Post Plenum Pull Problem - ZR-1 Net Registry Forums

pantera1683 · 10-31-2010

I just finished with my plenum pull, changed alternator, wires, and coils. Now I have a misfire and backfire through the exhaust that is getting progressively better. My idle goes between 1300 and 750 and I do have a slight vacuum leak at the fuel pressure regulator that I will address this afternoon. I am just worried about damaging the car and want to make sure that the vacuum leak is my problem. Any ideas?

LGAFF · 10-31-2010

Pulling any codes.....misfire could be vac leak or ign wire crossed, I would not drive it with the misfire....

pantera1683 · 10-31-2010

I think the vacuum leak is worse than I thought, there is a loud howling whistle coming from underneath the plenum.

bldavis11 · 10-31-2010

Double check, and then tripple check, the MAP sensor hose at the very rear of the plenum. Another vac leak source (that you swear is under the plenum and actually isn't) to check is the PCV valve hose on the driver's side towards the rear of the plenum. You might actually have to pull that hose to investigate for a crack/split in the rubber... very, very common.

Let us know.

pantera1683 · 10-31-2010

Map, PCV, and all external hoses look good

tomtom72 · 10-31-2010

I know there is one vac hose at the right side of the T/Body....it's off all by it's lonesome at the right side lower rear of the T/Body... a nipple that faces backwards on a 90 anyway(?). That one is easy to have come undone while you are reconnecting the DIS stuff.

Tom

pantera1683 · 10-31-2010

Turns out I crossed #6 and #8 plug wires. It runs really well now. As for the loud hissing sound, turns out it's the LT1 alternator touching the plenum and causing a vibration. I will have to lift the plenum and clearance the alternator a bit with the grinder. As soon as I get my stock alternator rebuilt it goes back in.

Thanks to everyone for the help.

tomtom72 · 11-01-2010

Good deal. I love repairs that don't cost anything.

bldavis11 · 11-02-2010

Glad it worked out with an easy fix.

10-31-2010	#1
pantera1683 Join Date: Mar 2010 Location: Fort Worth, TX Posts: 396	Post Plenum Pull Problem I just finished with my plenum pull, changed alternator, wires, and coils. Now I have a misfire and backfire through the exhaust that is getting progressively better. My idle goes between 1300 and 750 and I do have a slight vacuum leak at the fuel pressure regulator that I will address this afternoon. I am just worried about damaging the car and want to make sure that the vacuum leak is my problem. Any ideas?

10-31-2010	#2
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,193	Re: Post Plenum Pull Problem Pulling any codes.....misfire could be vac leak or ign wire crossed, I would not drive it with the misfire.... __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

10-31-2010	#3
pantera1683 Join Date: Mar 2010 Location: Fort Worth, TX Posts: 396	Re: Post Plenum Pull Problem I think the vacuum leak is worse than I thought, there is a loud howling whistle coming from underneath the plenum.

10-31-2010	#4
bldavis11 Join Date: Mar 2006 Location: Portsmouth, VA Posts: 245	Re: Post Plenum Pull Problem Double check, and then tripple check, the MAP sensor hose at the very rear of the plenum. Another vac leak source (that you swear is under the plenum and actually isn't) to check is the PCV valve hose on the driver's side towards the rear of the plenum. You might actually have to pull that hose to investigate for a crack/split in the rubber... very, very common. Let us know.

10-31-2010	#5
pantera1683 Join Date: Mar 2010 Location: Fort Worth, TX Posts: 396	Re: Post Plenum Pull Problem Map, PCV, and all external hoses look good

10-31-2010	#6
tomtom72 Join Date: Dec 2004 Location: Jacksonville, FL USA Posts: 4,645	Re: Post Plenum Pull Problem I know there is one vac hose at the right side of the T/Body....it's off all by it's lonesome at the right side lower rear of the T/Body... a nipple that faces backwards on a 90 anyway(?). That one is easy to have come undone while you are reconnecting the DIS stuff. Tom __________________ 1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member

10-31-2010	#7
pantera1683 Join Date: Mar 2010 Location: Fort Worth, TX Posts: 396	Re: Post Plenum Pull Problem Turns out I crossed #6 and #8 plug wires. It runs really well now. As for the loud hissing sound, turns out it's the LT1 alternator touching the plenum and causing a vibration. I will have to lift the plenum and clearance the alternator a bit with the grinder. As soon as I get my stock alternator rebuilt it goes back in. Thanks to everyone for the help.

11-01-2010	#8
tomtom72 Join Date: Dec 2004 Location: Jacksonville, FL USA Posts: 4,645	Re: Post Plenum Pull Problem Good deal. I love repairs that don't cost anything. __________________ 1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member

11-02-2010	#9
bldavis11 Join Date: Mar 2006 Location: Portsmouth, VA Posts: 245	Re: Post Plenum Pull Problem Glad it worked out with an easy fix.