Ben Taylor

I have installed headers, a new intake manifold, and put a new camshaft in my 81. Now it's running lean. What do I need to do to fix this? I have the stock computer controled Quadrajet, where can I get the parts for this?

Riceater

Did you reattach the O2 sensor?

As far as i know, there is no adjusting an 81 q-jet.

Ben Taylor

I put the O2 sensor on the reducer.

Fast81

There is a Hypertech replacement chip for 81-82's.
Part # 303012/303013
Check out http://www.corvettecentral.com
I think it even states in the product write up that the chip is for just the mods you describe.




[Modified by Fast81, 9:04 PM 9/10/2003]

Rich's78$pit

Only the primary side is controlled, the secondaries are not. So you need the chip for the primaries and a conventional rod change on the secondaries.

stickboy

Did you use the stock sensor, or did you put in a heated 02 sensor? I think you may need a heated one. Also you will proabably need to adjust the carb. Get the shop manual or the book by Doug Roe. these will tell you how to adjust it. The only thing a new chip would really do it adjust the timing. Try advancing the timing some, this will help if you need more advance. I'm still running the stock chip in mine. Next mod will be headers and dual exhaust, I plan on installing a heated o2 sensor with it.

UKPaul

How do you know that it's running lean? Error code, pinging, gut feel? Last winter I fitted Dynomax ceramic coated Headers & put the stock O2 sensor in the reducer. At the same time I was doing some work on the carb & set the lean & rich stops according to the manual (& Doug Roe's book is really useful). I've got a CompuCam fitted, performer manifold & 2 1/2" duals with very unrestrictive mufflers, so was expecting it to run lean & give O2 sensor warm up problems. It runs just fine! The sensor seems to warm up OK (no odd error codes, but I do always let it idle for a min or so from cold b4 driving). Summit told me, when I ordered the Headers, that a heated O2 sensor wouldn't be needed.
I don't get any Check Engine warnings so figure that it can't be running lean on the primaries. Now the secondaries are a different story! I feel that they are running slightly lean, but just try getting alternate rods/hangers in the UK :(
I've got a Hypertech chip fitted (stage II) which did improve low end power (which had dropped off after fitting the cam). The chip may alter the fuel map (how do you find out??) & I'm convinced that it's altered the advance curve. I wouldn't have thought that it would be required to get the mixture correct after fitting Headers. The computer should try to get the optimum mixture normally, so even if the chip does bias towards a richer mixture, the stock chip should keep the mixture at the factory set ratio (assuming the carb is set up correctly).
I also set initial advance to 11*BTDC (stock = 6*) which made the motor "pick up" better (it's worth doing this anyway).
The computer works by reading the O2 levels & adjusts the primary metering accordingly. If it's running lean on the primaries the computer should supply more fuel to compensate. If it can't then it will flash up a Check Engine error. Correction: it will, I set mine too lean once & got non stop flashing from the light. If it's running lean on the secondaries then I'm fairly sure that the computer won't tell you as it'll probably be running in open loop (it runs open loop at WOT, allowing the carb to behave like a normal Q-jet, ie the primaries are set at full rich condition & the secondaries just do their thing as normal. The O2 sensor is probably being ignored in this situation).
If you could post up why you think it's lean somebody here may have an answer. With any luck Dallanex will post a solution. He's also been through E4ME setup thoroughly, but is blessed with a better memory than me :D
:cheers:
edit: check for air leaks at the carb base.


[Modified by UKPaul, 7:01 AM 9/11/2003]

Gator81

Hey, Paul, how's it going? :seeya
Pretty complete response to Ben. :thumbs:




[Modified by Gator81, 7:39 AM 9/11/2003]

UKPaul

Hey Gator! Good to see you back on the ether :) Email will be on it's way shortly :thumbs: A simple answer to the question would be "Downhill"!! ;)
He caught me in one of my more lucid moments :lol: But I'm sure I've forgotten an important/crucial thing. You know how it is..... if you don't touch the carb for a few months then you tend to forget some of the fine details, which are usually the important things. The next time you adjust it & the car is coughing & spluttering you'll suddenly think "Oh yeeeeeessssss, that's what I did wrong last time. D'oh" & you'll remember it again. And by typing this I've just remembered what it was! :D

Ben, CHECK FOR VACUUM LEAKS!!!! I had lean problems for months after getting my Vette, which turned out to be a vacuum leak in the remnants of the EGR system. If you're getting a computer error telling you that it's lean then go through the vacuum system thoroughly. I wasted days & days (and a lot of posts!) over several months trying to find that problem, but in my defence I must say that Bubba was particularly cunning that time :)
:cheers:

Ben Taylor

The car overheats now when I go up hills, and when I'm idling in traffic. I know it's not the cooling system. The spark plugs are all white and kind of glazed. The check engine light doesn't come on, and the engine doesn't seem to have any problems. I couldn't find any vacuum leaks anywhere.

This started right after I installed the headers.

Rich's78$pit

Can anyone answer UKPaul's question (for sure) if the computer will definitely set a fault code if you are too lean? It doesn't seem to be happening. I think the stock jets are not big enough (suggest you go up 2 or 3 sizes) and even though the solenoid that raises the needles in the jets lets them go up in response to a lean signal from the O2 sensor, there is not enough metering area (fuel flow) with the stock jets. Why not just increase the jet size and see?

UKPaul

I checked my manuals last night &, if the computer & the rest of the system is all OK, an error will be displayed if the primaries are running too weak.

Ben, I'm guessing that you're determining that it's overheating by the temp gauge reading???? What Headers have you fitted? Do they run close to one of the temp sensors? It could be that the Headers are radiating enough heat to cook the sensor, giving a false reading? What I do know is the 1st thing my ceramic coated Headers did was to fry my starter motor :(
Is the auxiliary fan cutting in OK?
Idling will cause a lot of heat build up under the hood, especially with Headers fitted, as there's very litle air flow. Driving up hill with the engine under load also causes a lot of heat.
This may sound a little far fetched, but are the Headers/pipes running very close to the cooler lines from the transmission? I fitted my Headers at the same time that I fitted a 200-4r trans & both the coolant & trans fluid were running too hot, but only at slow speed around town & after long periods of idling (I never tried any hill climbing!). A blast down the highway cooled both down to normal temps. I'd put this down to the new tranny & higher stall converter, but it could've been due to the heat radiated from the Headers cooking the trans fluid (in both the cooling lines & pan). The hot fluid was then pumped into the rad where the extra heat was enough to prevent the coolant from cooling enough. I fitted a tranny cooler in the line before the fluid reaches the rad & the trans fluid temp is now a bit on the low side (I should have fitted a smaller cooler) but, surprisingly, the engine coolant sits rock steady where it should do. Even trying my hardest to get the temps up on the hottest day on record here (100F) I couldn't get it to go above 190F (180F stat fitted). Coolant temps of above 220F were easy to get b4 fitting the tranny cooler.
As I said, I thought it was due to the new trans, but it could very well be down to the Headers. It sounds a bit far fetched, but I once managed to literally get the fuel boiling in the carbs on an air cooled engine. The carbs were mounted (thermally isolated) about 3" away from the head & it happened after a period of mountain climbing followed by idling in heavy traffic. The only way the carbs could be heated was through heat radiation. I pulled the plugs & they were very white & glazed. I then used lower gears in the mountains (less engine load = less heat) so that the engine ran cooler, didn't sit idling in heavy traffic & the plugs went back to their normal color. So I'm pretty sure that plugs that show signs of a weak mixture might just be showing that the engine is running too hot (assuming that the timing isn't to advanced).
If the heating problem wasn't caused by the new cam & intake & only appeared after fitting Headers then I'd try wrapping the Headers to see if it solves the problem.
Also check that there isn't an exhaust leak between the Headers & Head as a leak here can cause severe overheating (you'd probably hear it if it was leaking).
Good luck,
Paul

Dalannex

Hello all. I'm back again for now, then gone for a few days. I need more time off at work. :lol: Anyway, sounds like you have a lot of good advice above. Check it all. It also sounds like you have good knowledge of what you're doing from your diagnosis of the spark plugs. Are you familiar with the rich and lean stop adjustment screws on the E4ME? The rich stop is the one that could help you out a little bit, however I would think that if you set it up according to Doug Roe's book you would be good. You will find it real easy to do this if you buy a lean and rich stop setup tool kit from you auto parts store. Or if you take the top off of the carb you will see a screw sticking down on the bottom of the top with a large flat head. This is the rich stop screw. Screw it into the top a turn or two, or up when the top is installed and you will get a little bit richer running while still being in your dwell range on the M/C selenoid. It would be helpful to make up a little harness to fit between the O2 sensor plug in that allows you to hook a multimeter up to the O2 sensor while it is connected and working. One wire is the signal wire, one is ground, so if you fab up 2 connectors that will hook up to the O2 sensor plugs (I robbed a couple of plugs off of a junk car) then just solder in 2wires long enough to reach the driver seat, plug in between the sensor and the harness that goes to the sensor, hook the + lead of a digital multimeter to the signal wire, hook the - lead to the ground wire, then read mV while the car us running. Once it's warm it should read between 100 and 900 mV. 100 is lean, 900 is rich, 450 is about 14.7/1 air/fuel. Also hook a dwell meter up to the M/C test connector with the dwell meter set on the 6 cylinder scale and see what that reads. That will tell us to a point what the ECM is trying to do. I also hook up another homemade wiring harness to the TPS to see what it is doing with my multimeter, but that's another wiring harness to build. If you don't want to do all of that (I would though) screwing the rich stop screw up a turn or two would richen it, but whether or not it's too much would be tough to guess without at least doing the dwell meter thing. If you turn the rich or lean stop screw remember about how many turns you go so that you can go back if need be. If you forget it's not the end of the world though, we can still get it back alright, it just takes a little bit more.


-Justin

clem zahrobsky

both the "rich stop" and the "lean stop" on the primary side is adjustable on GM computer controlled Q jets. this contols how much the metering rods move and where they are located in the primary jets. the secondary side can be richened using different rods. secondary rods can be gotten from edelbrock thru speed shops


[Modified by clem zahrobsky, 11:04 AM 9/12/2003]

UKPaul

Hi Justin,
Just turned on signatures & I've got to say... looking good :thumbs:
With this overheating problem I've purposely kept away from carb adjustments for 2 reasons:
1) I'm assuming it's set up correctly as it used to run OK
2) Problems only started after fitting Headers.
As it's so easy to mask problems with a mixture change (incorrect timing, wrong grade of plugs, etc) I always adjust the mixture once everything else is spot on (& it does sound like the Headers could be cooking the engine bay).

But you've given me an idea which would also help Ben out (maybe). Remind me (it's been a while since I've touched the carb), the solenoid plunger is adjusted 10 times/sec, by applying a variable voltage, & the rich/lean limits prevent it from going off the "ends" of the adjustment range. The solenoid plunger should be at rest in the fully rich (up) position (giving a limp home mode that won't hole a piston if the ECU dies) & the ECU supplies a voltage which pulls the plunger down to lean the mixture out when it needs to. Full voltage will cause the plunger to hit the lean stop, giving the leanest mixture possible (which is determined by the position of the lean stop - combined with any vacuum leaks ;) ).
Here's the idea: How much extra range has the ECU/plunger got ie. is the lean stop reached at almost full voltage, or somewhere before, leaving a little something in reserve???? If the rich stop is raised considerably, would the plunger still be able to be pulled down to the lean stop? Obviously, moving the rich stop too far up would cause problems, but I'm wondering how much "slack" there is to play with. If the lean stop is left in the original postion & the rich stop is moved up, but there's still enough range in movement for the ECU to drive the plunger between the 2 stops, then I could be onto something (I'm figuring that the ECU is fairly dumb with a decision process along the lines of "Rich mixture, up the voltage, still rich, up the voltage," then "mixture OK, hold the voltage" or "rich mixture, at highest voltage, flag rich error condition"). If the rich stop is too high, but there's enough control on the plunger to be able to pull it down to the lean stop, then the ECU should just position the plunger at the correct position. As far as I can remember, the primaries are run in the full rich position on cold start & at WOT when the system goes into open loop. So if the rich stop was set artificially rich then the extra rich mixture would slightly alleviate my suspected weak secondaries mixture (not a lot, but it all helps!).
I've tried to find alternate rods/hangers here & just get blank looks or told to fit a Holley :rolleyes: so I'm starting to take those crazed Friday afternoon ideas more seriously :D
I guess the easiest thing to do is to adjust my rich stop & see what happens but as I've just typed all this, whatdya reckon????
:cheers:
p.s. take a break from work :)

edit: I'm sure there's a basic flaw in plan A above!

Ben,
I should have realised this straight away. Are your Headers ceramic coated??? Summit told me that I wouldn't need a heated O2 sensor with my Dynomax Ceramics, but if you're Headers are losing a lot of heat it could be that your O2 sensor isn't getting up to temperature, causing all sorts of erroneous readings & throwing the computer control of the carb out. When I was looking at getting Headers I read somewhere that problems of this sort usually happened at idle & were cured by either a heated sensor or by wrapping the Headers.


[Modified by UKPaul, 11:11 AM 9/12/2003]

Ben Taylor

I have the Dynomax ceramic coated headers. I'm also running plugs with the stock heat range. I've tried running with my timing to spec, a couple degrees advanced, and a couple degrees retarded, and it doesn't seem to make any difference.

Dalannex

Paul and Ben, I believe the MC selenoid changes by changing on time and off time at a always constant voltage because when we check the MC selenoid with a dwell meter we are actually checking selenoid on and off time. To lean the system out the ECM sends voltage to the selenoid and holds it for X amount of time. This is a very short time since it does this 10 times a second. If it wants to run richer it spends less time with that voltage supplied to the selenoid each of those 10 times/second. Now, what I am wondering, (with Ben especially) is if the new mods don't require a little bit richer mixture, but the carb was set up a little bit towards the lean side before, so now it is still pulling the selenoid down 10 times/ second, and releasing it immediately because it wants more fuel, which lets the primaries spring up until they hit the rich stop, but it is still not enough fuel. If the rich stop was moved up when the selenoid was deenergized the primaries would go up, letting more fuel in than now, which would result in a richer mixture, and my even get back into a range that would require the ECM to hold the primaries down longer to get back into the 14:7/1 air fuel ratio. Now this does of course require that everything is working correctly, especially the O2 sensor (I am in the middle of a test between heated and non now to see if there is a difference now), coolant temp sensor, and TPS. By sticking a piece of wire or small tube in the D shaped vent hole on the top of the air horn you can push down on the primaries to get a measurement of how much travel you have in your primary setup currently. This won't tell you without dwell meter reading whether or not you are exactly in the range you need to maintain the proper air/fuel ratio, but it would give and idea of how much travel you have. There should be 1/16"-1/8" of travel. There are also plugs on the air horn to access the rich and lean stops without tearing the carb apart.

Paul, I'm going to be shooting you an email.


-Justin

clem zahrobsky

1981 corvette carb # 17081217, float 11/32",lean setting 1.304 use gauge,rich setting 4/32" travel,idle mixture screws 3 3/4 turns out,air bleed 1.756 use gauge,final setting done on car. you could increase the 4/32" to 5/32" and see what happens. you could also set the lean stop at 1.336 and leave the rich setting at 4/32" travel. with the proper tools if you set up the plugs in the carb top so you can remove and install the easiley you could try the differt adjustments without removing the carb top. the delco carb book does not give the primary jet or rod size for the computer controlled carbs because they sell the jets and rods as a pair only,so you would have to measure them if you need to go richer :chevy

Ben Taylor

I just checked the amout of travel and it's 5/64". I'm going to look into adjusting the stops when I get home in a couple hours.

Dalannex

Judging by that I would say that your rich stop needs to come up. It would probably be a good idea to get a set of setup gauges and use them to set it up.


-Justin