Notices
C4 ZR-1 Discussion General ZR-1 Corvette Discussion, LT5 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track

90 zr1 falls on its face need help

 
Old 07-02-2019, 02:54 PM
  #1  
ZRConekiller
Junior Member
Thread Starter
 
ZRConekiller's Avatar
 
Member Since: Nov 2018
Location: Halifax Nova Scotia
Posts: 16
Received 1 Like on 1 Post
Default 90 zr1 falls on its face need help

Hey everyone so I had my 90 zr1 at a weekend long autocross event this weekend and charging out of the gate when relatively cold the car pulled strong all the way to 7200. Now after a few runs the car would come up to about 4000 rpm and it would fall on its face lack of power short shift the car and same thing. The weird part is that after I made the sweeping right hander the power was back and the car felt great for the rest of the run. Coolant temp was 98 degrees c so 208ish f. Anyone have any ideas? Yes all 16 injectors are original but we don't have any of the ethanol in or fuel you guys have in the states. I have another event coming up this weekend so any help would be greatly appreciated thanks.
ZRConekiller is online now  
Old 07-02-2019, 07:23 PM
  #2  
ccmano
CF Senior Member
 
ccmano's Avatar
 
Member Since: Aug 2005
Location: Sparks NV
Posts: 1,457
Received 52 Likes on 50 Posts
Default

This must be going around.... it’s not injectors if it idles well, sounds like a clogged fuel filter or bad secondary fuel pump.
Check fuel pressure should be ~48-55 psi without vacuum to the regulator and ~38-45 with vacuum. I just did one with the same issue. Turned out to be the filter.

With the car cold, hook up a pressure gauge then simply turn on the ignition, don’t start the car. You should see 48-55 psi that way too. Another good way to test is to check the amp draw of the pumps. Good pumps draw 4-5 amps each, 8-10 amps when both pumps run. Less and your pumps are going bad. It’s nicely written up by Paul here...at post #7.

http://www.zr1.net/forum/showthread.php?p=136108
H
ccmano is offline  
The following users liked this post:
ZRConekiller (07-02-2019)
Old 07-04-2019, 01:00 AM
  #3  
jay1055
CF Senior Member
 
Member Since: Apr 2012
Posts: 415
Received 8 Likes on 8 Posts
Default

Collapsing air intake duct ?
jay1055 is offline  
Old 07-04-2019, 07:00 AM
  #4  
Rkreigh
CF Senior Member
 
Member Since: Dec 1999
Location: Alexandria, Virginia, USA VA
Posts: 7,946
Received 101 Likes on 87 Posts
Default

the older air ducts suck closed. do a samco or put a coffee can in the stocker to keep it open

make sure the fuel pumps are good. easy way is to connect a fuel pressure gauge to the fuel rail shrader valve and tape it to the windshield.

if fuel pressure drops off check pumps.

check for sticky secondaries not openings and any codes

often injectors fail when hot, ask me how I know. warn the car up and you can ohm them out through the connnector harness without pulling the plenum

see zr1 specialist for a good write up on how to do this, it will save you a plenum pull

keep us posted and good luck

FYI

the FSM is the bomb for trouble shooting, I have a few spares for the early cars if needed. selling them for
$40

Last edited by Rkreigh; 07-04-2019 at 07:05 AM.
Rkreigh is offline  
Old 07-04-2019, 11:08 AM
  #5  
Paul Workman
CF Senior Member
 
Paul Workman's Avatar
 
Member Since: Oct 2004
Location: "Below I-80" Illinois
Posts: 5,664
Received 236 Likes on 211 Posts
Default

One other thing...

When under hood temps were hot, my 1990 too would fall on it nose around 4000 rpm. Turned out to be the accordion hose between the air filter and the Throttle Body was collapsing.

I fashioned an aluminum sleeve that fits snugly inside that hose. Works like a charm! Marc Haibeck also provides some little wire hoops that fit inside of that tube that keep it from collapsing.

Either solution will prevent that hose from crushing at WOT/hot under hood conditions.
Paul Workman is offline  
Old 07-05-2019, 05:57 AM
  #6  
Rkreigh
CF Senior Member
 
Member Since: Dec 1999
Location: Alexandria, Virginia, USA VA
Posts: 7,946
Received 101 Likes on 87 Posts
Default

Originally Posted by Paul Workman View Post
One other thing...

When under hood temps were hot, my 1990 too would fall on it nose around 4000 rpm. Turned out to be the accordion hose between the air filter and the Throttle Body was collapsing.

I fashioned an aluminum sleeve that fits snugly inside that hose. Works like a charm! Marc Haibeck also provides some little wire hoops that fit inside of that tube that keep it from collapsing.

Either solution will prevent that hose from crushing at WOT/hot under hood conditions.

we saw this clearly happening when we dyno the Z
Rkreigh is offline  
Old 07-05-2019, 12:04 PM
  #7  
ccmano
CF Senior Member
 
ccmano's Avatar
 
Member Since: Aug 2005
Location: Sparks NV
Posts: 1,457
Received 52 Likes on 50 Posts
Default

Originally Posted by jay1055 View Post
Collapsing air intake duct ?
Certainly possible. I had it on mine early on. I built two hoops out of 1/8 welding rod similar to what Haibeck sells and installed them about 1/3 in from both ends. Problem solved.

http://www.zr1specialist.com/HAT%20W...ucts/hoops.htm

H
ccmano is offline  
Old 07-08-2019, 07:26 PM
  #8  
ucfchris84
Junior Member
 
Member Since: Nov 2015
Posts: 8
Received 4 Likes on 2 Posts
Default

I had a similar problem not the same.... Car would idle fine take off and anything past half throttle would fall on its face...... we swapped injectors and put some really nice all stainless injectors in and the car runs like a dream.. 90 zr1
ucfchris84 is offline  
 


Thread Tools
Search this Thread
Quick Reply: 90 zr1 falls on its face need help


Contact Us - About Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: