What Would Cause This ?

Lockman

OH, OK .......Now I get it
On my ' 84 , she starts right up ( Always has... Lucky , i 've read ) , Idles pretty well. I 'll drive away slowly , until I see temps at about 175. then on a stop sign start on a 50 mph road , 975 RPM to about 1500 , very smooth acceleration. After that , from about 1500 to about 2500 RPM, she shudders like she's missing & then at about 2500 rpm & higher , she smooths right out again ? Goes right up to 55 - 60 mph 7 runs & drives well . The tranny seems to shift smooth , during all this . Whadda Ya'all think could be possible causes? Thanks , in Advance----Lockman :confused:
 

Lockman

OH, OK .......Now I get it
Yes, I replaced the MAF 2 months ago, with a Remaned OEM GM Part # 74- 7653 ?
Yeah, attached is a PDF download. Reads 6-7 at stop sign Idle up to 67-84 at driving rpm of ` 2300 -2550. Temp at ~ 185 Degrees.
Thanks for any further help you can give. I really rely on ya'all for your experience . I'm new to a Hot air .
 

Attachments

  • 4-13-2019 Driving Log Data.pdf
    576.6 KB · Views: 37

Lockman

OH, OK .......Now I get it
Thanks for the advice.... Any suggestions of where i could purchase a known good oem one ??? I have no clue ...
 
I think when I was browsing through GBodyParts.com I saw they had a reman one that is supposedly calibrated correctly. Might check there?
 

Lockman

OH, OK .......Now I get it
Well, OK............ I just ordered a new MAF from Gbody. 200.00 soots. ( The one I got two months ago was 75.00 from an old Buick dealership in Michigan ) Here's hoping . I should get it and install on Weds. I'm going to replace all vacume hoses , throttle body ' O ' Rings, & plug wires We ain't gonna know which fixes her up, but I'll let you know. Thanks for your support....
Richie------- Lockman
 

turbonut85

Rarely used member
Crap man...I don't Get on here much anymore and I just Saw this....I would Have sent you a stock one to try out....sorry.
 

Lockman

OH, OK .......Now I get it
I didn't know .Thanks anyway ....... The one I installed 2 months ago was in an old 'Federal ' box , with instructions from 1992. they said it was a Reman though. It looks to have a sort of ' venturi " on the inside, with a very fine screen. The original was same size throughout, with a much bigger screen. Almost like chicken wire ? Based on the numbers I was logging , I was getting only high 80's at almost wide open throttle. Do you think GoodBody's is reliable . If so, it would be worth it to me ( I hope i'm not wasting my Dough & Time.) I'm not racing this Rig , I just want it tuned & to run the best I can get it to the original running order, as it came from the factory ? Thyanks, again for your thoughts and help . I'll let you Know........
Richie------- Lockman
 

Lockman

OH, OK .......Now I get it
Hey Guys..... I'm try'n here ! GBody's ( Brian , Good Man, BTW ) is negotiating with the supplier ( Cardone ... The only rebuilder out there ? ) . It seems that they have been sending a good amount of faulty MAF's out recently. That might be the problem with the one I got on now , from someone else ? Anyway, I did change over all vacume lines and spark plug wires. I could not use the shaft seals that they sent.... way to large for my throttle body . I was glad to see the BLM values go down to 130, after doing the IAC reset procedure for the tenth time , in the last 3 months. I've got trouble with setting the newer TPS though. I get it set between .40 & .42 , take it for a run , or rev it and the voltage jumps up to about .49 and stays that way ? 2 questions : Are there possibly faulty TPS sensors for sale out there ? And.... Do Throttle body's wear out and get out of calibration over the many years ? ( I noticed mine's stamped with an 83 ? )
Any body that wants to advise or commiserate , would be greatly welcome.
1984 Throtle Body #'s.JPG
 

Lockman

OH, OK .......Now I get it
So.... It snowed here this morning ; 32 Degrees . I decided to post these pics of my data. I followed ( Exactly ) a reply that I searched on our forum that seemed to jump out at me . It may help other Hot Air guys too, I hope :

May 2, 2013
" Your IAC and TPS are probably so far out-of-whack now that it might be a good idea to start from scratch.

First, do the minimum idle air adjustment. This will also cause the ECU to reset the IAC:
  1. Warm the engine to full operating temps
  2. Turn engine off and then turn the key back to ON
  3. With the IAC connected, jumper pins A and B at the ALDL.
  4. Wait 30 seconds and unplug the IAC
  5. Remove the jumper at the ALDL
  6. Start the engine
  7. Adjust engine RPM to 500-550 in Drive using the throttle stop screw on the throttle body.
  8. Shut the engine off and plug the IAC back in.
  9. Restart the engine
  10. Set TPS to .40-.44 volt or whatever your chip manufacturer specifies
The above procedure should reset the IAC and get you close to final values. Then, to fine tune it, follow the procedure below:

(note that everything below should be done with the car in PARK, not DRIVE)
1. Start the car and get it up to operating temperature.
2. With the engine-off, key-on, adjust the TPS per the GNTTYPE procedure so that you get the following on the Scanmaster:
0.40 to 0.42 volts with your foot off the gas pedal.
Over 4.0 volts when you push the gas pedal to the floor.
(note: many people say you need to have at least 4.6 or more volts when you floor the gas pedal. This is not true. Just make sure it's comfortably over 4.0 volts when you floor it. 4.25 volts would be fine. You should not have to ream out the TPS slots as is sometimes suggested. Try sliding the TPS all the way forward and then rotating it to achieve the 0.42 volts - this usually helps to get the highest WOT value possible.)
3. After securing the screws that hold the TPS, start the car. Make sure that at idle, your TPS volts are BELOW 0.46 volts (I make sure mine are in the 0.42 to 0.44 range for a margin of safety). On most cars, the TPS volts jump by about 0.02 when you start the engine - i.e. if you set the TPS to 0.40 volts with the engine off, you will probably see it jump to 0.42 volts after you start the engine.
4. Once the car is warm and in closed-loop, look at your IAC reading at idle. Make sure they are in the 15 to 40 range, with 20 to 25 being"perfect".
If the IAC reading is too LOW, then turn the throttle body screw a little counter-clockwise (i.e. CLOSE the throttle plate a little more).
If the IAC reading is too HIGH, then turn the throttle body screw a little clockwise (i.e. OPEN the throttle plate a little more).
(Warning: if the TPS volts go over 0.45 volts while turning the throttle body screw clockwise, you are no longer in idle mode. Shut the car off and go back to Step 2.)
5. Repeat Steps 2 through 4 above until you get the TPS and IAC readings to be in good values:
TPS at 0.40 to 0.42 volts with the engine-off, key-on.
TPS reading over 4.0 volts when you floor the gas pedal with the engine-off, key-on.
IAC reading between 15 and 40 with the car running at idle, engine warm, in closed loop.

It's an iterative process and takes a little time, but once you get there, you should have a good idle and minimize the chance of tip-in stumble. As others have mentioned, biasing the IAC to the low-end of the acceptable range might help improve your tip-in problem.

One other thing to keep in mind - the exact IAC steps required to idle the car changes every day. If the incoming air is hot, it will open more to maintain idle speed (higher counts). If the incoming air is cold, it will open less (lower counts). So, if you set your TPS and IAC on a warm day, don't be surprised if the IAC steps are lower on a cold day, and vice versa. This is OK as long as they are generally in the ranges shown above.

The good thing about the above is that it costs no money to do as long as you have a ScanMaster or some other scan tool.

Good Luck"

This is what I came up with , + Please notice the second pic shows my MAF value At only 42 @ ~ 4500 RPM , in park . Tomorrow 'Ill take it out on the Parkway and see what it reads at 70 MPH ! ( Do You think I should still go thru with the Back orderd Cardone MAF from GBody ? )

Thanks for any opinions and / or advice. Without you guys , I'd be SOL !!!

Richie----Lockman
 

Attachments

  • Data Log at Idle 4-27-2019.JPG
    Data Log at Idle 4-27-2019.JPG
    93.1 KB · Views: 44
  • Low MAF Value ~ 4500 RPM in Park.JPG
    Low MAF Value ~ 4500 RPM in Park.JPG
    58 KB · Views: 46

CzyKats44

Dis-Member
Lockman, Just something else to get eyes on if you haven't remedied this issue yet...

I had an intermittent situation thats sounded eerily similar to what you described in post #1. About 60% of the time, initial light accel and cruse in the 1700-2300 rpm range it would buck a little. It took me a while to hammer down the exact range and conditions this was happening, being hampered by its intermittent nature. Under load - no problem, if i pushed the pedal past the buck - no problem, if it shifted and rpms dropped - no problem. I disconnected the TCC plug to isolate that, problem persisted. Must have reset the TV about three times. I swapped out some spare IAC and TPS sensors I have and set them by the book. Swapped out a MAF with one I have that I know worked well before - no dice. I shook down the cam sensor and crank sensor wiring - rock solid at idle. I ultimately read about similar symptoms on another forum and I went to check the Cam Sensor cap screws and BAM! - the whole shaft/cap assy twisted in the bore.

Apparently, right at that rpm range the centrifugal force rotated the cam sensor shaft housing (and attached cap) just barely enough to affect timing but not stall the engine.

Check the torque of the cam sensor shaft assy mounting clamp and bolt.
 

Lockman

OH, OK .......Now I get it
Thanks , Brother . I will Look into that this weekend. Question : If it is loose , Then the timing would be thrown off , under load , and cause it th run a bit ' Off " ? .. Makes sense , the way you explained it. I have never checked the mounting clamp and bolt since I 've owned it. I will let you know.
 

CzyKats44

Dis-Member
No Prob, happy to share if it helps someone who's chasing their tail. I just torqued mine and it corrected the issue. As for timing, seemed to run fine. I do have the little plug in tool for making sure its set properly but I've been busy and haven't gotten to it yet. But I do plan on setting it properly at some point.
 

Lockman

OH, OK .......Now I get it
Hi Greg ,
I did check that hold down bolt . it was Loose , but the cap was not ? . Thanks for pointing this out .
Lockman..... Richie
 
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