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Intermittent code 51; WTF???
Topic Started: Oct 21 2013, 05:45 PM (785 Views)
truckjohn


Hey guys,

'94 3-cyl with upgraded emissions

Been trying to sort out this intermittent code 51 - EGR system.... I can reset the codes - and it will throw the code maybe 3 or so days later..... Doesn't sound like much - but I am driving a bunch.... it's like throwing the code 1x per 450 miles....

So.. I checked the physical system... Appears to be working ok...
EGR sol ohms about right... 33-39 ohms... Sometimes it ohms 40 ohms - then back to 37.5... Certainly not an open....

Cleaned out the EGR itself... It is nice and free....

What am I missing here... Why would it throw the codes once in a while?

Thanks
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Deleted User
Deleted User

I've had to clean out the modulator valve to get the code to go away. The cap will come off. Just make sure you mark the "P" and "Q" on the modulator valve case when you take off the cover. There's a little filter in there. Soap and hot water on the filter. Blot it dry and let is sit for a while. I toss the rest in the ultrasonic cleaner. I'm not sure how else to do it. Perhaps, soaking in Purple Power or something for a while?
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00Metro
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Unclog the passages in the intake and head.
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David95237


Did you check the passages?
Edited by David95237, Oct 21 2013, 08:26 PM.
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truckjohn


I cleaned all the passages in the head, intake, and exhaust manifolds when I did the head work a month ago...

Gonna try to disassemble Mr. Modulator and see what I can do there....

Thanks
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MarkyMayhem


I replaced the modulator with a junkyard one. Every 3000 or so miles I reset the ECU. every once in a while I clean it out. I have a 4cyl, and to be honest, when I get a code 51 [95 upgraded emissions, OBDI] I don't have ANY mpg, perfomance etc issues. I just reset and roll. My head-side passage is clean, exhaust side.. maybe sorta.

-m

ps - 200k and the motor will be the LAST thing to go - in to my ultralight!!
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MarkyMayhem


PS there IS a bolt broken off aon my EGR, and a good glob of black RTV everywhere a leak could be around the EGR but... egh... not the best a) seal b) EGR c) passages. but heck, she runs like a champ
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clarkdw


The code is triggered by the change in vacuum reading caused by the EGR opening as seen by the MAP sensor. If there is not enough change in the MAP voltage when the EGR valve is test fired by the ECM it sets the code. Leaky vac hoses? Leaky throttle body gasket? There could be a number of suspects.

I created my own code 51 by adding a reservoir bottle on the vac line to the MAP sensor where I have my vac gauge hooked up. The MAP/ECM is very sensitive and the actual change in vac is very small so it doesn't take much to set the code. If I keep my accumulator bottle smaller than 1/2 a pint it generally will tolerate that.
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truckjohn


So... I cleaned out the modulator at lunch... Reset the CEL - and within 15 minutes of driving, it was back....
Perhaps at least what ever is going on - it's more consistent.... which would make it much easier to track down....

I did have a peek around - I see some cracks on the brake booster vac lines... Gonna replace those and probably go ahead and get 10 ft of vac hose and just replace everything..... Gotta go dig up my vacuum pumper thingey - verify that the brake booster holds vacuum.... When I hit the brakes - the engine idles horrible....

Something I did notice... When I turn the key - I don't hear the fuel pump run up... Even though I get fuel.... Last time that happened - it was the fuel filter full of crud.... 3 weeks ago.... I am going to pull the fuel filter tonight... If it's clogged - I am ordering a new tank....

Thanks
Edited by truckjohn, Oct 22 2013, 01:26 PM.
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Deleted User
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Mythstae's EGR system had the worst black goo from hell that I have ever seen, especially in the passage through to under the throttle body. It took two times cleaning it to get it to where it wouldn't throw a code.

By all means, get a new fuel tank. ^o) One "E-D-B-D" little piece of anything that gets past the fuel filter will lodge in your fuel injector, and you'll be walking.
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truckjohn


I cleaned out the EGR passages in the intake real good with a bottle brush and carb cleaner...
I checked and cleaned the original modulator - but it wouldn't operate right.. Replaced it with new...
The one from Napa is a genuine Denso unit... Could very well be old GM/Suzuki inventory.....

Anyway - this morning... Drive to work.. NO Check Engine light... We will see - but I am cautiously optimistic....

On to the next thing...

Thanks
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