Forum: C4 ZR-1 Technical Postings
3 Weeks Ago
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Replies: 21
Views: 4,658
Re: Poor running
Could be related to the crankshaft sensor, injectors and/or Engine Computer (ECM).
Code 42 means the ECM is in Bypass Mode, during which spark-timing is controlled by the DIS and not the ECM....
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Forum: C4 ZR-1 Technical Postings
03-31-2025
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Replies: 18
Views: 13,824
Re: Crank No-Start/Idle 91 ZR-1
I can confirm, I have been able to repair almost every C4 Corvette ZR1 ECM I've worked on. The few that are not repairable I strip for parts.
Based on the numbers, there are 10-15 ECM failures...
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Forum: C4 ZR-1 Technical Postings
10-03-2024
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Replies: 42
Views: 20,367
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Forum: C4 ZR-1 Technical Postings
09-27-2020
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Replies: 42
Views: 20,367
Re: ECM Issues - No Start
Just an update to provide this link on troubleshooting the C4-ZR1-ECM:
http://zr1ecm.com/youfix.html
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Forum: C4 ZR-1 Technical Postings
09-27-2020
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Replies: 7
Views: 1,889
Re: Crank but no start
As the C4-ZR1's reach 30 years old, this is becoming a common issue. I prepared a few web pages that provide useful tips on how to diagnose a no-start issue.
http://zr1ecm.com/youfix.html
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Forum: C4 ZR-1 Technical Postings
08-07-2020
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Replies: 137
Views: 28,503
Re: 93 Starter Not Engaging
Just thought I would chime in for those experiencing strange starting issues.
Some years back I discovered the clutch-lock-out switch was troublesome by design.
The clutch switch forces the...
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Forum: C4 ZR-1 Technical Postings
08-02-2020
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Replies: 170
Views: 35,617
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Forum: C4 ZR-1 Technical Postings
08-01-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
Tripler - it sounds like you narrowed it down to an ignition issue. Once you replace the coils and reassemble the plenum, you'll be able to test.
Coils that are not providing adequate voltage are...
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Forum: C4 ZR-1 Technical Postings
07-31-2020
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Replies: 170
Views: 35,617
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Forum: C4 ZR-1 Technical Postings
07-24-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
Yes, good idea to change the ignition coils and perhaps the hi-tension leads while you have the plenum off.
The coils are all the same so if you want to test for the sake of testing you could...
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Forum: C4 ZR-1 Technical Postings
07-23-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
Yup sounds like it - unless the Hi-Tension lead going to #8 is the issue. Perhaps the lead is creating high resistance or shorting to ground.
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Forum: C4 ZR-1 Technical Postings
07-22-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
To double check, start and run the engine with 5 and 8 disconnected. Connect 5 and note any changes in idle. Connect 8 and note any changes in idle.
If connecting 5 and 8 didn't have any...
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Forum: C4 ZR-1 Technical Postings
07-22-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
Tripler - sounds like cylinder #8 is off-line. Its waste-spark partner is cylinder #5, so try the test by removing that Hi-Tension lead to see if doing so has any affect.
If #5 and #8, together...
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Forum: C4 ZR-1 Technical Postings
07-20-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
ZR2 and Tripler - We gotta do process of elimination to narrow it down.
ZR2 - If you suspect it is a plug issue, you might want to remove one plug wire at a time and run the engine to isolate...
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Forum: C4 ZR-1 Technical Postings
07-18-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
Sounds like a cylinder or two are off-line. Any fault codes?
Verfiy the ignition leads as detailed in this thread. Afterwards, you will need to verify your injectors and/or the (-) feed to the...
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Forum: C4 ZR-1 Technical Postings
07-18-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
Hmmm.....One cylinder could be off line due to fuel starvation. It could be an ECM issue since you've already changed the injectors.
After ruling out your ignition system by checking the...
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Forum: C4 ZR-1 Technical Postings
07-18-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
To check plug wires:
Method 1 is to use an inline spark plug tester. Test one lead at a time. Connect one end to the incoming HI-Tension lead, the other to GND (normally the other lead goes to...
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Forum: C4 ZR-1 Technical Postings
07-16-2020
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Replies: 170
Views: 35,617
Re: Ruff Idle ,Huge Loss of Power
I'm interested in hearing the engine to determine if all 8 cylinders are firing.
Did you verify that each HI-TENSION lead is providing a signal to its matching plug?
For example, if one coil is...
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Forum: C4 ZR-1 Technical Postings
07-14-2020
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Replies: 170
Views: 35,617
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Forum: C4 ZR-1 Technical Postings
07-09-2020
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Replies: 31
Views: 27,842
Re: Long cranking
I didn't like the original factory start-up procedure because it takes far too many cranks before the engine starts. This is due to the ECM delaying fuel delivery.
When the engine is turning...
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Forum: C4 ZR-1 Technical Postings
07-07-2020
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Replies: 17
Views: 2,759
Primary Fan Runs When ignition in "ON" position
That's a good sign. It suggests to me the ECM is capable of controlling its (-) output to the primary fan relay on circuit 409, pin 6 of Green Connector (C6).
Could it be you have a Code 14, 15,...
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Forum: C4 ZR-1 Technical Postings
07-06-2020
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Replies: 17
Views: 2,759
Re: Fans on when ignition in accessory position
I'm thinking the primary cooling fan is "controlled by the ECM" thru the Green Connector "C6". This provides a (-) signal to th Primary Fan Relay.
If you disconnect the Green Connector and turn...
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Forum: C4 ZR-1 Technical Postings
07-05-2020
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Replies: 2
Views: 1,363
Re: Test injector pulse
It is possible to test your ECM's ability to activate the injectors with the plenum removed but if the Ignition Module is removed you will not get any injection pulses while cranking the engine over....
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Forum: C4 ZR-1 Technical Postings
07-03-2020
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Replies: 42
Views: 20,367
Re: ECM Issues - No Start
In actual fact, the ECM does not have an input for oil pressure. I guess it wasn't a consideration for software control back then.
I find the the LT5 pressurizes its oil very quickly when cold...
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Forum: C4 ZR-1 Technical Postings
07-03-2020
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Replies: 42
Views: 20,367
Re: ECM Issues - No Start
The stock ECM provides an injection delay of 1 or 2 seconds, which is not nearly enough time to prime oil into the LT5 engine. My inclination is that it would take closer to 30 seconds to prime and...
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