Basic Diagnostics YOU CAN DO IT! - ZR-1 Net Registry Forums

Ccmano · 02-03-2020

Anyone who has been around our ZR-1’s long enough understands that on these ~30 year old cars if something hasn’t already gone wrong, something will eventually. When that day comes we have two options. 1 try and fix it yourself. 2 Pay someone else to fix it. Given the lack of competent LT5 specific repairs shops around the country, the likelihood is that many will try to fix it themselves.

The first temptation is to go to places on the internet like this forum or possibly a Facebook group and look for answers. Very often this works well. Many issues are commonly known and their resolution is as well. That’s what makes these groups so good. Dynomites “Solutions” thread is a wonderful example.

However, as many know, there can be multiple issues that can present as a single problem or multiple problems that have a single solution. Human nature being what it is we all look for the quick fix. I’ve been guilty of it myself. Sometimes you get lucky. A certain part is suggested as a fix by several people. You replace it and the issue is resolved. But, sometimes and probably more often, you can throw multiple parts at an issue and still have the problem. All this results in wasted time and money, not to mention frustration, in trying to solve an issue. I’ve seen people sell cars because of this, when it could all have been prevented.

I’ve worked on cars for over 40 years and have been a certified MB tech. I have supervised technicians and worked corporately for 3 manufacturers. If I have learned anything, often by my own errors, it's that time spent doing proper diagnosis saves countless hours, dollars and frustration.

In our case, GM supplied its technicians and subsequently us with a fantastic diagnostic resource in the Factory Service Manuals it published for each model year. In particular for those vehicle systems governed by those early computer systems in the ECM, CCM, BCM and DIS. A high percentage of the issues encountered with our cars can be traced to these aging systems. Luckily for us GM has provided detailed diagnostic trees for most drivability issues and for any of the multitude of codes that these systems can show. While not necessarily pinpointing the problem, these Codes and diagnostic trees can walk you straight to the issue without needless expense in time or money. The caveat is that a certain degree of technical ability is required to follow these trees and reach the correct conclusion.

The purpose of my post here is to urge ZR-1 owners to first buy a copy of the FSM, the LT5 Manual and the Electrical Manual for their year car. Then secondly, if you do have an issue, check the systems for codes and use the diagnostic trees in the manual, along with input from knowledgeable members, to properly diagnose your problem. Don’t get caught in the expensive and frustrating habit of throwing parts at a problem only to find wiring issue. Or, post about a problem, here or elsewhere, and get a dozen different potential solutions from people who “think” they had that issue and such and such fixed it.

We are all here to help make ZR-1 ownership a positive and rewarding experience. But you do need to help yourself so some degree. Get at least some of the tools to do that. The Manuals noted above and a good code reader, preferably a Tech1, the factory diagnostic tool. They are regularly available on eBay for $250 - $500. You likely paid tens of thousands of your Z. Don’t skimp on the basic tools.

Hoping your Z ownership experience is a positive one.
H

TX '90 ZR1 · 02-04-2020

THANKS for posting this!!
Very sage advice!!

32valvZ · 02-04-2020

Luckily I havent had a code issue up to now. I have an MT2500 Snap On scanner. Would I be better off selling it and buying a Tech 1?

We Gone · 02-04-2020

Great post I also have a very nice scanner Genisys EVO 5.0 that I can use on many cars from OBDI up to 2011 of different makes and models. for some diagnostics on our cars can only be done with a tech 1.

Ccmano · 02-04-2020

Quote:

Originally Posted by 32valvZ

Luckily I havent had a code issue up to now. I have an MT2500 Snap On scanner. Would I be better off selling it and buying a Tech 1?

As you can see other OBD1 scanners work to a large degree. I like the ability to know that what is being described in the manual is exactly what is see on my Tech1 and as noted some things can only be done on a Tech1, 1a or Tech2.
H

Ccmano · 02-04-2020

I don’t want to give the wrong impression here. With some of these diagnostics it’s not just a simple matter of plugging in the scanner and “bang” there’s the answer. In addition to scanner readings many of these diagnostics require voltage, ohm and continuity testing of the wiring harness, modules, relays and switches. That takes a good automotive volt/ohm meter, some know how and practice. This is where help from fellow members come in. To some this will be daunting. You’ll know pretty quickly if your cut out for this or if it’s time to hand it off to a professional. The point being your not wasting time and money throwing parts at it and going further down the road to frustration.
H

rush91 · 02-04-2020

When I bought my Z, thankfully all manuals were included. They have saved me countless $ by reading and following the step by step instructions GM layed out 30 years ago. A MUST for all LT5 owners.....

ZWILD1 · 02-05-2020

Your car may not show any codes either. Know your car and how it feels and sounds. I could tell that my first ZR1 just didn't have the same feeling of power. What you said about we often look for the quick fix or just how we look at things can affect our choices. My case of the car running not as good as before holds true. It all started right after I filled up at the service station. So in thinking it must have been related I installed a new fuel filter and then when that didn't resolve the problem I drained the tank and refilled it.

No codes were ever present. The car just was down on power a bit. I then looked at the plugs, wires and coils which all tested ok. I have had a coil go bad and it didn't feel like that. Coil was easy to figure out by looking at the plugs. Then when found a plug that was wet with fuel looked at the other plug that shared the same coil and there it was. So I looked at the injectors next. Being a 91 with almost 90K miles by this time some were marginal while others were in need of replacing. I bought 16 new injectors and installed them.

Car ran better but still the power was off. After talking to my friend who sold me the car and retracing what I had done he said well maybe one or both of the fuel pumps were not up to snuff. I should have tested them but just went ahead and replaced them both buying new ones from Chevrolet. Still it wasn't right. This time I called Marc Haibeck and after discussing with him he pointed out the obvious. I had replaced everything but the regulator. It wasn't leaking fuel and when you pulled the vacuum line there was no signs of fuel either. I ordered one from Chevrolet and pulled the plenum once more to install. She was running like never before.

It ran better than it had. So in the end it was the fuel pressure regulator. It did need the injectors. Pumps not so. It was a fuel problem after all. It had proper pressure at an idle. I just didn't have a line long enough to tape the gauge to the windshield and observe while driving at speed. Had I done that it would have shown the issue. The fact it started when I filled up at the service station was just a coincidence. I also worked as a mechanic doing front ends, alignments, brakes, anything suspension. I had built engines and installed them in my own vehicles.

Paul Workman · 02-06-2020

Dittos to ccmano (Hans) on the FSM. I can say that when I got mine, I immediately sat down and read through them, cover to cover which provided me with a very good overall knowledge of the ZR-1 systems - fofilling the first rule of effective troubleshooting: KNOW HOW THE SYSTEM WORKS!

Combined with an OBD-I scanner and I was well on my way to fixing or at least identifying any issues I've encountered with the Zs in our garage.

FSM + OBD-1 scanner (with the ability to capture an event) will go a long way to being way ahead of probably 99% of the dealers you might otherwise be relegated to for help.

daviddu79 · 02-09-2020

My ZR-1 is broken, I changed the spark plugs, ignition coils, spark plugs. Now I think of the injectors. When I have new candles, it works well and the next day it doesn't turn round and I have a cylinder that smells of petrol.

02-03-2020	#1
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Basic Diagnostics YOU CAN DO IT! Anyone who has been around our ZR-1’s long enough understands that on these ~30 year old cars if something hasn’t already gone wrong, something will eventually. When that day comes we have two options. 1 try and fix it yourself. 2 Pay someone else to fix it. Given the lack of competent LT5 specific repairs shops around the country, the likelihood is that many will try to fix it themselves. The first temptation is to go to places on the internet like this forum or possibly a Facebook group and look for answers. Very often this works well. Many issues are commonly known and their resolution is as well. That’s what makes these groups so good. Dynomites “Solutions” thread is a wonderful example. However, as many know, there can be multiple issues that can present as a single problem or multiple problems that have a single solution. Human nature being what it is we all look for the quick fix. I’ve been guilty of it myself. Sometimes you get lucky. A certain part is suggested as a fix by several people. You replace it and the issue is resolved. But, sometimes and probably more often, you can throw multiple parts at an issue and still have the problem. All this results in wasted time and money, not to mention frustration, in trying to solve an issue. I’ve seen people sell cars because of this, when it could all have been prevented. I’ve worked on cars for over 40 years and have been a certified MB tech. I have supervised technicians and worked corporately for 3 manufacturers. If I have learned anything, often by my own errors, it's that time spent doing proper diagnosis saves countless hours, dollars and frustration. In our case, GM supplied its technicians and subsequently us with a fantastic diagnostic resource in the Factory Service Manuals it published for each model year. In particular for those vehicle systems governed by those early computer systems in the ECM, CCM, BCM and DIS. A high percentage of the issues encountered with our cars can be traced to these aging systems. Luckily for us GM has provided detailed diagnostic trees for most drivability issues and for any of the multitude of codes that these systems can show. While not necessarily pinpointing the problem, these Codes and diagnostic trees can walk you straight to the issue without needless expense in time or money. The caveat is that a certain degree of technical ability is required to follow these trees and reach the correct conclusion. The purpose of my post here is to urge ZR-1 owners to first buy a copy of the FSM, the LT5 Manual and the Electrical Manual for their year car. Then secondly, if you do have an issue, check the systems for codes and use the diagnostic trees in the manual, along with input from knowledgeable members, to properly diagnose your problem. Don’t get caught in the expensive and frustrating habit of throwing parts at a problem only to find wiring issue. Or, post about a problem, here or elsewhere, and get a dozen different potential solutions from people who “think” they had that issue and such and such fixed it. We are all here to help make ZR-1 ownership a positive and rewarding experience. But you do need to help yourself so some degree. Get at least some of the tools to do that. The Manuals noted above and a good code reader, preferably a Tech1, the factory diagnostic tool. They are regularly available on eBay for $250 - $500. You likely paid tens of thousands of your Z. Don’t skimp on the basic tools. Hoping your Z ownership experience is a positive one. 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. Last edited by Ccmano; 02-03-2020 at 08:56 PM.

02-04-2020	#2
TX '90 ZR1 Join Date: Oct 2017 Location: TX Posts: 2,035	Re: Basic Diagnostics YOU CAN DO IT! THANKS for posting this!! Very sage advice!! __________________ Kenny 1990 #442

02-04-2020	#3
32valvZ Join Date: Nov 2007 Location: Sunshine State Posts: 1,071	Re: Basic Diagnostics YOU CAN DO IT! Luckily I havent had a code issue up to now. I have an MT2500 Snap On scanner. Would I be better off selling it and buying a Tech 1? __________________ [B]1990 #2815[/B] [COLOR="Red"][B]Red/Red[/B][/COLOR] Ported Plenum & IH (by Pete) Haibeck Chip Rebuilt FPR (by Phil) FIC Injectors Watson LT Headers 3" Stainless Works exhaust Lingenfelter Open Air Lid Bill B Built Transmission Shifter & C Beam Plates [FONT=Impact][COLOR=red]1992 [COLOR=black]#[/COLOR] 091[/COLOR][/FONT] [FONT=Impact][COLOR=#ff0000]Red/[COLOR=silver]Gray[/COLOR][/COLOR][/FONT] [B]SOLD[/B]

02-04-2020	#4
We Gone Join Date: Apr 2004 Location: ATL. GA. Posts: 2,170	Re: Basic Diagnostics YOU CAN DO IT! Great post I also have a very nice scanner Genisys EVO 5.0 that I can use on many cars from OBDI up to 2011 of different makes and models. for some diagnostics on our cars can only be done with a tech 1. __________________ Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold

02-04-2020	#6
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: Basic Diagnostics YOU CAN DO IT! I don’t want to give the wrong impression here. With some of these diagnostics it’s not just a simple matter of plugging in the scanner and “bang” there’s the answer. In addition to scanner readings many of these diagnostics require voltage, ohm and continuity testing of the wiring harness, modules, relays and switches. That takes a good automotive volt/ohm meter, some know how and practice. This is where help from fellow members come in. To some this will be daunting. You’ll know pretty quickly if your cut out for this or if it’s time to hand it off to a professional. The point being your not wasting time and money throwing parts at it and going further down the road to frustration. 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. Last edited by Ccmano; 02-04-2020 at 05:59 PM.

02-04-2020	#7
rush91 Join Date: Feb 2016 Location: Carterville Illinois Posts: 850	Re: Basic Diagnostics YOU CAN DO IT! When I bought my Z, thankfully all manuals were included. They have saved me countless $ by reading and following the step by step instructions GM layed out 30 years ago. A MUST for all LT5 owners.....

02-05-2020	#8
ZWILD1 Join Date: Aug 2004 Location: Spring Grove ,Pa. Posts: 257	Re: Basic Diagnostics YOU CAN DO IT! Your car may not show any codes either. Know your car and how it feels and sounds. I could tell that my first ZR1 just didn't have the same feeling of power. What you said about we often look for the quick fix or just how we look at things can affect our choices. My case of the car running not as good as before holds true. It all started right after I filled up at the service station. So in thinking it must have been related I installed a new fuel filter and then when that didn't resolve the problem I drained the tank and refilled it. No codes were ever present. The car just was down on power a bit. I then looked at the plugs, wires and coils which all tested ok. I have had a coil go bad and it didn't feel like that. Coil was easy to figure out by looking at the plugs. Then when found a plug that was wet with fuel looked at the other plug that shared the same coil and there it was. So I looked at the injectors next. Being a 91 with almost 90K miles by this time some were marginal while others were in need of replacing. I bought 16 new injectors and installed them. Car ran better but still the power was off. After talking to my friend who sold me the car and retracing what I had done he said well maybe one or both of the fuel pumps were not up to snuff. I should have tested them but just went ahead and replaced them both buying new ones from Chevrolet. Still it wasn't right. This time I called Marc Haibeck and after discussing with him he pointed out the obvious. I had replaced everything but the regulator. It wasn't leaking fuel and when you pulled the vacuum line there was no signs of fuel either. I ordered one from Chevrolet and pulled the plenum once more to install. She was running like never before. It ran better than it had. So in the end it was the fuel pressure regulator. It did need the injectors. Pumps not so. It was a fuel problem after all. It had proper pressure at an idle. I just didn't have a line long enough to tape the gauge to the windshield and observe while driving at speed. Had I done that it would have shown the issue. The fact it started when I filled up at the service station was just a coincidence. I also worked as a mechanic doing front ends, alignments, brakes, anything suspension. I had built engines and installed them in my own vehicles. __________________ 91 Turquoise Metallic Haibeck 525 #0134

02-06-2020	#9
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: Basic Diagnostics YOU CAN DO IT! *Dittos to ccmano (Hans) on the FSM.* I can say that when I got mine, I immediately sat down and read through them, cover to cover which provided me with a very good overall knowledge of the ZR-1 systems - fofilling the first rule of effective troubleshooting: KNOW HOW THE SYSTEM WORKS! *Combined with an OBD-I scanner* and I was well on my way to fixing or at least identifying any issues I've encountered with the Zs in our garage. FSM + OBD-1 scanner (with the ability to capture an event) will go a long way to being way ahead of probably 99% of the dealers you might otherwise be relegated to for help. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

02-09-2020	#10
daviddu79 Join Date: May 2011 Location: france Posts: 53	Re: Basic Diagnostics YOU CAN DO IT! My ZR-1 is broken, I changed the spark plugs, ignition coils, spark plugs. Now I think of the injectors. When I have new candles, it works well and the next day it doesn't turn round and I have a cylinder that smells of petrol. __________________ ZR-1 Red and Black vin 1554 Last edited by daviddu79; 02-09-2020 at 05:09 PM.