPID by interchanging engine and motor. So....

"engine = a device that uses combustion or heat to produce motion
motor = a device that converts electric (or hydraulic) energy into motion"

https://jakubmarian.com/difference-between-engine-and-motor/

Now you are educated!

[A26B]

I have owned my Z for over 20 years. I also subscribe to the "keep your foot off the accelerator" and "hold it a little longer" (Marty's :)) Theory. ..............

PS: Typing this I didn't want to look TOO STUPID by interchanging engine and motor. So....

"engine = a device that uses combustion or heat to produce motion
motor = a device that converts electric (or hydraulic) energy into motion"

https://jakubmarian.com/difference-between-engine-and-motor/

Now you are educated!

I also subscribe to "both" starting requirements, AND Engine vs Motor definition!

Great post Ted!

[WARP TEN]

The technical benefit simply is years of experience with LT-5's.

Having blown the same hose off on my first ZR-1 back in 93 or so, then again, once the following year, is when someone first mentioned to me the procedure of longer cranking episodes, especially after long periods of sitting.
Since 95 that has never happened to me again.

Wish I could lay claim to being the genius who figured it out, but I am happy just being the follower as I have never had to fiddle with it again.

However, if no one claims ownership to this idea, I likely will simply decree that the "Marty ZR-1 Starting Theorem" was discovered in the early 90's and that someone should nominate me for the Nobel prize or build a statue or something.
Maybe just award me $10,000,000.00 instead.

By the way.
It works.
:cheers:
Marty

The check is in the mail, Marty. Honest. --Bob

[JSad]

Yup, you have a vacuum leak somewhere else, likely another hose.
We're here to help... we were all newbies at some point.
H
:cheers:

Thanks, I downloaded Marc's "Finding and Fixing Vacuum Leaks" and will begin going through the systems this weekend to see what is going on.

[We Gone]

Order a new map hose from Jerry's every ZR-1 I have owned the hose gets oil saturated over time and does not hold as well.

[JSad]

I looked at his website today. I am less than an hour away so may just take a nice ride down Route 66 and pick it up in person.