P0401

[snakebit]

About 300 mi on the new coldside and I just got P0401, insufficient EGR flow. Any ideas? All the posts at miata.net refer to cleaning the stock intake manifold.

[Mx5-4me]

About 300 mi on the new coldside and I just got P0401, insufficient EGR flow. Any ideas? All the posts at miata.net refer to cleaning the stock intake manifold.

That should be easy it's prolly sittin' on shelf in your garage...

:party:

[snakebit]

That should be easy it's prolly sittin' on shelf in your garage...

:party:Oh, go get blown . . . .;)

[tann3r]

Theres not too much to check, you have the EGR pipe from the header to the EGR valve, then the small bit of piping from the EGR valve to the throttle body adapter manifold. Make sure there are no sharp bends in teh pipes or anything stuck in them. Ive never heard of an egr valve failing, but i think that would throw a cel of its own.

[ScottA]

I noticed on my install that the little stainless steel tube that conects the EGR adapter plate to the SC manifold was slightly restricted from being cut with a tube cutter. " the ends are slightly crushed in ". It is possiable to open them up a little by countersinking the ends with a slightly larger drill bit.
Just an observation 7 my 2cents.

[Mx5-4me]

Oh, go get blown . . . .;)

Believe me, i'm tryin' !!!

[Tom @ Fast Forward]

A vacuum leak can also do it. Make sure the vacuum line from the "boost" solenoid on the passenger fender is connected securely at the VDB and that all VDB connections are tight. Last but not least, as was mentioned, some EGR SS tubes got out with the tips restricted. That problem has been cured for quite awhile but yours might be one of those. Pulle the tube and look at the ends. Open the ends if necessary.

[snakebit]

A vacuum leak can also do it. Make sure the vacuum line from the "boost" solenoid on the passenger fender is connected securely at the VDB and that all VDB connections are tight. Last but not least, as was mentioned, some EGR SS tubes got out with the tips restricted. That problem has been cured for quite awhile but yours might be one of those. Pulle the tube and look at the ends. Open the ends if necessary.Tom, your accuracy is almost creepy.:ninja:
The vac line to the boost solenoid was on, but no clip and kind of loose.
The EGR tube was a bit restricted at the tips.
You were also dead-on about the leak at my boost gauge.

I'm beginning to wonder if this supercharger business is just a front for field testing some new micro vid cam that is mounted somewhere on the kit. Tom activates the cam remotely and sees exactly what's going on underhood.:shifty:

[Tom @ Fast Forward]

I am omniscient. ;)

[ThomS]

Ok what could cause this Code to pop up when it never has before. All vacuum hose have been checked and all seem to be tight.
Seems to be no vacuum leak. This kit has been on this car for three years, right Tom. So it shouldn't have anything to do with EGR tubes ? Oh and it only did it once and not since, at least 300 more miles.

So any ideas why this code showed up. P0401

[Tom @ Fast Forward]

Either the small stainless tube from the EGR assembly is restricted (carboned up) or there is a small leak at the VDB or one of the hoses to the VDB. Those would be my two guesses.

[ThomS]

I checked the vacuum hoses but maybe I will just replace them to be sure, and I will check the EGR assembly today,
Would this code come very intermittingly ?

All I have read there seems to be no other cause for this code, is that true ?

[Tom @ Fast Forward]

I don't think you need to change the hoses, just inspect them carefully. They don't tend to go bad.

What vacuum are you getting at idle?

Pop off the tube from the EGR assembly to the BTB adaptor. See if it is full of carbon.

[ThomS]

I will do the EGR tube as son as I can. Its not easy to get to with my big hands.

At idle the vacuum is 18 to 20 points.


My question is, does this code come very intermittingly ? Like once then not again for say over 500 miles?

[Tom @ Fast Forward]

Vacuum sounds good. If you have a test vacuum gauge, it would be interesting what it reads right at the VDB.

Yes, I would think the EGR error would be random.

[ThomS]

Vacuum sounds good. If you have a test vacuum gauge, it would be interesting what it reads right at the VDB.

Yes, I would think the EGR error would be random.


Yes I have a test vacuum gauge. Remember we bought it when you were out last trip, I forget but we needed the info for something. After that I had the boost and A/F gauge installed.

[ThomS]

Vacuum sounds good. If you have a test vacuum gauge, it would be interesting what it reads right at the VDB.

Yes, I would think the EGR error would be random.

Ok put on the test vacuum gauge on the spare outlet on the VDB and when I started the car it was around 10 points after the car warmed up it went to 17 to 18 points.
Now the cap I had on the spare did have a few stress cracks but not bad.
Put on a new one.

[Tom @ Fast Forward]

I guess the question is, does that vacuum gauge and your normal gauge attached directly to the manifold agree at cold start. Let it sit over night and start it and watch both gauges. If the VDB gauge does what you said above and the the manifold gauge is 18-20 even cold, that pretty well answers the question.

[ThomS]

I guess the question is, does that vacuum gauge and your normal gauge attached directly to the manifold agree at cold start. Let it sit over night and start it and watch both gauges. If the VDB gauge does what you said above and the the manifold gauge is 18-20 even cold, that pretty well answers the question.

I guess the answer is that at cold start the VDB says 10 points and the attached gauge says 18 points, as thye car warms up they become the same numbers. I did this at cold start. But will do it again.

If all stays the same then, what is my answer ?

[Tom @ Fast Forward]

Thatconfirms that you have a leak at the VDB or one of it's hoses that goes away when it warms up.

[ThomS]

The second test and it stayed the same 10 points until it warmed up.

Cleand up all the hoses that came from the VDB and tightened all them up, and the results came out the same. W/ temporary gauge 10 points cold and 17 to 18 points when warmed up and the permanent gauge is 18 points all the time.

[Tom @ Fast Forward]

Could your EGR tube from the EGR valve to the BTB adaptor be broken? Is yours Stainless or one of the very early copper tubes?

[ThomS]

Stainless steel and looks ok. I haven't taken it off yet, but soon. You know me Tom it takes me awhile to get up the nerve to work on somethings.

If I do not find the cause can this become a bigger problem on the trip ?

[Tom @ Fast Forward]

That is a nuissance code and of little issue. In the pursuit of science, I have removed my EGR all together and get that code from time to time. "EGR LOW FLOW". LOL, I guess zero flow is "low"? :)

[ThomS]

Well the next thing is to remove the EGR tube and check it, if that is ok whats next ?

[Tom @ Fast Forward]

Next would be the other ends of the hoses and the hoses themselves coming from the VDB.

Another thought that comes to mind could be the PCV valve, but not likely.

[ThomS]

Cleaned up the other end of the hoses and inspected the hoses and all look good. Put it all back together and same thing. I could replace the hoses but don't think that is needed, but ???????????

[Tom @ Fast Forward]

Well, I guess I would start plugging off the ports on the VDB one at a time until I plugged one and the problem went away. Don't drive it like this but I would start with the hose to the brake boost canister. Let me repeat, DO NOT DRIVE IT WITH THAT HOSE BLANKED OFF. could be a problem there.

Are the bolts holding the BTB adaptor to the blower and the BTB to the adaptor tight?

[ThomS]

Well, I guess I would start plugging off the ports on the VDB one at a time until I plugged one and the problem went away. Don't drive it like this but I would start with the hose to the brake boost canister. Let me repeat, DO NOT DRIVE IT WITH THAT HOSE BLANKED OFF. could be a problem there.

Are the bolts holding the BTB adaptor to the blower and the BTB to the adaptor tight?


Yes The BTB adaptor and the adaoptor to the blower are all tight. Haven't had time to check out the other yet.

[Tom @ Fast Forward]

Well, at idle, the only thing that separates the intake manifold from the VDB is the short hose from the BTB adaptor to the VDB. They should be the same unless there is vacuum loss at the VDB.

Ah, one more thought. Start it up cold and watch the bypass valve on the side of the supercharger. See if it takes a few seconds to actuate. Could be it is sticking. In which case the vacuum in the VDB will be higher than the vacuum in the Intake Manifold. Good possibility?

[ThomS]

Well, I guess I would start plugging off the ports on the VDB one at a time until I plugged one and the problem went away. Don't drive it like this but I would start with the hose to the brake boost canister. Let me repeat, DO NOT DRIVE IT WITH THAT HOSE BLANKED OFF. could be a problem there.

Are the bolts holding the BTB adaptor to the blower and the BTB to the adaptor tight?


I will be doing the test tonight for the vacuum hoses, Do I have to start the car for the test and when I get the results shut the car down before I move on to the next one or can the car stay running ?
I will not drive the car this way, just idle in the drive way.

Sorry it has taken awhile to do this work has kept me real busy.

[Tom @ Fast Forward]

If it is warm, you don't have the problem, right? You may need to work fast to find it. Sadly, I envision one or two hose tests each day with the engine cold.

Main test is to see if cold, the bypass operates freely. You can possibly test it cold by hand with the engine off.

[ThomS]

If it is warm, you don't have the problem, right? You may need to work fast to find it. Sadly, I envision one or two hose tests each day with the engine cold.

Main test is to see if cold, the bypass operates freely. You can possibly test it cold by hand with the engine off.

The vacuum test shows that the pressure is low at the VDB when cold and seems to go away as it get warm, YES.

The P0401 code came on after I had been driving for about an hour.

Do I have to start the car for the test and when I get the results shut the car down before I move on to the next one or can the car stay running ? If so the test may take two or three days. ?