IHADAV8.com - Turbo Buick Tech, and Nonsense
Tech Area => General Buick Tech => Topic started by: Shimy87 on May 26 2021, 03:01:50 PM
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Finally got to put some miles on the kids car, about 100 miles. Most everything is good except it has a slight miss when under very light load. example when you go down hill or come up behind a car going 5 mph slower, so your still in the throttle but barely, then i can feel the miss. It goes away as soon as a load comes back on car or you give it more throttle. Have not been able to look at anything yet. Was going to start with plugs/wires but really not sure where to start??
also think the shift cable from throttle body needs adjustment, at 40-45 mph, very light throttle it hunts back and forth sometimes for what gear it wants....think I need to depress tab and pull cable back a couple clicks??
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what are the O2s doing when the car has the apparent light miss?
On the second problem, is the car shifting at the normal shift points mph-wise?
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O2's seem to be jumping all over
shifts at normal points, converter locks up normally also
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It should be in closed loop so the numbers would jump around, but, I was trying to see if it was going leaner than it normally is at the point of the light miss. Seeing more low numbers than usual.....
It does not sound like a TV cable adjustment if it is shifting at the normal mphs
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I think it is low when it happens but will double check.....I did notice when i completely lift off throttle I saw numbers less than 100 and that seemed like something I had never seen on my car
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that is too low. Check your fuel pressure. Add a little fuel to idle. Of course, our old favorite..chec k for an air leak...
You can also put it on blms and see if they jump up when you let off
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will do, BLM was at 118, on the air leak..... now that I have a vacuum gauge in this car when let off at cruise it shows 21 lbs vacuum.....doe s that tell me anything?
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Sounds healthy. Don't put a lot faith in your fp gauge. Those small cheap ones can be off 20%
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Wonder if a pcv that is not working right could let too much air back in when you let off?
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Used a good fp gauge and set it to 43 with hose off....it was actually at 49 with hose off
Pcv seems good, it rattles
Have not run with any boost yet, now that I have this fp gauge hooked up will check it at 5 then 10 lbs and make sure I get correct fp raise
Only have a bit over 100 miles put on, should I put more on before putting some boost at her
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try adding a little fuel to idle in the chip and see if that does the trick
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I have a tt chip, I don't see where I can adjust idle fueling, just WOT adjustments in different gears?
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Oops, I forgot. My tt chips (SD) give you that ability. Raise the fp 2 lbs and see if it changes. Or plug the PVC line and see if that changes it. Make sure the hoses between the mag and turbo are all well connected.
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Also, disconnect the battery memory wire and clear the ecm. Then go drive the car and let the chip relearn.
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my best guess is reset the chip :D
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Adjusted fp to 43 lbs, hose off, it was at 49. Also unplugged computer over night. Now my crusing blms are 125-128 so thats better from 118. Still has the miss and now also has a slight stumble from off idle like leaving a stop light. Lowering the fp got the computer to stop pulling fuel at cruise I think?? Any ideas? Don't think I should crank up fp beyond 49 with hose off?
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warm it up and check the compression. give it the same number of "bumps" on each cylinder and see if they all resemble one another
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Each got 7 bumps and every cylinder was right at 150 on my old casper gauge. Going to put some new ngk UR5 plugs in tomorrow to remove that potential issue. Then run it with fp gauge hooked up to see if maybe the pump is going??
The O2s jump all over but do seem to show lower low numbers than my car does, don't know what if anything that is telling me?
It runs very smooth when on the gas or up to highway speed but at that 40 mph very low throttle it has that noticeable miss
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Does not sound like a pump problem. Still sounds like it is going lean at that point
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Do all my usual suggestions :D
Be sure the intake bolts are all about the usual tightness. Spray carb cleaner around throttle body/plenum joint.
Around the vacuum block and around the base of the plenum. Be sure the joints between the maf and the turbo are not leaking. Pinch off the pcv line. Make sure none of the metal vacuum lines are cracked and check valves are good... make sure there is no small leak under the egr valve base. Spray around the IAC to make sure it is not cracked or leaking
It sounds like it is pulling too much air from some place as the throttle is cracked...
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MIght also try setting the Translator one step rich on the idle.
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Checked and zero leaks anywhere. Tps was a bit low at ,38 so corrected that. No time to test drive but will tonight. On the tps ....I can't get WOT to get above 4.35. Not causing this issue but its low
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That is not low at all. It does not matter if it is set there or 4.8. It does not use tps other than for normal cruising. .38 is also in the window of adjustment. Factory says .35 to .45v as I recall. If the car is running and you move the tps, you will get a change in idle but when you turn it off and restart it, the idle returns to where the chip is telling it to idle.
I am sure you sprayed around the injector bases so my next suggestion is to go to one step richer on the maf
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did you put a new Denso O2 sensor in it?
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No, but they are only $15 so I will put one in
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If no leaks,then o2 or maf sensor calibration would seem likely
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Hope its tha O2 sensor, just tested car and it still does it. Tried maf setting at standard and at 10 % rich at idle....the miss feels the same in both but the readings are lower in standard setting.
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I'm really lost. It seems like it is getting too much air and leaning out which can cause the problem you describe. You might try switching mafs between the two cars if the O2 sensor does not fix it...
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Been wracking my brain on this one and I agree it time to start swapping known good parts and see if I can correct this. As usual your right and its got to be a fuel delivery issue. If it was a miss caused by an ignition problem I would think O2's would go up as it wouldnt be burning the fuel correctly?? I'm going to check for a leak again but last time I had so much carb cleaner sprayed everywhere I was waiting for it to burst into flames..haha.
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I think the o2s go down when the fuel does not burn correctly so the net result is a lean cylinder. I may be "misrembering" tho LOL
In other words, the O2 sensor measures the oxygen left in the cylinder after combustion but it does not measure normal air...think that is what Bob Bailey explained to me...
I used to say that three was the ideal number of buicks to own for optimum swapping...
Now, I am confused and don't know...
Can you feel it miss when the car is in Park and you crack the throttle? If so, disconnect one injector at a time and see if the problem gets worse after each one is disconnected, or do you find one that stays the same?
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Can't feel the miss in park, also hosed everything down again and no leaks found...its got to be Maf or O2. Also when driving and its happening the fp gauge was rock steady so not losing pressure.
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I would think if it was a mechanical problem, the miss would get worse under a load.
The chip should have a fuel curve built into it for part throttle operation. The maf should provide air flow measurement to the ecm to control the fuel flow from what was programmed into the chip. The O2 provides feed back from it's after the fact measurement and the ecm should fine tune the fueling to get it where it wanted it to be. That is what I understand. Therefore our two variables are really just the maf and o2. Of course the fueling is also altered by the temperature sensor that goes to the ecm. If the ecm temp reading is close to what the temp gauge reads from the water temp sender, then all should be good.
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Got the new O2 sensor in, still kinda feel it. Does the air temp sensor effect fueling? It warm today at about 85 but that temp sensor reads 125 to 145. Its installed right at the air filter. Water temp on the gauge matches the SM reading
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The factory chip only paid attention to it at cold temperatures. I believe Eric's chip use it more to affect fueling. Hotter readings would tend to pull fuel out for a leaner mix. I think I would replace it as it is cheap. Or it used to be anyway...
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swap them and see
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I just ordered one, $14, and while I'm at it going to relocate the charcoal canister and pipe the air filter down in that area. Cut the plastic "floor" out there to give it the coolest air possible
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125 to 145 is not particularly hot for under hood air if the engine has been running long enough to warm up the air under the hood......
but if the air was a lot cooler than that,then it might be enough to lean it out....
The key seems to be that the O2s look lower on the car than they do on your own car.... cheap sensors are not killers to try...
Usually air leaks and such show up on the blms but really don't make the car act up in my experience, unless they are before the throttle body. this one is really strange.
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I never did check to see if intercooler had a leak???
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It's common on an old one...be a good idea to check
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It's common on an old one...be a good idea to check
Very interesting, would also cause the increase of BLM as a vacuum leak?
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It can. It's unmetered air that was not measured by the maf. Therefore the ecm does not give enough fuel. Then the o2 screams at the ecm to add more fuel in and the blms go up
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I don't think I have any leaks with the intercooler since many years ago I did removed it to be clean, but I ever did check for any air leak. Since now I'm waiting next week for the delivery of the heater hoses, and the water hose the feeds the Throttle body. Both hoses are original, and although their look good on the outside I don't know how their look inside; Better safe than sorry.
So now I will remove the intercooler, and check for any air leaks and clean it again. Hopefully by the end of next week I will assemble all, check air leaks in the engine, and finally start and hope to see the BLM running normal or around 128.
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Found 3 leaks in intercooler. Ordered a slic for mine and will swap my stock one into kids car.
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When opportunity knocks, ... :D
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Got it switched in, finished the "cold air" induction and test drove....suces s!! No miss, runs very smooth and intake air temp runs about 10 degrees above actual air temp so happy with that.
Prior owner put new springs in front but still had old in rear so it sat dragging its ass. We put some new ones in back and its got a nice stance back, about 1/2 inch taller in rear now than front.
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A little rake looks good on these cars. Glad you got it sorted out. Some times troubleshootin g is like trying to find your way thru a maze.