ZR-1 Net Registry Forums  

Go Back   ZR-1 Net Registry Forums > C4 ZR-1 > C4 ZR-1 Technical Postings

Reply
 
Thread Tools Display Modes
Old 05-16-2021   #1
jrd1990zr1
 
jrd1990zr1's Avatar
 
Join Date: Dec 2005
Location: Delanson, NY
Posts: 914
Default 1990 MY Hesitation/ stumble of engine

Was having this problem late last year, When at idle cold there seems to be a miss, like a bad wire. When the engine warms up the situation is not quite as bad but if you step on it the engine hesitates then seems to catch.

Over the winter I pulled the plenum, new set of GM wires, checked the coils. This Spring, same problem. Changed the injectors (FIC) about 9 years ago so they were supposed to be ethanol compliant and at the same time changed the plugs. This was about 30,000 miles ago. Car has 62,000 on it I don't drive it a lot each year.

I am at a loss, seems like next step is another set of plugs?

Can a set of FIC injectors go bad at about 30,000 miles?

Any suggestions on how to diagnose this issue? Is there a simple procedure to check the injectors without pulling the plenum?

Any suggestions would be appreciated. Thanks.
__________________

1968 convertible Lemans Blue,
1986 coupe Medium Blue NCRS Top Flight (sold),
1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold),
1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018,
2003 Anniversary Red Convertible (sold)
jrd1990zr1 is offline   Reply With Quote
Old 05-18-2021   #2
wfot
 
wfot's Avatar
 
Join Date: Jan 2009
Location: New jersey
Posts: 156
Default Re: 1990 MY Hesitation/ stumble of engine

I would check over some simple stuff. check/test the TPS, it might be worn out or in need of adjustment...

Are the plug wires fully seated on each plug?

Are the wires routed exactly like the factory manual Shows?

ZR1 specialist has a detailed way it resistance test the injectors in the car - but the problem is gets worse when the engine is hot.
wfot is offline   Reply With Quote
Old 05-18-2021   #3
jrd1990zr1
 
jrd1990zr1's Avatar
 
Join Date: Dec 2005
Location: Delanson, NY
Posts: 914
Default Re: 1990 MY Hesitation/ stumble of engine

Quote:
Originally Posted by wfot View Post
I would check over some simple stuff. check/test the TPS, it might be worn out or in need of adjustment...

Are the plug wires fully seated on each plug?

Are the wires routed exactly like the factory manual Shows?

ZR1 specialist has a detailed way it resistance test the injectors in the car - but the problem is gets worse when the engine is hot.
Thanks for the advice. Wires are properly seated and routed, I have already checked that.

Are you aware of a way to check the TPS or adjust it? I had not thought of that.
__________________

1968 convertible Lemans Blue,
1986 coupe Medium Blue NCRS Top Flight (sold),
1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold),
1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018,
2003 Anniversary Red Convertible (sold)
jrd1990zr1 is offline   Reply With Quote
Old 05-18-2021   #4
wfot
 
wfot's Avatar
 
Join Date: Jan 2009
Location: New jersey
Posts: 156
Default Re: 1990 MY Hesitation/ stumble of engine

I don't have the exact sequence at my fingertips right now, but there are 2 ways
1) back probe the middle? and black wire? and read the voltage. it should be at near .54, I think .54 is the optimal. I have used paperclips to not puncture the wire casings

2) hook up ECM reader and just read the voltage

either way the at rest voltage should be the .54 and the open fully should be around 4.7 to 5.0. the upper number is a little less important. the rest number is where you make adjustments. there are 2 torx screws, loosen and twist until you get the .54v.

also, look at the meter as you rotate the throttle open/closed several times. the numbers should be smooth and linear, if there are spots where the numbers stick or jump, the sensor is worn out. I have found GM parts work best as the fueling is designed around TPS reading and MAP readings...

I will look for the exact back probe wire combo if someone else does not jump in with it sooner

John
wfot is offline   Reply With Quote
Old 05-18-2021   #5
Ccmano
 
Ccmano's Avatar
 
Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,852
Default Re: 1990 MY Hesitation/ stumble of engine

Do you have a 1990 Factory Service Manual and a Tech1 (or similar) scanner?
H
__________________
90'ZR-1 #1461 Red/Black
Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold
08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold
05 C6 Z51 Red/Black Sold
90'ZR-1 #1723 Black/Gray Sold but not forgotten
91' Z51 L98 White Vert. My First, you always remember your first. Sold.
Ccmano is offline   Reply With Quote
Old 05-18-2021   #6
jrd1990zr1
 
jrd1990zr1's Avatar
 
Join Date: Dec 2005
Location: Delanson, NY
Posts: 914
Default Re: 1990 MY Hesitation/ stumble of engine

Quote:
Originally Posted by Ccmano View Post
Do you have a 1990 Factory Service Manual and a Tech1 (or similar) scanner?
H
I have the service manual and a set of Gordons ALDL plugs Is there a way to use the plugs to diagnose the this?
__________________

1968 convertible Lemans Blue,
1986 coupe Medium Blue NCRS Top Flight (sold),
1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold),
1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018,
2003 Anniversary Red Convertible (sold)
jrd1990zr1 is offline   Reply With Quote
Old 05-18-2021   #7
jss06c6
 
Join Date: Aug 2015
Location: Magnolia, Texas
Posts: 884
Default Re: 1990 MY Hesitation/ stumble of engine

What type of plugs are you running? I'd pull them and check gap and condition. Iridium plugs are particularly susceptible to tip erosion in a wasted spark system like the LT-5... I went through a set of NGK 7iX in 4,000 miles! Gap went from .050 to almost .070 on three of the plugs. Switched back to NGK 4177's (TR6), reduced gap to .045".. problem gone.. (stumble off idle under moderate load).

Sent from my SM-G950U using ZR-1 Net Registry mobile app
jss06c6 is offline   Reply With Quote
Old 05-18-2021   #8
jrd1990zr1
 
jrd1990zr1's Avatar
 
Join Date: Dec 2005
Location: Delanson, NY
Posts: 914
Default Re: 1990 MY Hesitation/ stumble of engine

Quote:
Originally Posted by jss06c6 View Post
What type of plugs are you running? I'd pull them and check gap and condition. Iridium plugs are particularly susceptible to tip erosion in a wasted spark system like the LT-5... I went through a set of NGK 7iX in 4,000 miles! Gap went from .050 to almost .070 on three of the plugs. Switched back to NGK 4177's (TR6), reduced gap to .045".. problem gone.. (stumble off idle under moderate load).

Sent from my SM-G950U using ZR-1 Net Registry mobile app
Yes they are AC Delco, meassured gap of #1 plug at a little over 0.040". The NGK 4177 plug (NGK V-Power Nickel Plug Number TR6 Spark Plug) came up as not fitting the 1990 ZR1 engine at O'Reillys when I looked them up. The Advance website says I need to use a NKG 6953. Am I being told the wrong information by the Advance Auto Parts website?

I think I will change out the plugs. Which one should I go for?
__________________

1968 convertible Lemans Blue,
1986 coupe Medium Blue NCRS Top Flight (sold),
1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold),
1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018,
2003 Anniversary Red Convertible (sold)

Last edited by jrd1990zr1; 05-18-2021 at 01:37 PM.
jrd1990zr1 is offline   Reply With Quote
Old 05-19-2021   #9
jrd1990zr1
 
jrd1990zr1's Avatar
 
Join Date: Dec 2005
Location: Delanson, NY
Posts: 914
Default Re: 1990 MY Hesitation/ stumble of engine

Put a new set of AC Delco in gap at 0,035" Checked MAP hoses all good. On start up it seemed smoother will take it for a ride tomorrow.

Problem solved.

My thanks to all who posted suggestions.
__________________

1968 convertible Lemans Blue,
1986 coupe Medium Blue NCRS Top Flight (sold),
1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold),
1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018,
2003 Anniversary Red Convertible (sold)

Last edited by jrd1990zr1; 05-20-2021 at 02:28 PM.
jrd1990zr1 is offline   Reply With Quote
Old 05-21-2021   #10
jss06c6
 
Join Date: Aug 2015
Location: Magnolia, Texas
Posts: 884
Default Re: 1990 MY Hesitation/ stumble of engine

Good to hear. How did your test drive go?

Sent from my SM-G950U using ZR-1 Net Registry mobile app
jss06c6 is offline   Reply With Quote
Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 10:15 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright ZR-1 Net Registry 2020