Alright, to quickly recap the situation again for those who might not have read it on my first two posts, obviously the car is running lean. Ever since I put the car back together from my last oil leak attempt it is running lean. My A/F gauge reads lean at idle. It tends to favor lean when it's cruising, and it does not go rich at WOT like it used to. It also doesn't want to idle correctly when it's in open loop mode. I confirmed that my A/F gauge isn't just making up the lean reading because my plugs are very much white.

I was told to check the vacuum, it reads 13 inches at idle, which strikes me as a little low. A friend has a stock Z-28 that pulls 20 at idle. I know my cam gives up some, but I didn't think it would be that low. I tried the carb cleaner trick, spraying it around the intake, around the injectors, etc. Nothing changes the way the car idles.

Yesterday I removed the intake, took 2 hours to carefully remove ALL of the powder coating overspray on all of the mating surfaces and re-assembled it with new gaskets. No love, same situation. I thought perhaps that it was a vacuum leak, so I have individually capped ALL of the vacuum ports on the intake until there is no opening but the throttle body. It still only pulls around 12 to 13 pounds of vacuum at idle. Same conditions under throttle, in no way does it ever begin to go rich, even with the fuel pressure way up because the vacuum line is removed.

The only thing as such that I hadn't been able to try was perhaps my injectors, or the injector O rings, even though the carb cleaner test didn't net any results. I called up a friend and borrowed his 36 pound injectors. I knew that this would be WAY too rich but at least I could see if the O rings had cured the vacuum problem.

I put them in there and fired it up. It immediately died, so I fired it back up with some throttle this time and played with it until it learned how to idle with it's new injectors. Well, it's no longer reading lean at idle, in fact it reads perfect, and didn't move. I assume that it just had to trim the pulse width to minimum and keep it there just so it would idle. Anyway, I drove it like this and it was terrible as expected. Any harsh throttle movements and it would immediately stumble and buck. The thing is that my gauge still never read on the rich side. Vacuum was still around13.

So with the large injectors in there it made me think that maybe my less than 6 month old O2 sensors might be the problem since it never ran rich even when I know it should have. However, that still doesn't explain my two main problems of it running leaner than it should on a cold idle or at WOT where it should ignore the sensors anyway.

Even if my sensor is screwed up, it seems like my problems are exactly backwards of what it should be. If the sensors were screwed it should run at idle and at WOT, but not correctly at cruising. And that still wouldn't explain the low vacuum. Of course that assumes that this vacuum really is low.

Oh, one more thing. Yesterday I put my vacuum gauge on a friend of mine's Z-28 with a hot cam. His read around 14 inches, but he said he is pretty sure he has a vacuum leak because his A/C and stuff shifts around when he hits the gas. So yeah, my vaccum is close to his, but he's pretty sure he's got a leak so what does that really tell me?

I'm just about ready to drive my car off of a cliff.


[Modified by Nathan Plemons, 9:18 PM 7/19/2002]

 

don't drive it off the cliff... geez...

O2 sensors???

 

Hey Nathan,
Suxs to hear its still happening!!
Gotta be frustrating I bet.You seemed to have tried all the obvious things to do.

All I can think of now is to use a scanner and take it from there.If you ARE running lean,the scanner will show that,plus your 02 volts,Block learn and integrator,fuel injector pulse width, etc.

Usually,when a car runs lean,the O2 sensors can pick this up and make it run richer.Since your plugs are white and the gauge is telling you lean,the ECM may be fooled or being told its running rich so it leans the fuel out,OR,false air getting in the system and the ECM isnt picking it up and its running leaner in there.Is the motor pinging by an chance?

Also, vacuum for a 350 TPI or EFI engine should be between 17-21 inches of vacuum,Any lower is usually a vacuum leak.
You already knew this and mentioned your friends car pulled 21.Yours being so low down to 13,somethings amiss there.I agree the cam alone wouldnt knock it down so much.DId you make any changes to the system when swapping intakes?

Anyways,I mentioned this before but not sure if you got in the other post,If you need to use a scanner,let me know.

I have a snap on scanner and can use it on GM cars up to 1993 and could help you out with it if needed.So let me know if you can use it if no other ideas or options are left.Sometimes the scanner can show you whats wrong,sometimes it cant.

Good Luck and let me know anytime you may need to use the scanner.
:)

 

Bill, I might just have to take you up on that scanner deal. Just e-mail me your phone number or something and we'll see about getting together. Sometime this weekend would be lovely if at all possible.

 

You have about covered most things. Just a thought, could your O2 sensors have been contaminated from all the work you have been doing and there by coated? (Vapors from certain sealents will do that among other things.) If so, they will not send the correct reference voltage to the ECM. If it got bad enough it might set a code, but not always.


[Modified by ittlfly, 9:53 AM 7/20/2002]

 

nathan, it doesn't sound like you have a vacuum leak. 13" of vacuum is about correct for a HOT cam. (i bet your friend's car doesn't have a leak, either.) plus, if it were a leak, but so small that your idle vacuum were still that high, you would just barely see the consequences at idle only. and it would be a small enough leak that the stock ecu could correct via O2 sensor feedback.

your "diagnostic" sensor is highly suspect, at this point. this is basically proven by how the engine's behavior with the larger injectors mimicked an overly rich condition, yet your sensor said otherwise.

do you have software to data log from the ecu? or even a way to read the stock O2 sensor voltages?

are the elements on the MAF sparkling clean? (do you use an oil type air filter?)

all cylinders are hitting properly?

lastly, the plugs out of my car came out deathly white. it smokes rich on the dyno at WOT, and seems to cruise properly (O2s switching), yet still ultra clean, white plugs. so i wouldn't worry too much about that.

 

I think I'm going to go buy some new O2 sensors. The over sized injectors have got me curious about them.

I talked to our local mechanic, the guy who diagnosed our blazer, he is going to take a look at it for me tomorrow if I don't have it fixed by then. He has scanners and such and should be able to diagnose it pretty well.

He did however mention most of the things that I've already covered.

 

Ok I replaced the O2 sensors with a non Bosch brand :). It seems to be running a little better now, if nothing else my A/F gauge is acting a little more normal.

It still acts up a little when I first fire it up, but not as bad. It also seems to have a small stumble when I punch the gas. I've got new plugs on the way, I'll replace them tomorrow just in case the old ones are ruined by running lean for so long. I don't know if that's possible, but changing plugs with the headers is fairly easy.

 

Hey nathan,
I just got back online now and read the posts.Since youre doing some work and possibly have that mechanic help you,I'll wait to see what else you can find out.If after some work is done and you still need to use a scanner etc,let me know then.
Hopefully its all going to be good after the plug changes.
Keep us posted or email me if they cant find anything out for you.
:)

 

Nathan,
How ya coming along? with all the obvious checked, I would wager on the high side that you problem is sensor related, i would get the old books out and start systematically checking for correct sensor reading voltages on all of them. i have seen lean conditions happen when a sensor is still working enough to keep you SES light out, but not truly working to get your car where i needs to be. being a 92, try the MAP Sensor, your cooling sensors, your knock sensors, O2 sensors, IAT, TPS, etc etc.. check them all, then i would return your hunt to the mechanical side. feel free to shoot me an email or give me a ring, perhaps there somehting overlooked. Best of luck and feel free to contact me, info is below!


Best Regards,
Chris Polanski
Next Generation MotorSports
910-232-2451
Fax 910-452-3516

 

I ran around for a year runnig rich (black plugs & exhaust) All the while getting code 44 lean mix,because I thought my new NAPA O2 sensor was ok.Then I got one from Chevy & cured the problem.So I will never buy any sensors from anyone other than Chevy. :chevy

 

Alright, so I just got back from my diag guy's house. We hooked it up and drove around the block for a little while, etc. I have got to get one of those Snap-On scanners!

Anyway, it indicates that my O2 sensors are switching properly and if anything the car is running a little rich. Goes to tell you how accurate the A/F gauge is huh?

Anyway, we started looking at the IAC and found that unplugging it doesn't affect how the car runs at all. We bypassed the pressure switch on my A/C (it's currently empty) and turned on the A/C. The scanner read the requested increase in the IAC position, but the idle didn't increase at all. This leads us to believe that the valve is most likely stuck.

Also while we were talking we watched a plug boot start arcing across to the header in broad daylight! That explains the misfire I very recently picked up.

So, the car is actually running a little rich despite what my gauge says, the small misfire is pretty obvious at this point. That leaves idle as the only problem the car has, perhaps the IAC will fix that. I'll have the new one in tomorrow.

 

A good scanner is a must have when doing your own work..glad to see you picked something up off the scanner and hopefully it will be the fix.

Do you remember what your IAC counts were when using the scanner?Just wondering.
Usually if the number is 5 or less at idle and creeps to 0 counts,its a misadjusted min. air speed screw or false air leaking in somewhere.When I turn the key to ON,the IAC counts usually go straight to 144 before starting.If it stays too high or too low and doesnt move,its usually defective.
Those scanners are your eyes for inside where you cant see.

Anyways,you can sometimes a used snap on scanner from the snap on dealers.I got mine used several years ago for a good deal.
BUT,I will need the new cartridges if I want to be abe to hook up cars made after 1994.Mine cant go that high.I hear the new cartridges are big bucks.Keep that in mindIF you buy used.New,they run like 2000 bucks or something!!!

Good luck and keep us posted.
:)

 

The IAC counts were above 100 all the time. When the A/C was turned on it went up several but it didn't actually change the idle. Since it stayed at 100 engine running or no, that's what makes us think it's stuck or something.

I just took the old one out, there wasn't anything obstructing it, but since I've already paid for the new one I'll just install it tomorrow when it gets here.