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Thread: Ugh Carb Issues on my 81-I HATE THIS CARB! Reply to Thread
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Topic Review (Newest First)
08-27-2019 03:31 AM
The Torch Good deal
08-26-2019 09:15 PM
hamerDown Been sometime since I posted (really busy taking care of my 91 year old father) but...I did ditch the OE carb, had my old junky Qjet rebuilt and the care runs great!
I can't be more pleased that E4MC is OFF my engine!
07-13-2018 11:07 AM
immortal
Quote:
Originally Posted by hamerDown View Post
UPDATE (and a real quick response to Tom Mobley)...EGR, air pump, Cat Converter all that was removed several years ago, heat risers plugged~engine ran better with no CEL light.

I did thoroughly check for vacuum leaks...went around everything I could (headlight vacuum hoses/pods too) spraying a little 'Starting Fluid' to see 'if' Engine raised RPM's...it did not...not until the carb got a sniff.



Currently > > > Wish I could say I 'found and fixed' the problem but I did not...I removed the battery, disconnected the two large plugs and pulled the ECM out, kicked it around the garage floor, checked, cleaned the two large plugs, reinstalled it with the battery, maybe bumped some wires around and it's running like nothing ever happened however, the MCS still is not clicking at idle and I know it once did...but it's been some time.

(this Car should get better than 11 MPG around town and I baby it 140,500 pulled and rebuilt heads maybe 15 years ago, approx 3000 miles a year)

I borrowed the older Snap~On Scanner and everything from the O2 reading to Fuel Mixture and a few other readings from the Scanner were in the middle of the parameters, so it has me scratching my head...possible cracked solider joint in the ECM board? Possible funky connections at the two large ECM plugs (never touched since it was assembled in 1981)
I don't know, wish I did but, it's running just like it did prior to it running/idling bad...and especially like it seemed the ECM retarded the Timing a LOT!
Oh...and the MCS is still not 'clicking' at Idle and I know it did...because I remember it doing so, a while back.


Soooo that's my story and I'm sticking to it.
When it comes to "electronics/electrical" I'm still learning (truth is I still hate it and suck at it lol)
***All the feedback and time given doing so is greatly appreciated and I'm still reviewing all the posts


as ii answered in previous post today the e4me/e4mc is a beast, 90 percent of the computer function is to provide a smooth idle it does this by adjusting the air/fuel mixture something like 10 times a second, but once its above idle the cpu stops doing pretty much anything it does control some aspects of auto transmission function but mostly all it does is make the carb idle, and the problem is u cannot just adjust the idle higher to make it not do this because you end up with a idle of 1500 rpm or more to not have the cpu interact. the proper way to tune this is to use a combination of dwell and vacuum gauges.
start by making sure the tps sensor has the correct voltage.. then attach vacuum and adjust idle mix until the vacuum gauge is at its highest, once idle mix is set from the base screws use the dwell meter to get the proper dwell by turning the mixture screw on top of the carb until dwell is correct,, now the agonizing part of this... these adjustments must be done with the car idling at temperature... and since your issue with mostly with it not idling the start is a lot of twiddling with screws to get it to idle. (pro tip here is to ensure ur 02 sensor and map sensor are working, if one of these aint then ur pretty much sol)
07-08-2018 09:01 PM
Maniacmechanic1
Quote:
Originally Posted by hamerDown View Post
UPDATE (and a real quick response to Tom Mobley)...EGR, air pump, Cat Converter all that was removed several years ago, heat risers plugged~engine ran better with no CEL light.

I did thoroughly check for vacuum leaks...went around everything I could (headlight vacuum hoses/pods too) spraying a little 'Starting Fluid' to see 'if' Engine raised RPM's...it did not...not until the carb got a sniff.



Currently > > > Wish I could say I 'found and fixed' the problem but I did not...I removed the battery, disconnected the two large plugs and pulled the ECM out, kicked it around the garage floor, checked, cleaned the two large plugs, reinstalled it with the battery, maybe bumped some wires around and it's running like nothing ever happened however, the MCS still is not clicking at idle and I know it once did...but it's been some time.

(this Car should get better than 11 MPG around town and I baby it 140,500 pulled and rebuilt heads maybe 15 years ago, approx 3000 miles a year)

I borrowed the older Snap~On Scanner and everything from the O2 reading to Fuel Mixture and a few other readings from the Scanner were in the middle of the parameters, so it has me scratching my head...possible cracked solider joint in the ECM board? Possible funky connections at the two large ECM plugs (never touched since it was assembled in 1981)
I don't know, wish I did but, it's running just like it did prior to it running/idling bad...and especially like it seemed the ECM retarded the Timing a LOT!
Oh...and the MCS is still not 'clicking' at Idle and I know it did...because I remember it doing so, a while back.


Soooo that's my story and I'm sticking to it.
When it comes to "electronics/electrical" I'm still learning (truth is I still hate it and suck at it lol)
***All the feedback and time given doing so is greatly appreciated and I'm still reviewing all the posts
I am going with the ECM AT FAULT . BAD COLD SOLDER JOINT ON THE CIRCUIT BOARD.
YOU KICKED IT AROUND THE GARAGE AND BEAT THE SHIT OUT OF IT.
SHOWED WHO IS BOSS.

See What Gunny has to say & thinks.
07-08-2018 04:35 PM
hamerDown UPDATE (and a real quick response to Tom Mobley)...EGR, air pump, Cat Converter all that was removed several years ago, heat risers plugged~engine ran better with no CEL light.

I did thoroughly check for vacuum leaks...went around everything I could (headlight vacuum hoses/pods too) spraying a little 'Starting Fluid' to see 'if' Engine raised RPM's...it did not...not until the carb got a sniff.



Currently > > > Wish I could say I 'found and fixed' the problem but I did not...I removed the battery, disconnected the two large plugs and pulled the ECM out, kicked it around the garage floor, checked, cleaned the two large plugs, reinstalled it with the battery, maybe bumped some wires around and it's running like nothing ever happened however, the MCS still is not clicking at idle and I know it once did...but it's been some time.

(this Car should get better than 11 MPG around town and I baby it 140,500 pulled and rebuilt heads maybe 15 years ago, approx 3000 miles a year)

I borrowed the older Snap~On Scanner and everything from the O2 reading to Fuel Mixture and a few other readings from the Scanner were in the middle of the parameters, so it has me scratching my head...possible cracked solider joint in the ECM board? Possible funky connections at the two large ECM plugs (never touched since it was assembled in 1981)
I don't know, wish I did but, it's running just like it did prior to it running/idling bad...and especially like it seemed the ECM retarded the Timing a LOT!
Oh...and the MCS is still not 'clicking' at Idle and I know it did...because I remember it doing so, a while back.


Soooo that's my story and I'm sticking to it.
When it comes to "electronics/electrical" I'm still learning (truth is I still hate it and suck at it lol)
***All the feedback and time given doing so is greatly appreciated and I'm still reviewing all the posts
06-22-2018 04:51 AM
Maniacmechanic1
Quote:
Originally Posted by Tom Mobley View Post
Holley 4-bbls don't work well on Q-jet manifolds, which is what he's got. He would have to run an adapter, which are often a source of vacuum leaks.Fuel line doesn't work, need a different one. most guys and up with a rubber hose, not a step forward. various lines would have to be sorted and re-attached, including the headlight doors and A/C. Air filter won't work, hits the float adjuster front and back. vacuum line to power brake booster won't work, have to replace the distributor, it won't work without the computer. carb may hit the EGR valve. new dual feed line will hit the heater hose. have to do something with the computer and wiring harness. Fix the check engine light. Fix all the vacuum lines from the canister, re-vamp the lines as the Holley doesn't have two 3/8, actually three needed. Holley doesn't have bowl vents to plumb to the canister. power brake booster, evap and PCV. Fix the throttle linkage and TV cable. This is not a simple bolt-on change-over, I've fixed a few of these, the term that comes to mind is "butchered up mess". Did I mention the hood probably won't close with Holley on an adapter? Will it ever pass smog check again?

Have you ever done this on a nice original car? OP states he bought the car new. Think he wants it chopped up? Like I said, careful and through search for vacuum leaks hasn't even been done.
I noted early on he hates this Smog era E4MC Q-jet.
Its in his thread title.
I Hate this Q-jet.
He states he knows a Holley 4-bbl carb inside out.
He states he was a Mechanic in the past.
Knows all but Electronics.

So it makes Logical sense to give him what he really desires.

Its Not a 1970 LT1 or LS5 So he does not have a good factory Q-jet.
In Doug Roes Book ROCHESTOR Q-jet he states its not a good carb either a E4MC.

Why keep Ficking with it when it gives nothing but Frustration.

ITS JUNK.
Makes his Corvette Ultra slow.
Get passed by a Honda Tuner Kid with a Fart Can Muffler.
That kid that Blew by You does not care about SMOG.
06-21-2018 10:24 PM
Tom Mobley Holley 4-bbls don't work well on Q-jet manifolds, which is what he's got. He would have to run an adapter, which are often a source of vacuum leaks.Fuel line doesn't work, need a different one. most guys and up with a rubber hose, not a step forward. various lines would have to be sorted and re-attached, including the headlight doors and A/C. Air filter won't work, hits the float adjuster front and back. vacuum line to power brake booster won't work, have to replace the distributor, it won't work without the computer. carb may hit the EGR valve. new dual feed line will hit the heater hose. have to do something with the computer and wiring harness. Fix the check engine light. Fix all the vacuum lines from the canister, re-vamp the lines as the Holley doesn't have two 3/8, actually three needed. Holley doesn't have bowl vents to plumb to the canister. power brake booster, evap and PCV. Fix the throttle linkage and TV cable. This is not a simple bolt-on change-over, I've fixed a few of these, the term that comes to mind is "butchered up mess". Did I mention the hood probably won't close with Holley on an adapter? Will it ever pass smog check again?

Have you ever done this on a nice original car? OP states he bought the car new. Think he wants it chopped up? Like I said, careful and through search for vacuum leaks hasn't even been done.
06-21-2018 10:05 PM
goldata81 In the 14 years I've owned it and 6k miles I've since put on it, I have had no problems with the carb. It now has 91K on it. The only thing I felt was a little off with it was after starting the engine cold and it running at high idle for a bit (about 5 mins maybe), it would attempt to idle down somewhat all by itself but not to low idle. Tapping the gas would let it kick all the way down to low idle like it should when warm and it would run just fine. I am not a carburetor guy so maybe that behavior is normal/expected. Paperwork that came with the car says the carb was rebuilt but there are no details on when or what was all done to it.
06-21-2018 08:07 PM
Maniacmechanic1 I have driven 20,000 miles on the street with a Holley 770 cfm Street Avenger on my 63 Pontiac.


That E4MC Q-jet is crap next to it.


Corvette Tuned Port EFI Works Right too.
06-21-2018 07:49 PM
Tom Mobley goldata, do you have a known good computer Q-jet?
06-21-2018 07:44 PM
goldata81 Wish I was more knowledgeable on this subject and could help as I have an ’81 as well…. However, I just pulled the body off and have headed down the road of an LS swap. If you narrow down what may be the culprit and/or want to try swapping a part(s) on from a different vette that was running fine before the body pull, PM me and I may be able to help out in that respect.
06-21-2018 07:36 PM
Tom Mobley
computer Q-jet

I think you've got a vacuum leak. I wouldn't even consider changing out the carb for a Holley. You'd have to run a carb adapter since the Holleys mentioned are square bore and will not fit on your manifold. YOu'd have to change everything on top of the engine before it's over.

Have you got a dwell meter at all or borrow one? Think of it as a duty cycle meter in this case. You need to know what the duty cycle is, that tells you what the computer is doing. To see if the MCS is working you can drop a little coffee stirrer straw in the bowl vent tube. you can see or feel it bouncing if the MCS is working.

Recall that the duty cycle is checked on the 6-cylinder on the meter.

IMO it's unlikely that something suddenly went wrong with the internals of the carb or the wiring harness to the computer.

Need to check throughly and carefully for a vacuum leak before launching off on a major repair that may not end well.

Tom
06-20-2018 04:56 PM
Maniacmechanic1 https://www.summitracing.com/parts/hly-0-80770
06-20-2018 04:34 PM
Maniacmechanic1
Quote:
Originally Posted by hamerDown View Post
This Car is wearing me down...not looking for a Pity Party or Sympathy from anyone but, I'm 60 years old with a busted-up body from construction, my soon to be 90 year-old father is in a Nursing Home on Hospice, I'm the ONLY one dealing with his house, his bills, his meds, doing his laundry and everything about him. I run to the Nursing home sometimes twice a day, run to his house to collect bills then make sure they are correct and pay them and make sure no one broke into his house (lots of building/construction tools and materials). I also deal with my own house, bills etc-etc-etc and now this verry annoying Vette issue...and if, my Diesel Truck takes a crap I'm, screwed.
I only have a little bit of time to try to test this and that on the Vette in a 9' wide garage that I can't even open the doors all the way...I've been waiting for a fella I know to let me borrow his older Snap-On Brick Scanner and hoping he has the needed muiti-1 connector that will reach down into the ALDL. But it appears him getting back to me is not his priority....I'm mentally and physically drained.
Holley 4 bbl
770 Cfm Street Avenger.
Electric choke.
Be my choice.
06-20-2018 03:54 PM
hamerDown
Quote:
Originally Posted by Maniacmechanic1 View Post
Cliff is Ok.
Has a website Forum just for Q-jets.
He works alot.

Pontiac Drag racer too on the street.

Be nice if you can ger that Q-jet working right.
This Car is wearing me down...not looking for a Pity Party or Sympathy from anyone but, I'm 60 years old with a busted-up body from construction, my soon to be 90 year-old father is in a Nursing Home on Hospice, I'm the ONLY one dealing with his house, his bills, his meds, doing his laundry and everything about him. I run to the Nursing home sometimes twice a day, run to his house to collect bills then make sure they are correct and pay them and make sure no one broke into his house (lots of building/construction tools and materials). I also deal with my own house, bills etc-etc-etc and now this verry annoying Vette issue...and if, my Diesel Truck takes a crap I'm, screwed.
I only have a little bit of time to try to test this and that on the Vette in a 9' wide garage that I can't even open the doors all the way...I've been waiting for a fella I know to let me borrow his older Snap-On Brick Scanner and hoping he has the needed muiti-1 connector that will reach down into the ALDL. But it appears him getting back to me is not his priority....I'm mentally and physically drained.
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