Compression Spec?
#21
03-31-2011, 09:04 AM
We had a Cougar XR7 with the 4.6 V8. It had the off idle stubble when you would blip the throttle, but on the road it was barely noticeable. It was a problem with the EGR system. The port was full of carbon. You would take off the EGR valve and see if the port is fully open. To clean it you would need to use a drill bit the approx size the hole is and have a shop vac removing the carbon as you chip away.
I was checking into how the cams advance and retard in your engine. It appears the cams are in the retard position at idle and at high load/speed. Is is possible to disconnect the advance units to prove they are working properly? Like checking for a cylinder misfire, when you disconnect the offender, nothing happens.
I was checking into how the cams advance and retard in your engine. It appears the cams are in the retard position at idle and at high load/speed. Is is possible to disconnect the advance units to prove they are working properly? Like checking for a cylinder misfire, when you disconnect the offender, nothing happens.
#22
03-31-2011, 09:26 PM
I get what you are saying about EGR and that these engines use the VVT to change cam overlap thus allowing more or less exhaust gases to mix with the incoming air/fuel mixture.
If I understand it correctly the solenoid is energized and then oil pressure is fed to the VVT and it advances the Cam. When it's advanced is when there is more exhaust gas mixing with the intake air. In order for EGR to continue at idle, a VVT or solenoid would have to get stuck in the advanced position.
In my case the problem is mainly at freeway speed under light acceleration and only very rarely at Idle.
I'll look into running with the vvt's unplugged. I expect that I'll definitely get a CEL then.
If I understand it correctly the solenoid is energized and then oil pressure is fed to the VVT and it advances the Cam. When it's advanced is when there is more exhaust gas mixing with the intake air. In order for EGR to continue at idle, a VVT or solenoid would have to get stuck in the advanced position.
In my case the problem is mainly at freeway speed under light acceleration and only very rarely at Idle.
I'll look into running with the vvt's unplugged. I expect that I'll definitely get a CEL then.
Last edited by Sinister 1; 03-31-2011 at 09:28 PM.
#23
04-25-2011, 09:01 AM
Marc,
I'm chasing a random miss also. Mine is at part throttle acceleration and very occasionally at idle. Oh yes and it's very intermittent.
For example, I drove the car 408 miles last Thursday without an issue until the last 20 miles. All of the driving was freeway then all of the sudden it starts acting up for no reason.
The stumble happens mainly under part throttle acceleration when the engine is "pulling the load". I've plugged the OBDII reader in so many times I'm going to wear out the connector. No codes at all. I'm at my wits end and am about to start changing parts (which I deplore) just to see if the issue goes away.
I've been through all of the diagnosis and at this point all I can think of is it's not a "Miss" but a Lean Stumble instead. I'm going to get my injectors cleaned in the next few days and see if that helps.
I'm chasing a random miss also. Mine is at part throttle acceleration and very occasionally at idle. Oh yes and it's very intermittent.
For example, I drove the car 408 miles last Thursday without an issue until the last 20 miles. All of the driving was freeway then all of the sudden it starts acting up for no reason.
The stumble happens mainly under part throttle acceleration when the engine is "pulling the load". I've plugged the OBDII reader in so many times I'm going to wear out the connector. No codes at all. I'm at my wits end and am about to start changing parts (which I deplore) just to see if the issue goes away.
I've been through all of the diagnosis and at this point all I can think of is it's not a "Miss" but a Lean Stumble instead. I'm going to get my injectors cleaned in the next few days and see if that helps.
I kept the old coils from the last time I changed them all. With the confusion about cylinder numbering, I took a shot in the dark and replaced the middle coil on the left bank. That is actually #5, hahaha. I then had to pull that dreaded intake system to change the real #2. Car is running fine now. I also learned that you have to zip tie the connectors to make sure of the connection.
#25
04-25-2011, 07:44 PM
Veteran Member
#26
04-25-2011, 09:10 PM
The specs for the basic engine are the same for AJ26 and AJ27. Both the VVT's are "two position", so to speak, the AJ27 is just infinitely variable and the AJ26 is on-off. In practice the cranking compression pressures are also basically identical, even with different ratios.
For all intents and purposes, all the differences between the two are external controls and sensing.
Cheers,
For all intents and purposes, all the differences between the two are external controls and sensing.
Cheers,
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