khkchan

Hi I have a 1996 Accord EX 2.2L Vtec. Recently my CEL is on. OBD scans p0401 EGR flow insufficient code.

While being a novice, I went to an autoshop and they checked the EGR system. They said the EGR system is okay and the EGR valve needed to be changed because it doesn't hold vacuum. I paid for a new EGR valve. Couple miles after I left the shop, the CEL is on again.

I bought a Haynes manual and starts to learn the whole emission system. Given the EGR valve is new, the vacuum tubings to the valve are okay and the solenoid stuffs are functional, I start to check the MAP sensor. The 5V supply reads 4.98V. Here are the readings of the sensor wire:

Engine off Ignition on: 2.86V
After cold start: 0.99V (about 1000rpm)
At Idle speed: 0.90V (about 750rpm)
Almost floor the gas pedal: 2.53V (about 4500rpm)

Is the MAP sensor malfunction? After some internet search I believe the MAP sensor should read close to 5V with full throttle. Mine only go up to 2.53V.

Any help is greatly appreciated.

notoriousB

your MAP sensor will only read 5v if you have approximately 10-11 psi of POSITIVE pressure on it. If that were the case your car would be in limp mode. I believe anything above approx. 3v will cause the ECU to sense positive pressure, and since it's N/A the ECU will think something is very wrong.

So in short, your voltages seem correct. Your map sensor is fine.

Honda uses a 1.75 BAR MAP sensor, but any reading over 1 BAR (atmospheric pressure) is "bad" per the ECU.

I would look at the vacuum lines for the EGR system. They may have a tiny crack or pinhole in them which are causing your CEL.

HTH -B

khkchan

hi notoriousB,

Thanks very much for your response!

Now, I have checked the vacuum lines by applying vacuum from one side using the pump and measure the vacuum from the other side using the gauge. The lines seem okay.

I also did some EGR system diagnostics. When I apply 8 in-Hg vacuum to lift the EGR valve while engine is running (and already warmed to operating temperature), the engine did not stall as expected by the Hayes manual. I waited for about 30s and it still didn't stall. However, I did feel the engine temperature rises and fans came on.

I tested the EGR control solenoid by applying battery voltage. I heard the click sound and there was initially a 6.5 in-Hg vacuum on the vacuum line that connected to the EGR valve. Later it settled at about 7 in-Hg. Vacuum went away when I removed the battery voltage.

I tested the EGR Vacuum Control Valve by applying a 20 in-Hg on the vacuum input. On the vacuum output that connects to the EGR control solenoid, there is a 6.5 in-Hg vacuum initially and later it settled at around 7.2 in-Hg. Removal of the 20 in-Hg input, about 10 seconds later, the 7.2 in-Hg output disappears.

After some study of the vacuum control valve. I have a feeling that the vacuum control valve maybe bad. The engine is providing a vacuum source of about 21.8 in-Hg. Assuming atmospheric pressure 29.92 in-Hg, that should leave the EGR vacuum control valve to have an output vacuum of about 8.12 in-Hg when the ECU grounds the vacuum control valve. However, only about 6.5-7.2 in-Hg of vacuum output is observed on the EGR valve input.

Do you think this makes sense?


Modified by khkchan at 2:08 AM 6/16/2005


Modified by khkchan at 2:09 AM 6/16/2005

notoriousB

sounds like you've been doing your homework!

I am by no means an EGR system professional, emission components actually counteract what I'm trying to do w/ my car (LOL), but it sounds like your testing is right on. However I'm not sure that a difference of 1-1.5 in/hg in vacuum pressure is that big a deal, sounds like a very low discrepancy.

Also it's possible your calculations for atmospheric pressure could be slightly off due to elevation or perhaps even humidity. The true atmospheric pressure may not match exactly the theoretical calculation of atm. I think your problem may lie elsewhere, however as I said, I'm no EGR pro...

-B

Chiovnidca

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by khkchan &raquo;</TD></TR><TR><TD CLASS="quote">. However, only about 6.5-7.2 in-Hg of vacuum output is observed on the EGR valve input.

</TD></TR></TABLE>
If you hook your vacuum gauge up to the hose at the EGR valve, does it show vacuum when you raise the engine speed to about 2000 rpms? (the engine should be warm) If so, the EGR ports are probably clogged up.

khkchan

I am still learning the EGR system. What is exactly EGR ports? Do you mean the 2 holes that in on the EGR valve? If it is, since my EGR valve is new, I don't think it is clogged up. The EGR passage from the engine to the EGR valve maybe clogged up though. Since I don't have the service manual and don't know the exact torque required to tighten the EGR valve, I will treat removal of the EGR valve as a last resort.

If I understand it correctly, the ECU determines the amount of EGR flow by determining the sensor voltage from the EGR valve lift sensor. And with some conversion and comparison with the MAP sensor voltage, it will throw the p0401 EGR flow insufficient code. Since my EGR valve lift sensor is also new, I think the remaining reasons could only be an insufficient vacuum applied to the valve or a malfunctioning MAP sensor.

Maybe the ECU has more routines to determine EGR flow other than the EGR valve lift sensor.... don't really know. THis problem is getting tough.

Thanks all for your replies.

Chiovnidca

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by khkchan &raquo;</TD></TR><TR><TD CLASS="quote">I I think the remaining reasons could only be an insufficient vacuum applied to the valve or a malfunctioning MAP sensor.

</TD></TR></TABLE>
How about this check?

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">If you hook your vacuum gauge up to the hose at the EGR valve, does it show vacuum when you raise the engine speed to about 2000 rpms? (the engine should be warm) </TD></TR></TABLE>

deserthonda

insuficient egr flow as you stated......... most likely there is a restriction in the ports,i would remove valve and see if you notice any crap built up in ports

khkchan

Thanks all. I am convinced that it is due to the blocked EGR ports & passages. Honda has a service bulletin that address clogged EGR ports for 98-00 Accords and some amateur site claims that it affects all Accords since 1990. Also, when I lift the EGR valve, the observation that the engine didn't stall prove that it is the EGR ports and passages.

It looks like that accessing the EGR ports is quite involved: removal of the accelator cable, air intake, coolant hoses, etc etc. I am wondering if spraying carb cleaner into the hole under the EGR valve will help.

thanks.

Chiovnidca

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by khkchan &raquo;</TD></TR><TR><TD CLASS="quote">when I lift the EGR valve, the observation that the engine didn't stall prove that it is the EGR ports and passages.

</TD></TR></TABLE>
That's a pretty good indication.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by khkchan &raquo;</TD></TR><TR><TD CLASS="quote">
I am wondering if spraying carb cleaner into the hole under the EGR valve will help.
</TD></TR></TABLE>
That's not very likely to help, you usully have to dig all the crud out.

Qfactor

just take out the 10mm bolts that hold the plate on your intake manifold just behind the injectors and get yourself a can of some good carb cleaner and a engine cleaning brush....such as this one's

http://www.sdpc2000.com/images...2.jpg

once you clean this apply vacuum to the egr and should stall the engine.

BTW: your year accord is covered to 150K miles under the Emission Warranty Extension, you could do this on your own and pay out of pocket or take it to your Honda dealer and get it done for free... and maybe Honda can re-inburse you for the egr (if it is Honda OEM part).

khkchan

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Qfactor &raquo;</TD></TR><TR><TD CLASS="quote">just take out the 10mm bolts that hold the plate on your intake manifold just behind the injectors and get yourself a can of some good carb cleaner and a engine cleaning brush....such as this one's

http://www.sdpc2000.com/images...2.jpg

once you clean this apply vacuum to the egr and should stall the engine.

BTW: your year accord is covered to 150K miles under the Emission Warranty Extension, you could do this on your own and pay out of pocket or take it to your Honda dealer and get it done for free... and maybe Honda can re-inburse you for the egr (if it is Honda OEM part).</TD></TR></TABLE>

I currently reside in California but my vehicle was originally purchased in Ontario, Canada. They called it EX-R and it is equivalent to the US EX version. Yes, my car is in metrics.

I don't think there is any extended emission warranty for 95-97 vehicle that was originally purchased in Canada (I called Honda Canada and confirmed on this). I have tried to call Honda America.. one agent said that my VIN is wrong, the other said that there is no extended emission warranty for my vehicle.

Do you think the emission warranty settlement with EPA applies to owner who purchased his/her vehicle outside US and currently resides in US?

I will try to see if I can access the 10mm bolts without removing the fuel rail.

Thanks for your reply.

Chiovnidca

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by khkchan &raquo;</TD></TR><TR><TD CLASS="quote">

Do you think the emission warranty settlement with EPA applies to owner who purchased his/her vehicle outside US and currently resides in US?

</TD></TR></TABLE>
No.

Qfactor

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">
No.</TD></TR></TABLE>

sorry mate, on your Canadian Accord


Thanks..Chiovnidca.

mikework

Honda accord 1996 2.2 EGR problems the vacuum lines are not pluged and egr ports.The solenoid gives vacuum to the EGR but stays even at idle there is vacuum about 7 in hg vacuum presher dose not go away engine and stalls.

doctorbee

please start a new thread.