I've got a 85 z28 lg69 305, with the stock 4bbl q-jet(q-junk) carb. I'm getting ready to swap it out for a Holley 4160-1850(I got it for $20, I just have to rebuild it). The Holley is a 650 cfm with vaccum secondaries, and manual choke. I have a couple questions:
1. Will the Holley bolt right on to my q-jet intake, or will I need an adapter?
2. Will switching to a non-computer-controlled carb mess up or effect my ignition and distributor?
3. Does this sound like a good swap to gain a little power?

 

personally i don't think it's worth it at all. you won't gain anything by switching to a holley carb other than a hole in your wallet. Not to mention you'll need a vacuum advance distributor and all the other things going non-cc. If you want power out of your 305 the factory carb is ok to use....despite what other people say. You haven't swapped cams, intake, or heads yet in search of real power anyways.

 

Now that's starting off on the right foot...

No, you'll need an adapter or an aftermarket intake.

Yes. As stated above, you need a non-CC distributor; and if automatic, a way to lock up the torque converter clutch.

No. As stated above, it's a horrible way to try to get power. The L69 needs exhaust, then cam (the stock one isn't bad, but there are better aftermarket out there now), then head porting. Then perhaps an aftermarket intake manifold like Action +. You will not gain any power at all going to a Holley, although if this is a dedicated racer, you might consider a double-pumper Holley. The VS won't help a bit.

 

as long as we are on this topic... I had the same question only I have the 350 with the same computer controlled 4 bbl q-jet. Is it worth my time to switch to a holley (BTW: I have an automatic).

Either way I may need a new carb; there's all this gasoline in the air filter.

 

i'm with you guys, i have a 84 and my q-jet is busted and **** and the connectors are bad on it, i dont really wanna keep it. i would rather go with like a holley or edelbrock carb and and get a new intake and if i have to a distributor, and then how do i love my convertor up? if its easyer to keep the computer controlled stuff where can i get a new cc q-jet. and a new intake that will give me more power?

 

By the way, the reason I'm switching over to the Holley is because right after I bought the car, I noticed that the air-flow sensor, and another sensor(I forget what it is called) were disconnected, I tried to connect them back, but the were nutted/capped off. I asked my mechanic, and he said that the previous owner probably had a problem with either the computer or the sensors, and just disabled them. I don't claim to be a car genius, but cutting off your sensors just doesn't seem like a good idea. It would cost over $700 for the new sensors and stuff, so I decided to just get rid of the cc carb and put a Holley on. Does anyone have any idea why someone would chop off the sensors?

 

yeah most likly there was something wrong so he capped them off. dude i feel ya i have lots of hoses and **** capped off for no reason, i just want to go old school with a nice old carb setup. but how do we lock up the convertor?????

 

OK... Here's some food for thought, Especially for those of you who think that you need to ditch your CC HEI when you swap to a Holley from cc Carter...

I have an '86 TransAm LG4 305 which used to run the CC Quadrjet. I am now using a 4160 Holley with NO emmisions equipment fitted. It's all been stripped out and I'm running the original (Apart from an Accel cap) H.E.I distibutor from the original ECM, and NO, it does not run in 'Limp' mode. How is this possible?

If you remove your O2 sensor wire, with this model of ECM, the internal circuitry (Just a precision resistor devider network really) of the ECM produces exactly 0.45v on the input pin from the sensor! I can prove this with the diagram from the factory service manual. Also I have physically measured it at the pin itself with a DVM.

What this means is, the ECM still thinks it's got the O2 mixture correct and, when the temperature reaches the Closed loop point all timing is then controlled by the ECM as normal! You may now tune your Holley however you want.

Combined with an Edelbrock Performer manifold, no Cat', and a performance muffler this makes my non internally modified 305 go like hell! The original HEI timing is still controlled by the ECM in combination with the knock sensor, Temp, Vacuum and Barometric pressure sensors to produce an excellant result.

Now, unless the '85 ECM is different than the '86, then you really dont need to do that much to change over to the 4160 Holley.

Just thought you should know this... Thanks for putting up with a rather long winded blurb but It may be worth it... Kind regards...
Geoff

 

hum i might try this out with a 600cfm holley i have sitting here.

 

It isn't. You probably don't understand limp-home mode.

There is some advance built into the module based on RPMs. However, without the TPS input, the ECM will not get involved. The advance you do get may be adequate for WOT use by setting total timing, but you will not get cruise advance, for example, that is needed for decent mileage. You may also have start kick-back problems, depending upon how much base timing you need to put into it in order to get the total WOT advance needed.

 

Sorry, mate, but your'e wrong....
I'm at work at present but will double check this when I get home. From what I remember the ECM receives a 'Referance' Pulse from the HEI unit which directly relates to the RPM of the Engine. This is how it knows what part of the timing lookup table to access and provides the correct timing right across the RPM range. I have checked this, also, using a timing light. The need to muck around with mechanical distributors is not needed....

By the way... I made an error when I stated I used to run a Carter, sorry... Meant Rochester (Got Carter on the brain at present).

Thanks... Regards... Geoff.

 

Well, I guess I'll have to do some more experimenting. I checked timing with the 4-wire disconnected, and it will advance a little with increased RPMs, but nothing like when the 4-wire is connected. I didn't try it with the TPS & O2 disconnected, however.

 

I have double checked the service information and confirmed that the TPS is used ONLY for mixture control. I will post a link to some JPG's I've scanned from the service manual, or maybe put together a Technical article on the subject?

All inputs required to run the HEI, or EST (Electronic Spark Timing) are...
RPM - Provided by the HEI unit Ref signal.
Load - Provided by the MAP (Vacuum).
Temp - Obvious.
Barometric pressure - Sensor under dash in my case.
The timing is further influenced by the knock sensor circuit known as the ESC (Electronic Spark control). This is basically a microphone in the block that passes its output to a black box which filters out everything but the 'pinking' noises and informs the ECM if a knock is detected. The ECM then simply retards the timing a little..
Not to sure what you mean by the 4 wire? If you are refering to the 4 wire connector from the HEI unit, then you are isolating the HEI unit from the ECM and little or no timing advance should be expected.
just a quick additional point.... The ECM takes over the timing for the HEI at RPM's at or above 400RPM. One of the 4 wires to the HEI is pulled high (5V) by the ECM to tell the HEI unit that it will now supply the timiing signal for the ignition.
Hope this clears some points up on this, As I said I may put together a tech article if you guys think it will help?
What scares me is that there may be be large pile of needlessly discarded HEI units out there. Use them... These are a good, VERY reliable piece, I have not had to touch mine since I set the base timing aprox' 4 years ago!
Thanks and Kind regards...
Geoff

 

So does this mean that I can throw a Holley on by only disconnecting the O2 sensor? Or is there something more?

 

Basically... Yes. Take the old carby and it's electrical connections away and disconnect the O2 sensor. So long as you dont effect the circuits and sensors related to the HEI timing (EST) or the Knock sensing (ESC) system you should be fine.
The system I have working is very tidy, no EGR or the preliferation of hoses etc. Ensure you do not introduce any vacuum leaks also. Cheers... Geoff

 

I'll be waiting with baited breathe to hear how it works.

 

So if this doesn't work, what's the other way to do it?

 

If it doesn't work... You may have a different ECM, in which case, I'm buggered if I know because it DOES work on mine! Just have a go... What could possibly go wrong???? Regards... Geoff

 

I know they did some strange things with the vehicles they shipped to Canada, who knows what they did when they went RHD...

 

Sorry, but I'm not buying the magic this time. Even if you were able to "trick" the O2 into producing sane readings that isn't the problem. The mere fact of unplugging the mixture control solenoid and TPS in the carb from the ECM is the problem. That fact alone will throw the ECM into limp-home mode, accompanied with a very WEAK advance curve compared to normal. Not NO advance, WEAK advance- as in not much.

Bypassing the O2 is not at issue here (and I doubt it's working quite the way you think it is, but I'm not going to open that can of worms).

Anybody feel like trying me out? OK, go unplug the big blue 2-wire connector from the top of your computer controlled QJet and start it up. If you didn't have the check engine light on constantly before, you do now (assuming the bulb isn't burned out). Go drive it around a little. Does it feel responsive? What about WOT power? Doesn't really make much power does it?

Think maybe that bypassing the O2 as described will now fix this? OK, go unplug that, too. Try it for yourself.

 

You wouldn't get any mixture control that way. But, would you get timing advance? If you do, then a mechanical carb would take care of the mixture control.

I have a 1903 Edelbrock and a 3310 Holley sitting in the garage attic. Perhaps some day when there aren't any honey-do's in the jar, I'll put one of them on and see what happens.

 

This is the last time I'm replying to this thread...

1: My '86 TransAm is a USA model that was imported to Australia where it was converted to right-hand drive. I bought the car after it was imported to New Zealand. This is a standard USA model vehicle in ALL other repsects.
VIN is 1G2FW87H3GL240465
ECM is 1227169

2: Unplugging your existing Quadrajet and expexting to run is like 'Pissing into the wind' ! Of coarse it wont run properly. Replace it with a mechanical carby, like a Holley 4160' , disconnect your O2 sensor and it will work. Put a timing light on it and see for yourself.

GM, or AC Delco, or whoever designed this system did a great job. You can disable one part, the mixture control, and the other part, the HEI EST, will still function. And I dont mean in limp mode. By the way, My vehicle is a T5 manual so I know nothing with regards to how the ECM relates to Auto's.

I no longer have my space on Tripod to post the JPG's I scanned from the Factory Service Manual but will put together a tech article on this in the near future.

I have done it... It works... I have proved it works... My car is a daily driver and has been for 5 years. I have used a timing light to prove the advance is good and double checked with the manual circuits and trouble-shooting procedures. What more can I do?

Thanks for the interest and watch the tech' articles... Great site, by the way guys... Kind regards...
Geoff

 

Getting ANY timing advance is one thing. Getting enough and getting it fast enough is quite a different question. Limp home mode doesn't mean that it stops supplying timing advance to the distributor. It just gives it a very weak advance curve. Could you bump up the initial timing to compensate to a certain degree? Sure. Is it a rig job? You bet.

Once the ECM sees that the computer controlled Qjet is gone (by virtue of the M/C solenoid and TPS being unplugged) it's gonna throw the penalty flag.

Like you, I have also played around with these things a bit.

The O2 sensor thing is a red herring. That's not the problem. having the ECM not see the M/C solenoid and TPS is the problem.

 

I thought I would respond to this post because I'm the one that started this whole discussion. I finished installing my Holley 4160, and it works great! All I had to do was disconnect the conntectors to my old carb, and put on the new carb and the adapter. I just left the connecters sitting there. My torque converter, ECM, and ignition all work fine. I didn't have to make any modifications at all. The only thing that happens is my check engine light is always on, but that's no big deal.

 

A few observations, if I may:

Problem 1: The ECM treats a constant 450mV as a sign the O2 isn't warm yet. As a result, the ECM will PERMANENTLY stay in "open loop" mode. I suspect this is what you're seeing. In "open loop", the ECM does have a default timing map that is much better than the limp home mode. I've certainly never had driveability problems when the car was in open loop (they always started in closed loop). Again, if this was an auto car, the TC would NOT lock--it only locks in closed loop. As it is, I'm sure the map is more conservative than the closed loop map precisely because the engine doesn't really know what's going on. The ECM also would operate on some pre-defined MC dwell, but that's irrelevant since you don't have an MC solenoid. Lastly--and here's the kicker--almost NO codes are thrown in open loop mode. I suspect this is why you don't get a CE light. The only one I've EVER seen has been "code 12"--which you won't get because the CC HEI unit is still present. Certain emissions equipment also does not function in open loop--the AIR diverter sends air to the ports instead of the Cat (not sure if the divert function still works in OL, I suspect it does). Not sure what EGR would do, it seems to vary from ECM to ECM. On an LG4, canister purge and EFE are completely vacuum controlled, so those would work fine.

Solution 1: If you were able to get at the hex code in the ECM PROM, and modify the "open loop" timing map, this method would probably work great. I can't, at this point in time, see any other flaws with this setup on a STICK SHIFT car, assuming offending emissions equipment (AIR and EGR) are disabled/removed or altered so that they function properly in open loop.

Problem 2: If you have the MC solenoid disconnected, the computer definitely operates in some sort of degraded mode in closed loop. I've never been able to figure out exactly what it's doing, but it DOES seem to give a weaker spark advance curve. I suspect it also might not lock the converter or do any number of other things. What I don't know is if the absence of the MC solenoid affects anything in Open Loop.

Solution 2A: Fool the ECM about the MC Solenoid. This should be simple enough. Unless the ECM is advanced enough to be able to tell the difference between it and a resistive load (which I highly doubt), you should be able to fool it by putting the correct amount of resistance across the connector, using a suitably high enough wattage power resistor to handle the load. Since you're operating in open loop, the ECM will not throw exhaust rich/lean codes, or bitch and whine about the dwell being pegged high or low. The dwell probably follows a preprogrammed map in the ECM, but it doesn't matter, since it's not actually DOING anything.

Solution 2B: Modify your setup to operate in Closed Loop mode. This one almost isn't worth thinking about. Even if you could get past the "450mv means cold O2" coded into the system, unless the O2 voltage is EXACTLY 450mV, the ECM is going to try and ajust the mixture by varying the dwell. And since you've completely removed the ability of that to AFFECT anything, pretty soon you'll be staring at another check engine light. What happens is that ECM will KEEP adjusting the dwell the same direction, in effect saying "Dammit... too rich... Dammit, that wasn't enough, still too rich... dammit, what is this moron doing, dumping raw fuel down the primaries? Aw hell, I give up... eat check engine light you cro-magnon!"

Notice you've now traded your headache for an upset stomach. No, the CE light doesn't cause the same code. If you REMOVE the light, it's entirely possible the timing curve might still be correct (rich exhaust, in particular, does NOT seem to trigger in limp mode. The performance is about the same). Just to be safe, bias the O2 voltage to like 600mV--the ECM *might* retard timing if it senses a constant LEAN condition. But, it do NOT think it is possible to "simply" fool the ECM into running in closed loop AND prevent it from throwing a CE light for rich or lean. You'd have to design some sort of feedback circuit that fed the right response back to the ECM based on what it was sending to the MC solenoid--otherwise sooner or later you're gonna get the happy yellow light.

Unfortunately, if you removed the light to deal with the above problem, you now have no light to see if there are any OTHER problems. Keep in mind the ECM is capable of throwing a TPS code and will do so in closed loop under a few circumstances. It has a bitch of a time telling when there are bad spots on the TPS, or if it's not reading RIGHT, but it is capable of determining that it isn't reading at all. So now you have to put two resistors across the TPS connector so the ECM doesn't think it's disconnected. Guess what happens next? Assuming the TPS doesn't screw your timing map up (and you say it does not--I suspect you are right, it seems to use the VAC sensor more for timing), you're still hoping the ECM won't notice that the TPS is a constant, never changing voltage. I'm not sure I'd bet on that one. The ECM logic is bad, but I don't think it's THAT bad.

Conclusion: If you can hack the chip, find the Open Loop timing table, and modify it, this might be a damn neat way to do timing. Otherwise, I gotta put this in the "nice try, but no cigar" category.

 

Uh, not possible. The ECM uses the TPS information to determine whether or not to lock the torque converter. Are you sure the converter is locking?

Also, I'm surprised about the check engine, honestly. Why don't you pull the code and see what it is? It might be interesting...

 

How do I tell if the converter does not lock up?

 

A couple of different ways:

1) When cruising, give it a little more gas, but not enough to make it shift down. If the RPMs jump up a little immediately, the TC isn't locked. If the RPMs increase only as vehicle speed increases, the TC is locked.

2) At a cruise, under slight power (either up a small incline or accelerating slightly), keep the accelerator constant and depress the brake pedal slowly. If the TC is locked, it will unlock as the brake pedal is depressed and the RPMs will jump up slightly. If the TC wasn't locked, RPMs won't change.

 

interesting topic. I'd love to see the outcome of this. My friend has a '85 LG4 with the stock Q-Jet and switching to a holley would be cool if he didn't have to worry about all the connections and changing from HEI. TC lockup isn't an issue since I am rig a switch to do that to save him some gas mileage. I wanna see that tech article whenever it gets posted too.

 

1. What would be the the drawbacks if my TC does not lock?
2. Is it possible to lock it w/o having a q-jet?

 

1) Reduced gas mileage and excessive heat generation. There have been reports of 3-4 clutch pack burn-out when the TC doesn't lock like it's supposed to.

2) Yes, check the tech articles. You can also get a retrofit kit from Summit/Jegs.

 

You can also rig up a switch coming from you diagnostic port under the steering wheel to automatically lock up the TC. Check the tech articles, it's amazingly simple.

 

If it helps any last year I had my TPS hang up on me. The plunger wore through the side and was binding. I disconnected the TPS to keep the car running decently enough to get to the parts store.

Things I noticed:

1. Lack of power throughout the entire RPM band. Including WOT which is primarily metered by the secondaries. I attributed that to lack of timing advance.

2. Check engine light

3. No torque converter lockup.

4. The car ran (best guesstimation from the stock gauge) about 20* warmer.

5. 1/4 tank of gas in 25 miles of driving

 

You weren't in open loop though. The disconnected TPS makes the ECM very angry in closed loop.

 

Im running my 84 305 with a holley avenger no o2 cc hei the tc kick down cable has no where to connect and long tube hedmans. my car runs fine but about the locking of the torque converted didnt some 80's gm cars come without lockup tc's?

I have no knock sensor so is my car good with the stock distrib?
Im problay gunna get a non cc distrib anyways but dont feel like spendin the money if i can run withe the stock one.

 

ok seeing how everyones talking about tc lock up here ive got a couple questions. how can you get the tc lock up to work with no ecm or stock ecm wiring? is there a way to just get the plug for the trans and wire it up a certain way? or am i just screwed and gotta spend the $70 to buy the tc lock up kit from jegs? i know my tc lock up wasnt working when i drove my car which resulted in about 8mpg city driving and 12 mpg highway. it was doing about 55 mph at 2500-2700 rpms which it should of been about a 1000 rpms lower and it did run warmer then i liked.

 

Stock Q-Jet flows more than enough air when tuned right anyway. I won't need it, and I'd rather leave most of my emission systems in tact.

 

So, digging from way back to find this theard, but did anybody come to a solid conclusion about running CC HEI's in open loop w/ a mechanical carb? I've got a nice DUI Street/Strip that I'd hate to ditch, but my CC-Qjets got more issues than Paris Hilton, and it's got a replacement ready to go in. Should would be nice to keep the HEI, any final throughts...

 

A long while back someone reported using a CC distributor with a non-CC carb on a car that was mainly raced. By setting the max advance at high RPMs, you're basically running like a locked-out advance distributor.

Not a good idea on a street driven car.

I'm working on setting up an external TPS with a non-CC carb and CC distributor. The throttle position is what the ECM really needs to know from the carb.

 

So, the CC HEI can work with a mechanical at WOT, but only as a bandaide fix, and will not yeild good cruise mileage. Thats what I was figuring on, this thread was a ray of hope for the DUI, but that settles it, its coming out w/ the QJet, I've got a non CC HEI all ready to go.