grand prix 2+2 help

[garyk1970]

i dont know where to post this ,but i know my bro's can help.my 1986 pontiac grand prix 2+2 ,5.0 v8,has a computer monitored/controlled quadrajet carb.
i got a code 21 which is a tps code,went to test tps(its located IN the carb)and unplugged tps plug to test for reference ground (good)and positive(5.0v),has both and i went ahead and tested output lead(just curious)and has 4.7 v there too!?remember i unplugged the tps,should not be any voltage on that(output to computer) lead,right?same readings plugged up. i need to take a quick look at a wiring diagram to see if another sensor could be causing voltage to "feed back" through computer.tried another computer and same thing.car completely stock.any guesses?link to a diagram?

 

[zeus87gn]

Hey you wire nut! How goes it?

Question...did you have the key on or off?

If you had the key on, you should be correct. Probably a high impediance input circuit to the computer. Also could be a reverse voltage type circuit that has a voltage there because it it trying to read current? The TPS is only a variable resitor. Don't really know without the diagram that I wouldn't know where to find. What resistance did you get on the TPS itself?

If you had the key off, you have problems.

Call me if you want, I just got Zeus all polished and looking for an excuse to go crusing!

 

[garyk1970]

hey dude! im heading your way friday,if i get all the jobs done, ill call you and hopefully visit another buick nut.....ive got your #"s in my email,right?

tests done with key on.cant get any reading on the tps itself either,looks like its stuck.....im gonna drive it some (its been sitting for four years).o2 went bad,replaced it,maybe something in fuel,or bad gas (thats not far fetched).just didnt know if voltage on signal lead is normal,everything i know says that lead should show 0.0vs unless tps is in operation.

 

[zeus87gn]

Yea, you should have my numbers. I'll send you another just to be sure.

If you can't get a resistance reading, static or in movement, it's probably gone. Voltage present at the signal wire plug with it removed(?) could indicate a short. It's been sitting...do you have rodent problems up there?

Oh, have you checked the signal wire for short? I.e. key off, plug out, resistance measured from pin to ground. You do have a DMM - right?

I haven't seen one of those 2+2's in years...since I was i kid in Ill. Will it run well enough to make it to Stsbo? We can check it out. Friday daytme I will be in the office, friday evening I will be home. Call me.

 

[garyk1970]

yep,but its seems to be shorted to postive.that why i suspect some kind of feedback.unless the tps test (signal lead)is done in series?im stumped.when it comes to driveablity issues,i have alot to learn.no shorts per say.im thinking the other day i took a drive and floored it and held throttle w/o for awhile,thats when the tps probably got stuck.no rodent probs here ......i can drive it cross country if i wanted,the cel came on friday,so i checked and had a 02 code,checked it,looked original(70k miles on car)i replaced it and took it out to "blow it out" and thats when the tps prob came in,not sure because i didnt clear any codes out before that.
would like to drive it,but will be in the good ol work van.ill call you friday....im gonna put car back together and drive it for a couple of days and see if tps unsticks itself untill i can look at diagram.

 

[zeus87gn]

No rodent problems? Dude, we live in SE Ga. :biggrin:

Maybe you broke the contact in the TPS. I'll bet it doesn't dome back. I hate quadrajunks. My brother had one burn up his olds.

Yep, definetely need a schematic. You could be right, and the signal is fed from the computer. Wait, if that were so it would be a 2 wire device. There may be more here than we are aware of. If we can get together one weekend we can probably figure it out.

 

[Searcher]

Plug it in and get the readings that way. You'll have to figure a way to back probe the connector with something like a stretched out paper clip, or a pin through each wire. While effective, that method is not recommended due to internal wire corrosion potential later. Circuit voltage readings may not be valid with an open circuit.

Anyway these TPS's were a major problem back in the day. About every M4MC carbed GM I worked on that had any codes at all, a bad TPS was always in the mix. If you look at the acclerator pump arm you'll see a green plunger contacting the arm from below. That is the pushrod that goes to the TPS. You gotta pull the carb top up to get the TPS out which can be done with the carb in place, but with the age of this car the top gasket is likely to tear in a bad spot unless you're REALLY careful.

 

[garyk1970]

Plug it in and get the readings that way. You'll have to figure a way to back probe the connector with something like a stretched out paper clip, or a pin through each wire. While effective, that method is not recommended due to internal wire corrosion potential later. Circuit voltage readings may not be valid with an open circuit.

Anyway these TPS's were a major problem back in the day. About every M4MC carbed GM I worked on that had any codes at all, a bad TPS was always in the mix. If you look at the acclerator pump arm you'll see a green plunger contacting the arm from below. That is the pushrod that goes to the TPS. You gotta pull the carb top up to get the TPS out which can be done with the carb in place, but with the age of this car the top gasket is likely to tear in a bad spot unless you're REALLY careful.

i tried with it pluged in too(got a older dvw with large sewing needles soldered where the probes used to be)and got the same readings.looks like its stuck a wot.i recently rebuilt carb and I knew i should have replaced sensor since it was inside,should be able to pull top off since rebuild was only a coupe months ago.thanks for the tip.

 

[Searcher]

Just don't forget about the two carb top screws inside the primary air horn, and the two just behind that same air horn, close to the air cleaner stud.

 

[garyk1970]

searcher, i got tps in carb (needed four hands at one point during reassembly!!)now it reads correctlly,no codes.old tps completly dead,no readings at all,internal open.

got to checking everything out,and once engine was warm,tried to get secondarys to open,no dice,4bl wont open.i know this car is extremely slow,but i knew something was not right.if i play with choke linkage(w/engine off)butterflys will open (looking for stuck linkage)anythink to look for,ive looked and looked,no binding,etc that i can see.theres a whole lot going on there.looks like front vaccum brake isnt releasing,unless i unhook vaccum from it.that looks like it wont let the top secondary butterflys to open.im sure bottom isnt opening either...any ideas to try would be great,i have a haynes tech book and nothing on trouble shooting if secondarys dont open.

in the meanwhile,im going out and replacing the heater core that just busted while i was "testing" the 4bl.thats about the only thing i havent replaced during the resto.

 

[Searcher]

If it ain't one thing, it's another

As for the secondaries there are a couple of things to check.

The secondary throttle blades have a choke activated lock-out. It's a small linkage on the right side that engages a silver pin that goes through the secondary throttle shaft. You can see a flat spot on that pin where the linkage is to hit. Sometimes the linkage arm sticks and doesn't allow the secondary throttle blades to open since it only falls away by gravity. Or the choke doesn't open completely for a variety of reasons.

The secondary air valve shouldn't really open just sitting there winging the throttle. In fact, the choke pull-off is linked to the air valve specifically to slow the opening. Without the pull-off you tend to get sags in acceleration (bogging) when the secondaries open. GM hit the secondary air valve opening rate just about right, so goofing around with the pull-off and air valve spring tension tends to result in slowing the car down.

 

[garyk1970]

If it ain't one thing, it's another

As for the secondaries there are a couple of things to check.

The secondary throttle blades have a choke activated lock-out. It's a small linkage on the right side that engages a silver pin that goes through the secondary throttle shaft. You can see a flat spot on that pin where the linkage is to hit. Sometimes the linkage arm sticks and doesn't allow the secondary throttle blades to open since it only falls away by gravity. Or the choke doesn't open completely for a variety of reasons.

The secondary air valve shouldn't really open just sitting there winging the throttle. In fact, the choke pull-off is linked to the air valve specifically to slow the opening. Without the pull-off you tend to get sags in acceleration (bogging) when the secondaries open. GM hit the secondary air valve opening rate just about right, so goofing around with the pull-off and air valve spring tension tends to result in slowing the car down.

youre the man!! went out checked the choke,and it wasnt releasing after warm up(probably spring is getting weak) adjusted choke and viola,its got all four barrels for that nice wooommmm sound.now onto the heater core ,also found idle speed syl weak(not enough grunt to sligthly idle up w/ac on)gotta replace that too, i should buy stock in autozone.thanks for the info,
Gary

 

[Searcher]

...also found idle speed syl weak(not enough grunt to sligthly idle up w/ac on)gotta replace that too...

I have yet to see an electric dashpot solenoid that has the moxie to open the throttle on its own. Every one I've ever seen required the driver to crack the throttle a bit to get it to set. The ones that DO work like you'd think are vacuum operated, like the Idle Load Compensator in Olds 307 installs. Ford went to vacuum too on the old Central Fuel Injected cars and on the 4bbl equipped 5 liter Mustangs. I forget what Mopar did in this regard, probably nothing. Oh yeah, all Mopar had through that last gasp of carbs was a K-car that had either the awful carbed 2.2, or the worse Mikuni carbed 2.6 :bleah: Both used electric dashpots.

Replace it if you want, but I doubt you'll see a difference.

 

[zeus87gn]

So the TPS was gone. Good to see you got it working. Thanks to Searcher for the education. I'm glad someone knows about these carbs. I have only had experience with Holleys. Many varied opinions there. Got to do some fine tuning on mine anyway.

See ya Friday!

 

[garyk1970]

yep,searcher definently know his carbs.thanks for the info and the education.if i blip the throttle,the idle does stay up.ill leave well enough alone.happy to get idle down,4bbl's operational,and the deisel run-on stopped,thats embarrasing on to the dreaded heater core,ill be outside cussin' for awhile. not too bad,im just really tired of this car right now.

Zues,have you got the cooler iced up yet????(you can never really prepare too early???)searcher should come over and have a few on me.

 

[zeus87gn]

yep,searcher definently know his carbs.thanks for the info and the education.if i blip the throttle,the idle does stay up.ill leave well enough alone.happy to get idle down,4bbl's operational,and the deisel run-on stopped,thats embarrasing on to the dreaded heater core,ill be outside cussin' for awhile. not too bad,im just really tired of this car right now.

If you have (had) deiseling problems, you may have the timing off a degree or two. If the computer controls the curve, you may have to reset your baseline. Depends on what type of system you have mixed in with that computer. Ahh, the 80s...glorious transition years to port fuel injection.

Zues,have you got the cooler iced up yet????(you can never really prepare too early???)searcher should come over and have a few on me.

Heater cores are a PITA. AC drain holes are even worse. I have to do my van soon before my whole floorboard is soaking wet.

Packing it up tomorrow night, don't want the ice to melt!
Hope you got my email.
Call me if you get done early, I should be at the house.

 

[garyk1970]

zues, the dieseling probs went away when i fixed;inop 02 sensor,inop tps,got idle down,got choke adjusted,etc,etc.timing bolt still torqued from the factory.checking my mail now.

 

[zeus87gn]

Dude, just call me.
I'm at my desk.