What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Explain this one... Technicians check in... (small update at end)

sled_dog

sled_dog

1 ton status
Joined
Sep 3, 2002
Posts
16,867
Reaction score
3
Location
Austin, TX
Sorry for the length of this.

OK my 350 Vortec has had both banks running rich for quite a while. I put 2 upstream O2 sensors in it over a year ago(my attempt to fix it then). When it went through emissions the mechanic doing it put a Fuel Pressure Regulator in it and the Rich COndition seemed to have gone away and it passed emissions. Now a year later, the condition has been back for a little while, it gets bad mileage(about 11) so it is in fact running rich. The code is mildly intermittent(light goes on and off so its passing plenty of drive cycles obviouslly). It went off long enough once that I got it through emissions this year, including the required sniffer test. Then the codes came back. Finally a guy at work gave me a spare Mass Air flow he had. It was replaced because the truck ran like crap when it was cold, but it never tripped a code. So I put it on figuring, long shot but why not try it. Sure enough, 3 weeks of using the MAF, it ran like crap cold but the Rich code was gone. So I confirmed on Monday there were no pending or stored codes and ordered a brand new Mass Air from a local Chevy dealer(AC Delco, no aftermarket crap). I installed it today, the truck isn't making the MAX power it has ever, according to the old seat of the pants dyno, but I didn't care as long as the codes were gone. Well, tonight they both came back(P0175, P0173, Too Rich on both banks).

Now, this isn't asking how to fix the rich condition, but can someone explain why the hell the other Mass Air Flow didn't let the codes come up? Now if you want to take a crack at "fixing" the problem, be my guest.
 
Well, I can only go by the info you put in your post. I am sure if you tried to post every liitle thing done on this engine (especiely if it where an early LT type small block to vortec small block engine swap), you would have to write a book.

You said that the swapped in MAF stopped the codes from coming back, but I do not think it did because after installing the new MAF you bought, they came back any way. You did mention that the smog tech installed a temporary fuel pressure regulator, which caused the engine to lean out, and pass smog. This leads me to think he lowered the pressure, in order for it to lean out, which could mean that your fuel pressure may be too high. Excesive fuel pressure is somthing an ECM cannot over come and compesate for. If you have done some modifications to your Fuel injection system, in order to run a higher performance engine, then the problem could be ecesively high fuel pressure. This is just a guess taken from the info you posted.
 
Sorry, this is my 97 C2500, DD and Tow Rig. Only mods are removing factory things that reduced air flow in the intake(not manifold but air cleaner).

The Fuel Pressure Regulator was INSTALLED. Not temporarily. THe Check Engine light was gone for almost a year. I've only tested Fuel pressure, not running. Turn the key on, build pressure, reads within spec. I am going to try and get some time to test fuel pressure under running conditions tomorrow.
 
Rich both banks means that it can't lean it out enough to make it switch to lean. You'll be most likely looking for a fuel related concern. My guess is that the poppet valves and/or the fuel injectors are hanging up some. GM had problems with this. They recommend running the injectors off of a mix of top engine cleaner to gasoline for a while. The proportion is 1/4 top engine cleaner, 3/4 gasoline. You need to disable the fuel pump relay and devise some kind of way to not return fuel to the tank, and pressurize the fuel rails. GM has the proper tools for this. It's a little block that attaches where the fuel lines go in, and also has a little pressure chamber that allows you to pressurize the fuel to run into the injectors. Do not let the top engine cleaner back into the tank, or pour it directly in the tank. Big problems.

Second guess is partially or fully clogged cats. Wont let the exhaust out, and fools the O2 sensors into thinking that it is running rich, which cuts more fuel, makes the cats hotter, which contributes to more cat melting. Can check the cats with an infrared thermometer. The rear of the cat should be approximately 100 degrees F hotter than the front of the cats. Hot up front means the cats are plugged.

That will get you started.
 
thanks, never knew to test a cat like that.

I read a TSB about cleaning the poppets but wasn't surea bout it. We have a BG service that runs the engine off of their cleaner, disable the pump, hook up an air line and lower the pressure so it doesn't return to the tank. Maybe I will go get some top engine cleaner and pinch the return hose, give it a run see if it helps.
 
Is the ECM sensing engine temp right? Running like crap cold and then rich when warm, bad economy, it could be a possibility. Assuming you've got a scanner to see this though.

Bad connectors/wiring can also make codes go away temporarily when parts are swapped.
 
I know what you mean. When warm it seems to be sensing temperature correctly. It always slipped my mind to look and see if the ECT was reading properly when the truck is cold, I will try and take a look at it today. My Saturn got crap for gas mileage and ran WAY rich and that was an ECT.
 
Coolent temp sensor?

Have you checked this?

Sometimes they read low and don't trip a code.
 
AllData has been out of comission at work. SO I'm having trouble locating Resistance/Temperature charts. Datastream read fine at idle and seems to at temperature as well. For the freaking price maybe I'll get one and see hwat ti does if they don't fix AllData soon.
 
update

OK so I finally did an injector balance test. Today at work I checked the resistance of the ECT. According to the Haynes manual I have(AllData is still down at work) the sensor is within spec. Now one thing I noted, I checked reference voltage, with key on engine off, the voltage coming into the sensor was something like 3.2V. Should be 5V as far as I know. I used my crappy Craftsman meter(getting a new one next week), so I will check with someone elses tomorrow. Thinking maybe I have some reistance in the power wire between the pcm and the sensor. Need AllData so I can figure otu which wire at the PCM is the ECT wire to check its resistance.

But anyway, I did an Injector Balance test tonight. A friend works night shift at a GMC dealer so he hooked up his pressure gauge and a Tech II tonight. All of the injectors tested just fine. As I had already figured out, fuel pressure tests just fine. I did a BG fuel injection service at work today. Which did nothing to help it, figured it was worth a shot. So now I'm scratching my head and I guess hoping its that reference wire to the ECT. Anyone run into this before? If its that wire, I'm just going to get some yellow wire(same color) and overlay a new damn wire from the PCM to the sensor and call it good.
 
One problem I have seen with these is the fuel pressure regulator leaking fuel into the manifold, causing a rich condition, hard starting, bad fuel mileage, etc. Normally, the fuel pressure will still test OK. I've replaced two regulators in two different vehicles because of this.
 
it was replaced a year ago. Not that I don't think it could go bad in that amount of time of course. How would it hold pressure if its in fact leaking down into the manifold? Pressure was 60psi running, 51 just sitting there. It would spike to 65 then slowly creep on down to 51 and stay constant there.
 
sled_dog said:
it was replaced a year ago. Not that I don't think it could go bad in that amount of time of course. How would it hold pressure if its in fact leaking down into the manifold? Pressure was 60psi running, 51 just sitting there. It would spike to 65 then slowly creep on down to 51 and stay constant there.
Click to expand...

I must've missed that. :doah: Actually, I'm not sure if it leaks on the inlet or the outlet side. If they leak on the inlet side, then they could still hold pressure. I'll try to remember to ask my friend if his held pressure when it leaked.
 
You must log in or register to reply here.

Latest Posts

Top Bottom