Starts and Runs Great When Cold Then.... - CamaroZ28.Com Message Board

Fuel and Ignition Fuel Pumps and Systems, Ignition and Spark Systems

Starts and Runs Great When Cold Then....

Old 03-27-2018, 11:51 AM
  #1  
Registered User
Thread Starter
 
Join Date: Aug 2000
Location: Folsom, Ca.
Posts: 108
Starts and Runs Great When Cold Then....

It runs normal on cold start - idles and accelerates smooth with no loss of power. After driving for 10 minutes it starts running rough although it still idles but has a definite loss of power as if it is missing and the timing is being retarded.

Their is no check engine light and no codes. I did find the vacuum line from the opti-spark to the intake was burned and replaced it thinking that was the problem. Then I found a ground wire from the harness near the coil was broken. Fixed that. Still running like it missing a cylinder or 2.

It is a '97 Camaro SS 6 speed car with MSD opti-spark. Any help?

Last edited by Ken Cemo; 03-27-2018 at 11:55 AM.
Ken Cemo is offline  
Old 03-27-2018, 12:12 PM
  #2  
Registered User
 
Join Date: Sep 2003
Location: Las Vegas
Posts: 1,474
Re: Starts and Runs Great When Cold Then....

You should put together a signature so we know what mods your car has.

Have you checked the plug wires? I had a plug wire that was too close to a header that caused miss fires when the car was warmed up.
DrewHMS97SS is offline  
Old 03-27-2018, 05:04 PM
  #3  
Registered User
Thread Starter
 
Join Date: Aug 2000
Location: Folsom, Ca.
Posts: 108
Re: Starts and Runs Great When Cold Then....

I did a visual on all of the plug wires. New MSD wires less than 10,000 miles ago. They look ok.
Ken Cemo is offline  
Old 03-27-2018, 05:27 PM
  #4  
Super Moderator
 
Injuneer's Avatar
 
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 66,919
Re: Starts and Runs Great When Cold Then....

Running OK cold, then deteriorating as things warm up can typically be traced to three possible causes:

1. Faulty coolant temp sensor. When the engine is cold, the PCM richens the A/F mixture, and as it warms up, starts to lean out the system. If the coolant temp is not accurate, it can stay rich too long. You would likely smell a rich exhaust if that is the case. While there are codes for the coolant temp sensor, it essentially takes total failure of the circuit to set the codes.

2. Faulty O2 sensors. The temp of the engine is one of the things that determine when the PCM runs in open loop (ignores the O2 sensor feedback), and when it switches to closed loop (adjust fueling based on O2 sensor input). But that transition usually occurs after 3 to 4 minutes. A faulty coolant temp sensor can complicate this, again delaying the transition from open loop to closed loop. If the O2 sensors are not accurate, the engine may run well in open loop, using the stored long term fuel corrections, which may be OK because the amount of correction is limited. In closed loop, the PCM uses both long term and short term fuel corrections, and a faulty O2 sensor may cause the PCM to "overcorrect".

3. Heat soak is affecting an electronic device. Most common sources of this problem are the ignition control module (ICM) and the optical cam position sensor in the Opti. These problems may or may not set codes, depending on the severity. The ICM can be tested by an auto parts store, but you have to make sure they get is good and hot while testing it. The Opti is a bit messier. The MSD Opti, depending on when it was manufactured, seems to exhibit the most problems in this respect. Even the fuel pump can heat soak and produce problems.

One of the most useful tools for trying to track down these problems is PCM data logging software. Member GaryDoug has written software for the OBD-2 cars. It is available here:

Free OBD2 scanner software - ECM/PCM - Firebird Nation

The OBD-2 version has had the least use, so we might need to get Gary over here to help answer questions.
Injuneer is offline  
Old 02-04-2019, 03:06 PM
  #5  
Registered User
Thread Starter
 
Join Date: Aug 2000
Location: Folsom, Ca.
Posts: 108
Re: Starts and Runs Great When Cold Then....

10 months later......

New spark plugs, several Opti-sparks, MAF, coil, and it was running worse than ever. Went with the Torqhead LS Coil Conversion Kit TH-24XCVKW. Nice increase in h.p. but had intermittent stutter - like someone was turning the ignition key off and on for a split second (no codes and nothing on scanner) at mostly 2,000 to 3,000 rpm. The final solution was replacing the throttle position sensor.
Ken Cemo is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
thoreightysix
Fuel and Ignition
32
11-07-2013 11:13 PM
D'Z28
LT1 Based Engine Tech
20
01-16-2013 08:39 PM
Camaro90RS
LT1 Based Engine Tech
4
11-26-2008 07:56 PM
ssbowtie1
LT1 Based Engine Tech
22
04-12-2008 02:18 AM
CJ Black LS1 Z28 M6
LT1 Based Engine Tech
5
01-24-2003 09:06 PM


Thread Tools
Search this Thread
Quick Reply: Starts and Runs Great When Cold Then....


Contact 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.