GNX rough idle

GNX-481

New Member
Hi Guys,
I was hoping someone can point me in the right direction. I am the new owner of #481 and it has 467 original miles. I am struggling with a rough idle with no codes thrown.
I did adjust the TPS which was at .034, I adjusted to .047, seems to have done a little, but not much.
I did notice a wire looks torn from one of the sensors, but I don't know if this sensor requires only two wires. I have attached photos.
also, I have purchased an Innova scanner to attempt to get LIVE DATA, but It turns out that even though its an ODB1 scanner, it doesn't support the 4th digit VIN (G). Does anyone recommend the most lest intrusive scanner which we dump the LIVE DATA? I have seen one which requires modifying the ECM which I am not interested in doing.

I have attached photos of the sensor, its right directly under the water pump to the left and above the oil filter.

Any help here would be greatly appreciated.

thanks
-tom
 

Attachments

What Chip is in it.If it’s a Stock Chip take it out and Order a Chip from Turbotweak for a Stock Car.I am Assuming that a GNX with that mileage is Stock.
 

GNX-481

New Member
Thanks Chris, yes nothing in the car has been touched original plastic still on the seats from dealer. Do those chips just go bad like that ?

Do you think the sensor I posted with the torn wire may be the issue ?
 
That Chip from 1987 if it’s the Stock Chip is no good to run on today’s fuel way too much Timing in it.Go on Turbtweaks site follow how to order a chip you should get a Chip Injector package he has that combo.I would go with his 42 pound Injectors and 93 Octane Street Chip.Remove the Chip in the ECM and see what it says on it first,you may already have one of Eric’s Chips.
 

X Ray

The GNX changed my life!
The wire is ok....it was cut from the factory (ASC) to support the oil pressure gauge in the dash.
Get a scan master to help with the diagnoses.
With so little miles on the car I would change the gas filter and make sure no old fuel is in the tank.
Also when you get the Scan master have him get you a new chip....We have learn a lot over the years in chip development.....but make sure to keep the original.
See attached link...

 

Anthony P

sharing knowledge with those who care to listen
whoa, whoa, whoa.....FULL STOP....

481 is a museum piece with only 467 miles. highly doubt it will become a driven Buick. don't mess with the chip. that is not your problem.

I hope the TPS voltage values were a typo...set the TPS to .42V to .44V with key ON, engine OFF. verify while sitting in driver seat that WOT TPS voltage is about 4.4 to 4.6V. actually, I believe anything above 4.0V, the ECM enters POWER ENRICHMENT mode.

start car and let warm up to operating temp about 160F. now in CLOSED LOOP. verify IAC counts to be between 10 and 30 and not bottomed out at 0. adjust IAC via spring locked screw on throttle body - it's under the silver colored vinyl cap - driver's side. when adjusting IAC, have to go back and double check TPS because the adjusting screw to set IAC moves the throttle plate thus changing TPS value. Where you noted setting TPS to .47, is high. At about .48V signal, the ECM thinks the car is driving. so get the TPS back to .42 to .44 as a start.

with engine running at idle in CLOSED LOOP verify the MAF is reading airflow....should be about 8 at idle of 775 RPM. verify the flow rate value increases with increase in engine RPM.

since this is a concours example, I'm more believing that old gas is a problem like Rick (X ray) noted. so fresh gas would be great. a new fuel filter is suggested.

if the tank is full, locate the fuel pump prime wire connector, black which is taped with a green connector single wire to the A/C line at the pressure switch behind the compressor. The green connector is for an external tachometer hookup with GM's tools. using alligator clip jumper wire, the fuel pump can be operated by making the connection at the rear of the alternator and the black connector. remove the fuel rail cap and remove the schrader valve on a depressurized system. attach a hose and jump out the fuel pump to fill some cans to drain the tank.

additionally, even if fuel stabilizer was used, I'll bet the factory pintle style injectors are fouled from sitting. the image below shows how brand new stock Bosch injectors flow after only going a few hundred miles over a few years.
20190524_125948.jpeg
after cleaning, the did all flow much better, but were less than the calibration injector on the LEFT - but within tolerance.
20190524_153917 copy.jpg

so, injector cleaning maybe something for a to do list, but TPS, fuel filter and fresh gas should be done first.

X ray covered the "cut" wire at the oil pressure sending unit. he would know, he worked on all 547 of them.

as far as scan tools go, I use the Auto Xray 5000 and 6000 models. it has been discontinued for a bunch of years but can be found on ebay and the like. I believe Actron bought the Auto Xray product line and immediately discontinued it to eliminate the competition. the updated product available today is the Bosch-Actron CP9690 LINK to product at JEGS => Bosch-Actron CP9690: Elite AutoScanner Code Scanner Kit OBD-I, OBD-II and CAN | JEGS

it's the same price as a ScanMaster and gives more info and can record data and show freeze frame data for all the parameters pulled from the ECM. covers all the ODB-1 manufacturers (GM, FORD, Chrysler, Toyota) and ODB-2 and CAN. I'm not a fan of the Buick only ScanMaster - don't want anything mounted around the dash that didn't come that way from the factory.


if you're gonna take the plastic of the seats and steering wheel and pile on the miles taking a concours car to driver, then consider a TurboTweak chip. HOWEVER, I highly doubt someone would do that to an investment grade vehicle.

attached is a spreadsheet I made for the GN with a factory PROM chip. the available parameters would be the same on a GNX, although the PROM id checksum will not be a value of 144 on a GNX. it's an easy way to record values as you work thru the matter at hand.

as I've been typing for a bit now, there may be more comments since X ray's response.
 

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samgauto

Member
Nice info here. I never noticed the clipped wire on that sensor...and always wondered what those 2 connectors were for behind the compressor! I though most GNX's and GN's had a normal 'odd idle' sort of like an engine with a higher lift cam. But I guess depends on ones thought of how rough it really seems as opposed to what normal is. My 8k mile GNX does not have the smoothest idle either. If you start it cold and don't let it run a few minutes and put it in reverse too soon it will even stall on occasion but restarts with no problem. I did clean around the throttle blade but reallly did not find it that dirty. (Back in the day it never hurt to clean the throttle blade deposits but Im not sure this engine really had that issue). But good info here. Just ordered that tool you recommded from Jegs and will check the datastream values.
 

GNX-481

New Member
Anthony P, Wow that's a lot of info, can't thank you enough.

Sorry, my bad, yes I set it to 0.47, it was at .34, I went thought the whole scale from idle (0.47, incrementally up to WOT around 4.6).
I will reset TPS to .42-.44.

Is there an easier way to get most of the fuel out ? there is a little less than 1/2 tank

I won't be able to check the other items until I get the scanner, should be by Thursday, I did get the Actron CP9690 (easy to find)
 

Anthony P

sharing knowledge with those who care to listen
Hi Tom, I'll take a step back for a moment. congratulations on your acquisition and welcome to the forum.

I think jumping out the fuel pump and using cans is easier than dropping the tank, spinning the lock ring and removing the fuel pump sending unit. gasoline weighs about 6 pounds per gallon - half tank => ~ 50 lbs. could fabricate a cradle putting woodworking or welding skills to use and adapt a floor jack or trans jack. having a tank with gas sit on your chest while on your back under the car disconnecting the hose clamps from the standpipe lines isn't the best way either. trying to avoid unnecessary work.

Curiosity would have me drop the tank a some point just to confirm what the inside looks like and the condition of the fuel pump sock. Also, if the gas is really old and has jelly settling on the bottom of tank, that needs to be addressed. that task is much easier if the tank is run down first.

But with your example, I'm trying to avoid unnecessary work and not add any tool marks to indicate someone has been fiddling with something here as a keen eye would notice.

So I circle back to TPS adjustment, fuel filter, letting the pump drain the tank and some fresh gasoline.

@samgauto make a very good point. until the engine reaches normal operating temp, the idle can sound lumpy and experience RPM hunt of a few hundred above or below controlled idle with the factory PROM chip - turbo Regal models or GNX - they all do it. As noted, if start cold engine and immediately shift into gear, engine can stall. Also, cold engine start, shift to drive before reaching operating temp, depress accelerator, engine will hesitate and stumble as car begins to move. All do this. No issue if engine temp up to 160F - 170F before you shift into gear and drive.

It's the above that sam noted to be aware of and to confirm that is not your question at hand. Perhaps all that is needed is a TPS setting adjustment as a secondary discovery.

Change fuel filter. OK. what records from previous owner? Plus visual inspection of fuel filter will say a lot. brand? The original fuel filter was ACDelco GF481 (GM 25055052). The GM 8-digit part # has changed many times over the past three decades as more car models were added to the fitment list. An original filter had a silver label with a black border as pictured below.


The GF481 (GM 25055052) was replaced with 25171792 on December 1, 2004 for the U.S. market; citation here => GM 25055052 Filter, genuine OEM part

GM 25171792 is crossed to ACDelco GF652. Info is now directly printed on filter body. reference images can be found on ebay. On the GF652 ebay image below, the third line printed shows the date of manufacture. 13126 is the date code; 2013, the 126th day. So you can determine how old the filter is, but it's unclear when it was installed.

If it's an original fuel filter, not a bad idea to change it. SAVE THE ORIGINAL! for your car with its pedigree, saving service parts is key as I see it.
 

Attachments

GNX-481

New Member
Hi Anthony, Here is a picture I just took of the fuel filter, looks original to me, doesn't even look like the bolt was cracked :)

I will have the new scanner tomorrow for more data.

In the meantime, do you recommend any fuel injector cleaner I could try ? or a fuel additive that may help ?

thanks
-tom
 

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Anthony P

sharing knowledge with those who care to listen
Hi Tom, wow, that is the original fuel filter from the assembly line. I was kind of thinking that on a 400 mile car. on the right side of the label is a printed 5-digit #. that is the date code and shift #. can't read your #'s exactly but format goes like this....

on my example above, #'s are 01251. that is the 012th day of 1985, 1st shift.

I'm not a big fan of the fuel system cleaners that are added to a tank of gas. I don't know that they do anything. some opinions are that seafoam does something, but I just don't know about that.

what I have done for on-car injector service is the run-rite setup. add their product to a cylinder that is hung like an IV-bag. there is a metering valve to control the drip rate into the line. the line is attached to a vacuum port via a Tee. engine is run at 1500 RPM for about a half hour to take in the product. but I can't see the investment in that setup for periodic use.

My opinion is the best way to clean and flow check injectors is to remove them, ultrasonic cleaning and then flow check on an injector machine. the individual flow testing will show if any injector flows a tad bit more than the others. it's the ones that flow a tad bit more than the others that you'd want to install for cylinders 5 and 6 as those two are the ones that flow the most air. Several years ago, Mr. Richard Clark flowed intake systems. read about it here when you have time...

interesting numbers

tons of places clean and flow injectors. you can find someone close to you and do them locally. Mr Chuck Leeper here does them as part of his business.

So here's a conundrum. A concours example is a static display as a museum piece. it's not even started. so depending what your plans are for the car is something to think about before wrenching on it to remove the coilpak/ignition module stuff, the bracket for the 3 cables on the doghouse, and other stuff to permit the removal of the fuel rail to access the injectors.

today's ethanol based gas is tough. those stock pintle injectors will foul in time just from sitting. in another 3, 4 or 5 years, they will have to be pulled again for cleaning and flowing. Sometimes an injector will stick closed and flow zero. but tapping on it lightly while its pulsing in the ultrasonic bath will fix a stuck pintle. switching to a disc type injector eliminates the inherent issues of ethanol based fuels used with pintle type injectors on engines rarely started. I typed this up recently for another fellow here: Bosch 237 Regulator

it all comes back to the question of wrenching on the car to service it to get it running properly or not touching it...to avoid repeating the same work every few years to clean injectors, I'd consider swapping out the original Bosch units for the 30pph Lucas 5207009 disc injectors. no modification to the ECM chip is needed since they flow as stock. more info here: Racetronix-Delphi_Injector_Sale-42s

lots to consider as you review your plan for the car...
 

grass doctor

Dream Catcher
fuel system cleaner in a container ...is really only for preventive maintenance and rarely will solve any real issues ...from the research ive done ...the only one really worth using is chevron Techron ...for the price ....but nothing beats having your injectors professionally cleaned....@ chuck leeper....now there is also the 33 year old maf sensor that might need a cleaning and can cause rough idle situation ...but they are delicate and require the use of only spec'd maf cleaner CRC brand...but just another preventive maintenance thing to think about ....I would probably drop the tank just for visual inspection of what you could see inside just to be sure ...if you dont pump it out like Anthony spoke of ..still good idea to have some extra hands and just have a bucket or something to set on initially as you position out fully ....so much great info ...my car was original when I got it and idled high until warmed up ...would say rough ...but still not to my liking...so I had Eric make me a chip for stock injectors and 93... ...but I also put an lt1 maf sensor on it with translator..probably not wanted on such a pristine example of a classic ..but anyways.. it made a noticeable difference on start up an idle...I also cleaned my IAC...and did the hard reset...and got the tps right and idle at 800-850 rpms.. ...and it ran like crap for about 50 miles until the ecm relearned ....but I have read on so many threads that these cars have had idle issues until warmed in stock configuration....anyways just my 2 cents
 

1986 Buick GX1

GX1 #001 [The One and Only]
When my car was new, with the stock chip It didn’t run very well until warmed up as mentioned above.
On cold startup it would go to high idle for 20 or 30 seconds. The idle would come down, the car would run lean and stumble. It would go to high idle again and repeat the process 3 or 4 times until it was warm enough to idle smoothly.

If I were going to drive the car at all, even in and out of the enclosed trailer, I would change the chip (easy enough to do).

On a daily driver I had a slight shudder at part throttle acceleration like a cv shaft was on its way out. It ended up being a slight misfire.
The only in tank fuel system treatment/ injector cleaner that worked for me was BG 44K, although it took 2 tank fulls to clear it up, I didn’t have any problems after that.

 

grass doctor

Dream Catcher
Hi Anthony, Here is a picture I just took of the fuel filter, looks original to me, doesn't even look like the bolt was cracked :)

I will have the new scanner tomorrow for more data.

In the meantime, do you recommend any fuel injector cleaner I could try ? or a fuel additive that may help ?

thanks
-tom
where are you located ...might be someone close ...to give you a hand ...if you d like ....
 

GNX-481

New Member
@grass doctor , I am in San Diego, Rancho Santa Fe to be exact.

@Anthony P - Received my Actron scanner today, worked like a charm! thanks again for the great guidance.

I recorded 10 frames of data, interesting info, let me dump some of it here, wondering if there is anything to conclude from these time slices.

Frame 0 (time 0.0):
BLM-127
Coolant -122
EGR % -0
RPM -950
Exhaust 02 - RICH
IAC position - 75
LOOP status - closed
02S(mV)-440
02S CroosCnts-137
spark adv (degrees)-42
TPS-.43


Frame 3 (time 7.9):
BLM-127
Coolant -123
EGR % -0
RPM -925
Exhaust 02 - LEAN
IAC position - 75
LOOP status - closed
02S(mV)-573
02S CroosCnts-249
spark adv (degrees)-41
TPS-.43


Frame 10 (time 26.5):
BLM-127
Coolant -130
EGR % -0
RPM -975
Exhaust 02 - RICH
IAC position - 77
LOOP status - closed
02S(mV)-670
02S CroosCnts-228
spark adv (degrees)-38
TPS-.43
 

grass doctor

Dream Catcher
it will always be rich or lean... off the narrow band sensor...in closed loop...the tt chip is an open loop idle ...which once it learns its idle it will be set per what Eric programs for fuel...
 

GNX-481

New Member
it will always be rich or lean... off the narrow band sensor...in closed loop...the tt chip is an open loop idle ...which once it learns its idle it will be set per what Eric programs for fuel...
Ok this is all stock, with the stock chip. Just wondering if that was normal I guess it is.
 
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