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.

[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

[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]

Originally Posted by 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.

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]

Originally Posted by secondchance

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....