I have an 87 Trans am with a 4bbl Rochester Quadrajet carb on it. I had to replace the water pump recently and when i started it back up I realized that something was wrong (I belive it's been a build up to this). The car lacks serious power behind it, and it does this through the whole driving speed. The strange thing about it is that if i'm going at a good speed, the engine runs fine. The problem is whenever I stop and idle for a few seconds, the engine goes form about 750 rpms to close to 500 rpms, and when i start to go the engine runs rough. I was told to check a couple of things and was wondering if anyone had any other ideas.

1. Check timing
2. Check carburetor float (under the assumption that if the carb loads up while sitting the float may be stuck letting fuel into the bowl when it's not needed, loading the carb)
3. Check choke

For the choke I have no idea. How would you check the choke on a 4bbl Rochester Quadrajet with an electric choke? (is that even the proper carburetor that the car came with?)

Does anyone have any other ideas? or if you think which of these are more likely?

Any help is greatly appreciated!

 

The carbureted cars had a Rochester quadrajet from the factory. U.S.-delivered cars had a computer controlled q-jet. If yours is stock U.S.-delivered, it should be the computer q-jet. If so, are you getting an SES light?

Easiest way to verify the choke is: With car cold and not running, remove the air cleaner (at least the lid). Open the throttle a little (1/4-1/2 open is all it should take). The choke, the butterfly covering the front "barrels", should snap shut when you open the throttle.

Start the engine. The choke should open slightly (opened by the "vacuum break" or choke pull-off as it's more commonly called. In the next few minutes, the choke should gradually open until it is straight up and down after no more than 5 minutes. The idle speed will increase gradually as well until you open the throttle a little.

The carb won't "let" the engine run properly if there are ignitions problems such as fouled or worn out spark plugs, old/cracked spark plug wires, worn distributor cap/rotor, or mis-adjusted timing.

 

Here is where we run into a problem. The SES indicator is on. I see how this could mean a problem for the computer controlled choke. The only problem with figuring it out is that although the SES indicator is on, there are no error codes. I've done the jump from diagnostic to ground, but the light doesn't even flash a code 12. Instead the light stays lit

 

check your choke system,also the car should not be at 750 after it has warmed up, so i would say for sure to check your choke

 

I may have phrased myself wrong (my jargons probably off). Just to clarify, it "idles" at 750 when in drive but stopped. In park it idles at 1200. Hopefully that clarifies things.

 

The choke isn't computer controlled.

Are you sure you're jumping the right terminals?

 

Absolutely sure. I bought a repair manual and it had this test in it. I checked to make sure everything lined up like the picture (notch at the top) and jumped A and BM which happened to be the top right two. Is this correct?

 

And you connected the jumper with the engine off, and then turned the key to the on position without starting the engine?

 

Yessir, and instead of getting any flashes or pauses the light stays perpetually lit. I've searched and have found no solution. After this didn't work I took it to autozone (they do free readings... Its usually a hit or miss with older cars) and no codes could be pulled, there was just an "error"

 

If the computer isn't operating, it would definitely lack power.

The computer power wire runs along the frame rail to the battery. Any chance that was disturbed during the water pump change?

 

I checked the battery and two wires come off the positive terminal (which I assume supplies the power) and there are two wires, one goes to the alternator and an orange wire that I haven't traced back. Off the negative terminal, into a plug that then runs through an insulated wire by the engine. I don't think either of those is it. I will put a picture up later

 

Scratch the sending pictures, the orange (guess it was once red) cord going from the battery is connected to the ECM power harness. Is this "orange" cord suppose to be like an elastic? I literally feels like it's a bungee cord. I don't see how an electrical wire could be in it

EDIT: After doing a little searching I noticed that the end of the cord closes to the battery is thick and full of electrical wire, but towards the center the cord has turned stretchable and thin. I'm willing to be there is no wire in that area, meaning i'm getting no power to the ECM/computer? I see this as being a problem. Is that cord easily replaced (e.g. Cut and bug)?

 

Sorry for the triple post, but something has come up. I fixed the wire that connected the ECM to the battery. When I did the jump I got the code 12. I disconnected the jump and started the car, but it stalled. I had to keep the gas pedal depressed to keep the engine from stalling out, and the second I stopped the engine began to stall. I disconnected the clip that went from battery to ECM and the engine started up and did not stall.

Is the ECM choking out the carb?
What is my next step?

 

if memory serves me right that wire is a fuseable link wire and it was stretchy because it burned inside if insulation due to circuit over load.DO NOT hard wire this circuit.visually check harness for being pinched to ground near your water pump repair and i think youll find the problem.hopefully it didnt damage ecm

 

Yeah I hooked the circuit back together with another fusable link so if it did short it'd just burn up again... I hope anyway



So I have ANOTHER update! (sorry for all the multiple posts!)
I hooked the ECM back up and when I turned the key to the ON position, I heard some clicking. After doing some investigating, I found there was two different clicks, and each was coming from a separate connection. I have attached two pictures of where the clicking is coming from.

The one on the carburetor is coming from what I believe to be a solenoid, but don't know what it attaches to:





The other one is on the passenger side of the engine, I'm trying to find out exactly what it connects to, but as you can see, it's beyond the carburetor, and in the very back section of the engine, passanger side. Any ideas?





Any ideas? All help/suggestions/criticizm is greatly appreciated! (Also, you don't have to spoon feed me, lead me to the water, i'll drink

 

The connector on top of the carb that you have circled is the Mixture Control Solenoid. It'll click for about a minute after you turn the key, and continuously while the engine is idling.

Did you take that picture with the engine warm or cold?

 

top one is mixture control solenoid bottom may be egr solenoid?if aldl is jumped w key on it is normal for these to cycle i believe.does it start and run w ecm wire hooked up now?

 

Warmish? The car was probably running for four minutes before this picture was taken.



Still does not start. I was, however, able to force it to start (pump, pump, start, pump), and it did keep going on it's own for probably 30 seconds before it stalled again. I don't believe ALDL was jumped when I noticed these clicks, I will try it both ways (ALDL jumped, ALDL open) and report back.

 

I tried it both ways, and the clicking of the second picture doesn't happen when ALDL is open, but does click when ALDL is jumped... So I hope that's normal.
But what is the reasoning for the car stalling when the ECM is connected?

 

that is normal....does it just stall at idle and run normally when revved?does it still stall when engine is fully warmed up?

 

the biggest thing that happens is mix. control solenoid does not function w/o ecm powered up .this causes solenoid to default to open position causing rich condition.this could be compensating for vac. leak or just choke not setting when cold and when ecm is powered up and solenopid functions too lean and engine stalls.

 

Well like I said, the car runs when the ECM isn't powered, but does run rich... But when the ECM is powered the car stalls... So is this a problem with the choke and/or solenoid?

I took you last post and made an experiment out of it.

Fist I unhooked the ECM and ran the car to operating temperature
I then shut off the engine and hooked the ECM
When I started the car back up it didn't stall, but it idled between 750-600 rpm's
I noticed that the car sounds better and runs well when revved (rpm's stable around 1500)
I then put the car into drive, and it stalled
I then restarted the engine, and gave it a small bit of gas before setting it into drive, and let the car go. The car did not stall, and drove well... With a few exceptions

1. When I stopped at a stop sign, the car idled at 500 rpms. When I brought it back I left it idle in park for about a minute and every so often it tried to stall but quickly came back
2. When I got up high in speed and rpm's (speed was between 40-50mph and the tach was at 1.8-2.0 rpm's) the tach went down to about 1.2 rpm's and ran rough with the accelerater depressed... It jerked at a periodic rate.

Sounds like fuel mixture to me... What do you guys think?

 

at this point id be looking for a vacuum leak and if i didnt find any id be rebuilding the carb.also pull vent hose off carb and make sure no fuel in it . seem to rmember having problems w purge valves on these motors.

 

I was hoping a rebuild would be my complete LAST resort... So I guess I'm going to look for a vacuum leak first (yeah... good luck with that one) and check that vent hose.

Anyone else have any advice before I take this for a rebuild?

 

Check the EGR and EGR solenoid. When those go bad it spells real trouble at idle. You know stalling, and sputtering, but once you get going she will seem to run okay, but probably surge some. Also check for vacuum leaks. I had to re-plumb my entire engine bay on my 87 Formula, she is 23 years old. The hoses get hard and crack apart. Just my two cents.

 

In the picture of the carb above I see what looks like electrical tape around a vacuum connection that I believe should run to the thermac stove on the snorkel of the air cleaner. And I agree about changing ALL vacuum lines if you know they are old. Small cracks in a few can add up to a substantial leak. After buying my '83 last summer I changed all the lines in mine and it was a night and day difference.

 

Looks like it could use some cleaning up. What is your fuel pressure i wonder?

 

i agree carb rebuild and check fuel pressure, and egr

 

Is there a test for the EGR/solenoid or is it just a replace matter?

I'll have to hook up the pressure valve and look

 

When did you acquire the '87? A PO could have tweaked the carb so that it would run 'decently' with the MCS inop. In this state it would have run rich, and with any vacuum leaks, likely idled high. The curb idle speed may need to be reset.

The ECM also controlled ignition timing and when not working the ICM would have been working on a default, weak timing curve (not really a curve at all). The timing may have been adjusted mechanically to compensate for this.

Test your EGR: get it idling and with your fingers pull up the diaphragm underneath the EGR valve. This will open the valve, allow exhaust into the mixture and should cause the idle quality to worsen. If there is no change it could indicate that the EGR valve is stuck open (or it could be broken/passages clogged). If it stumbles, your EGR is NOT causing your idle problems.

Check your timing. After replacing your plugs, cap, rotor and wires: Adjust your timing with the four-pin connector on the rear of the dist disconnected and set it to between 0 and 4 degrees advanced (you may have to bump your idle speed up to do this, it won't want to run as well with the plug disconnected). Go ahead now and use a little bright paint on the thin groove in the balancer so you can see it with the timing light. Re-connect your plug and verify with the timing light that the timing is near 20-22 advanced at idle and that it increases with RPMs. You won't see any marks there but it's important to ensure that it's advancing properly, not necessarily exactly how much it's advancing.

Cap every vacuum port (except for the VAC sensor line that goes to the rear of the carb-should be a small, hard plastic line) and set your idle speed. Re-connect them one at a time to see if any of them reveal an idle quality change. Drive it and see how it does.

The plug over the IAB adjustment, on top of the carb, has been removed. Someone has likely played with this. You'll need a dwell meter to properly set it AND determine whether your ECM is going into open loop. A scanner that reads operational data will work as well. Go thru the above, post back and find a meter. We can walk you thru checking/setting your TPS and IAB.

 

You, my good sir, are amazing. I bought the '87 in June of 2009. Unfotunately it's at a steady rain (read as: a downpour) right now, so I'll have to get cracking on this tomorrow. Should I do all this testing with the ECM engaged or disengaged?

 

Try to do everything with the ECM powered. With it off the MCS will stay in the top position with no restriction to the primary jets. All that extra fuel isn't good for it.

 

So far I checked the EGR and the timing.

I checked the EGR with the ECM on. After pressing up on the diaphragm the car (which it was already sputtering) ran even more rough and stalled out. So i'm guessing the EGR is ruled out

Next I checked the timing with the ECM off (in Drive, 500 rpm, as stated on the hood), and I get this:




I have no idea what the timing is. I never saw this type of marker before, but the white line is where the timing was.
Trying to time with the ECM on appears to be a losing battle.



EDIT:

I got some help from a neighbor to give the engine a bit of gas to keep it at 500 rpm in drive with the ECM hooked up... Bad news Bears
When I went to time it the mark was nowhere... Not anywhere in the markers and also nowhere in my field of view (wasn't very much). Is this even possible?

 

What you're experiencing is normal. The ECM will add timing to the base amount resulting in around 22 degrees of timing at idle. That's why you set it with the four-wire connector disconnected from the back of the distributor. This connector is the ECM's communications link to the dist (and timing).

Yours looks to be about 6 degrees advanced base timing. The bigger notch to right is 0 degrees. I'd leave it there for now. Your '87 will have a knock sensor circuit. After you get it running you may find that slightly less timing will net you more mileage (and better performance). Too much timing and the KS may kick off and pull too much back out.

 

Two possible causes down...

Just to make sure i'll be doing this right, there is a sticker on the hood indicating vaccum routing (I believe, correct me if i'm wrong). Are these the holes i'm suppose to plug?

 

Just plug all of the ports on the carb, with the exception of the rear port bottom of carb that goes to the vAC sensor and the single line coming off the manifold behind the carb (don't need to plug the bowl vent, which is on top,in front) . The large booster line center rear of carb can be capped with a plug/bolt in the rubber hose that stretches to the brake booster.

You can plug each with a small piece of appropriately sized hose and a bolt in the end or use one of the vacuum port cap kits that come with different sizes/colors of caps.

While you're there go ahead and check the turns out setting on the IAB. Count number of turns to seat and if it's not around 3 or 4 go ahead and set it at 3.5. Same with the idle mixture screws if there tamper proof plugs have been removed. Just recort all existing settings so they can be restored if need be. Let us know where you found them at, it's likely someone before you dickered with these.

 

I believe the vaccum test was unremarkable to say the least. With the ECM off, the car ran rough when I unplugged the ports, and ran fine when I put them hooked them back up to their proper spots.

Unfortunately I do not know what an IAB is, or where the idle mixture screw is. I read my Haynes repair manual and have found nothing of these two parts. Care to give me some reading material?

 

Pics of the inside parts:

https://www.thirdgen.org/forums/carb...-ccc-qjet.html

Sticky at top of forum:

https://www.thirdgen.org/forums/carb...e-rebuild.html

Oldie but goodie:

https://www.thirdgen.org/forums/carb...tions-lg4.html

Current thread:

https://www.thirdgen.org/forums/carb...uild-help.html

 

Question: Wouldn't it be nice if this was a sticky?
Answer: Yes, it would.

"Pics of the inside parts:

https://www.thirdgen.org/forums/carb...-ccc-qjet.html"

 

Added to the "welcome to the carburetor forum" sticky.