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Discussion Starter #1
My LT1 is suddenly running awful after getting my AC recharged. I also just cleaned and oiled my air filter, and did the oil filter adapter seals but even with the ac off it still runs like garbage so im ruling the AC out. The adapter seals also makes no sense to cause a mis. I did spray all around the engine with brake cleaner last night to clean up the mess I made with AC compressor oil/dye. Maybe I ruined something by doing this? It was mostly on the passenger side though and the driver side its where the misfire is.

Here are some videos of the idle:
https://youtu.be/gjPnAf16ad0
https://youtu.be/IBtzNt5NF70

Seems to only be on the driver side. Exhaust sputters and is not smooth. The exhaust is also dark and smokey on driver side. Strangely if I unplug one of the driver side spark plug wires I don't notice any change in idle. I tried all 4 on the driver side with the same result for each one, no noticeable change in idle.

Today on the way to get my AC system charged it seemed to run fine. It wasnt until about halfway home that it started to act up. Im hoping its the oxygen sensor connection since I had an issue with this after the filter adapter swap. Also the knock sensor wiring somehow became stripped, so hopefully it's just shorting on something? I noticed this after I removed that metallic like tape during the oil filter adapter gasket swap since it was all about peeled off anyways and totally soaked in oil.

The check engine light is off for now.

At idle the driver side exhaust has a periodic (but not on a perfect cycle) sputter as seen in the videos. Under throttle in park it sounds normalish. Under heavy throttle in gear it nearly bogs out and has awful acceleration and sounds terrible. Under light throttle its a total dog, sputters pretty bad, and bogs and I can feel some surging.

Before I did the AC, oil filter adapter, and air filter, I recently (<500 miles) replaced the opti, I was getting code 36 and 42, which vanished after the opti swap. I used a cheapo amazon unit with 3 year warranty. Maybe it's dieing? It is super hot (nearly 100 F) today. I installed an MSD cap and rotor and applied RTV to all the seams and blue locktite to everything. I also did the opti and water pump seals in the timing cover, water pump, plugs, and wires at the same time. I used 10.5mm Busidin silicone wires off amazon and double platinum bosch plugs. It was running great after these repairs/swaps.

Any ideas?

Thanks, Mark
 

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Hi, sorry to hear all the trouble with your maintenancce work.
If you search you will see for some reason these LT1's don't like Bosh stuff too much, like plugs and O2 sensors. So you are rolling the dice there.

Also the B-body MAF is sensitive and oiling the air filter is tricky as when you suck in air some oil can get on MAF and make it very unhappy. Rolling the dice again unless you are aware of this and were not generous with the oil.

Keep in mind PCM sees 2 4bangers and not one V8 so that may help you track down the issue. May want to check PCM for codes as not all will turn the CEL on.

When you pulled each plug wire on DR side while car running you saw spark on the end ?

I'll go check the vids now.
-ALF out...
 

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There is a a chance your fresh air filter oil has contaminated the MAF. Remove the filter, clean the sensor in the MAF. Don't touch it, use the correct CRC spray. No brake cleaner! Once clean, reinstall, make sure facing the right way, and start it without the filter. See if there is an improvement.
 

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Boy, did you and this OP both go out recently and kick a puppy? lol

https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1316970-car-cranks-but-wont-start.html
You both got dam near identical grief right now, even down to the aforementioned likely infamous "too much filter oil got on the MAF" thing. I hope Head- sees this to make sure his is cleaned and the sensor is installed in the correct direction. Regrettably all too often I've found the work I just done did is the (at least round-about) cause of a current gremlin.



This is especially not limited to work you've done. The part about "...suddenly running awful after getting my AC recharged." Cause, correlation or coincidence. :: squinty eyes ::
 

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There is a a chance your fresh air filter oil has contaminated the MAF. Remove the filter, clean the sensor in the MAF. Don't touch it, use the correct CRC spray. No brake cleaner! Once clean, reinstall, make sure facing the right way, and start it without the filter. See if there is an improvement.
On Amazon I see the red can and silver can (more than 3x the cost). Which one are you supposed to use for LT1?
 

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Red = $4, silver = $7. I never heard of silver before and just use red. The point is steer away from old school 'carb cleaner', brake cleaner, Spray 9, engine greaser or anything else.
 

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Discussion Starter #7
Hi, sorry to hear all the trouble with your maintenancce work.
If you search you will see for some reason these LT1's don't like Bosh stuff too much, like plugs and O2 sensors. So you are rolling the dice there.

Also the B-body MAF is sensitive and oiling the air filter is tricky as when you suck in air some oil can get on MAF and make it very unhappy. Rolling the dice again unless you are aware of this and were not generous with the oil.

Keep in mind PCM sees 2 4bangers and not one V8 so that may help you track down the issue. May want to check PCM for codes as not all will turn the CEL on.

When you pulled each plug wire on DR side while car running you saw spark on the end ?

I'll go check the vids now.
-ALF out...
Thank you for the reply!

Perhaps its the bosch plugs. Doesn't seem to be one cylinder though but maybe it is. I also didn't pull them while the engine was running and it was very sunny so I couldn't see any sparks.

I was rather generous with the air filter oil but wouldn't a dirty MAF sensor cause all the cylinders to miss, not just the driver side?

I bought a cheap $20 code reader on amazon but i either have no codes or it doesn't work. The CEL light does not flash but the fans do come on when i plug in the device and turn the key on (not stating the engine). The ABS feature did seem to work and code 12 was coming up but lets not worry about that for now. This is the reader I used but will be returning it.
INNOVA 3123 GM OBD1 Code Reader https://www.amazon.com/dp/B000EVU8C0/ref=cm_sw_r_cp_apa_i_8aqtDbXWSFKQG

There is a a chance your fresh air filter oil has contaminated the MAF. Remove the filter, clean the sensor in the MAF. Don't touch it, use the correct CRC spray. No brake cleaner! Once clean, reinstall, make sure facing the right way, and start it without the filter. See if there is an improvement.
Thanks for the reply!

When i got the car the MAF sensor doohickeys were all totally covered in dirt or something. I cleaned them with a brush and it seemed to make no difference as the car was running fine before despite the dirt. I will get correct spray and try cleaning it but i dont see how only the driver side would be affected by a dirty MAF sensor.

Boy, did you and this OP both go out recently and kick a puppy? lol

https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1316970-car-cranks-but-wont-start.html
You both got dam near identical grief right now, even down to the aforementioned likely infamous "too much filter oil got on the MAF" thing. I hope Head- sees this to make sure his is cleaned and the sensor is installed in the correct direction. Regrettably all too often I've found the work I just done did is the (at least round-about) cause of a current gremlin.

This is especially not limited to work you've done. The part about "...suddenly running awful after getting my AC recharged." Cause, correlation or coincidence. :: squinty eyes ::
Thank you for this thread! Some how I didn't find this in my search. Seems i cant get the forum search to work well for me but google did return some useful results. Unfortunately it doesn't seem he ever figured out the solution 😕 and so far my car has not failed to start since this issue arose.

As for cause, correlation, or conicidence. Seems like conicidence to me except maybe I fried something with the brake cleaner, the O2 sensor is not connected properly, or the knock sensor wire being nearly bare is causing an issue. Could be the MAF or plugs but I suspect the MAF sensor would cause both banks to mis, and the plugs are supposed to be good plugs but this doesn't mean anything, just my intuition. My headers make pulling the plugs a bitch for cylniders 5-8 so I hope its not these ones lol
 

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Hi, AFA testing your code reader it is easy enough to unplug the sensor on the Water pump, or the MAF and start the car. That should make CEL go on and you can use reader to get the codes. Then turn car off, plug stuff in, start car and use reader to clear codes and turn CEL off.

That should give you a baseline with the reader working or not.
the reviews on that reader leave a lot to be desired, but if the pins are not sliding into the plastic case you may have a good one. Good Luck.

You can also use a DVM to test resistance on your new wires to be sure they are not defective to rule them out as a problem.

-ALF out...
 

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Hi, AFA testing your code reader it is easy enough to unplug the sensor on the Water pump, or the MAF and start the car. That should make CEL go on and you can use reader to get the codes. Then turn car off, plug stuff in, start car and use reader to clear codes and turn CEL off.

That should give you a baseline with the reader working or not.
the reviews on that reader leave a lot to be desired, but if the pins are not sliding into the plastic case you may have a good one. Good Luck.

You can also use a DVM to test resistance on your new wires to be sure they are not defective to rule them out as a problem.

-ALF out...
Thanks for the suggestions!

I started the car with the temp sensor unplugged. CEL came on. Shut car off, plugged in code reader, turned car on (manual says to not run the engine to read codes), no codes so I guess it doesn't work... the reader is essentially a selectable jumper that shorts the proper pins to check engine or abs codes by flashing the respective light on the dash. I didn't realize it was this style until I bought it but I read that jumpers dont work to read codes on these cars.

Before installing the new wires I tested them all and they were about 400 ohms if I can remember correctly.

Anyways the car is running fine now. I cleaned the MAF with electrical contact spray. No noticeable grime or oil was on it or came off during spraying. I also disconnected the DS O2 sensor and sprayed the contacts and reconnected it. I also zip tied the O2 sensor cables to the oil cooler lines to keep them away from the header and I separated the wires near the connector as they are also missing missing insulation near the connector and were too close for comfort. Not sure if any of this helped or not. The day the issue started I also added a can of gumout with PEA (in the can like seafoam comes in) to the gas tank. Maybe my injectors are clogging and the gumout is cleaning them? Idk but the car just ran great for about 15 minutes or so.
 

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Discussion Starter #10
Well my gremlin is back. Went for a longer drive last night and it started to run really bad after about 20 min.

Still only on the driver side. Seems to happen only when fully warmed. which makes me think it's a bad opti. I read that the cheap sensors can fail at high temp. But I'm not sure why it would only effect the driver side

CEL came on briefly but the engine started to run good for about 2 second and then the light went off and it was missing again.

According to this thread:

https://ls1tech.com/forums/lt1-lt4-modifications/1649402-lt1-guru-needed-misfire-when-warm.html

it seems like it's not the O2 sensor since mine still runs bad at WOT and the issue doesn't start as soon as it goes into closed loop.

I'm totally perplexed. Gonna have to get a real scanner I suppose. Can anyone recommend a good one that's not super expensive? Preferably one that will do OBD 1 and 2.
 

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What year is your car? A good scanner may be as easy as a $10 cable and a download for scanning and programming or a $30 cable for scanning and a $300 cable for programming.


-Brian
 

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What year is your car? A good scanner may be as easy as a $10 cable and a download for scanning and programming or a $30 cable for scanning and a $300 cable for programming.


-Brian
Sorry I forgot to mention its a 1994, OBD1. Today the car was mostly running good. CEL did the same thing today as last night, but this time it ran good longer after the light went off.

$300 just for a cable? Seems ridiculous, is it made from gold?
 

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Never ever you those plugs, Bosch platinum plugs are known for going bad i would definitely say that's your issue and if you want some good advice stay with O.E. parts if you can. I now buy all my o.e. parts from these two websites mostly because their real parts and much cheaper then the dealers and they have Discontinued parts that gm dealers can't order anymore.
check these links out,

https://www.gmpartsprime.com/oem/gm-spark_plug-19301813.html?Make=Chevrolet&Model=Impala&Year=1996&Submodel=&Filter=()

https://www.gmpartsgiant.com/parts-list/1996-chevrolet-impala/engine-assembly-cylinder-head-related-parts.html?PNC=4c3a3e337c2a89a2729bede51e1649ff

Almost the same price but 6 bucks each. better than the dealer's 11 bucks

Best of luck but get those plugs out regardless.
 

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Had a very similar issue with my 96 although that's OBDII and the scanner showed which cylinder was misfiring. You would notice it once it warmed up. Ended up being one plug wire with the plug heat shield contributing. Even after swapping the one plug wire the misfire would continue with the heat shield on. I replaced the heat shield with spark plug insulation boots (or whatever they are called) and that solved it.

This all occurred after I changed the plugs and wires with AC delco parts... one bad wire/plug shield.

At first I thought it was the ICM since it seemed most noticeable after it warmed up and you were stopped (slight rumble)

Not sure what OBDI supports with respect to misfires but thought I would post my experience for you.
 

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Discussion Starter #17
There is a whole section on pcm programming, the sticky should tell you how to check things out for as cheap as possible.
Good Luck.

https://www.impalassforum.com/vBulletin/35-pcm-programming-engine-management/1281346-$eehack-94-95-lt1-tuning-flashing-datalogging-cheap.html


-ALF out...
This is wonderful! Except in struggling to find the "$4 cable" all the ones I'm seeing are around $100. Probably worth it but I'm shopping around. Still need to read that whole thread too it's quite long but is excellent so far. Thank you!

I've mentioned this before, but the old Snap-On MT2500's can be had for $100-$200 with troubleshooters which walk you through some pretty detailed troubleshooting steps and do much more than just read a code. They even had a graphing one for a while, though those might be just a bit more $$.

https://www.google.com/search?q=Snap+On+MT2500&oq=Snap+On+MT2500&aqs=chrome..69i57j0l5.5317j0j7&sourceid=chrome&ie=UTF-8
This sounds like a good option although I'm leaning towards the option Alf pointed to. I will need to learn tuning anyways and that seems like a great option but I like the idea of troubleshooting steps laid out for me too.

Never ever you those plugs, Bosch platinum plugs are known for going bad i would definitely say that's your issue and if you want some good advice stay with O.E. parts if you can. I now buy all my o.e. parts from these two websites mostly because their real parts and much cheaper then the dealers and they have Discontinued parts that gm dealers can't order anymore.
check these links out,

https://www.gmpartsprime.com/oem/gm-spark_plug-19301813.html?Make=Chevrolet&Model=Impala&Year=1996&Submodel=&Filter=()

https://www.gmpartsgiant.com/parts-list/1996-chevrolet-impala/engine-assembly-cylinder-head-related-parts.html?PNC=4c3a3e337c2a89a2729bede51e1649ff

Almost the same price but 6 bucks each. better than the dealer's 11 bucks

Best of luck but get those plugs out regardless.
Wouldn't this affect the engine at all temps if it were the plugs? Also it seems to be a multicylinder misfire on the driver side bank, based on my test I did with disconnecting the plug wires. Hard to believe 4 plugs would go bad at once. Also been running then for about 500 miles with no issues previously. I haven't had the issue in the past two days I've driven it. Today I've been driving around quite a bit without a misfire so far.

Had a very similar issue with my 96 although that's OBDII and the scanner showed which cylinder was misfiring. You would notice it once it warmed up. Ended up being one plug wire with the plug heat shield contributing. Even after swapping the one plug wire the misfire would continue with the heat shield on. I replaced the heat shield with spark plug insulation boots (or whatever they are called) and that solved it.

This all occurred after I changed the plugs and wires with AC delco parts... one bad wire/plug shield.

At first I thought it was the ICM since it seemed most noticeable after it warmed up and you were stopped (slight rumble)

Not sure what OBDI supports with respect to misfires but thought I would post my experience for you.
I did the ICM mod a while ago to pull it away from the head so I dont think it's my ICM either. So far it's been running well for the past few days without any misfires.

I think it was residual oil from my air filter at this point. Why it only effected the driver side bank is beyond me though.

Thank you everyone for a your input and help! I will report back if the misfires start up again but so far it's been running well the past few times I've driven it.
 

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Discussion Starter #18
Just wanted to follow up and let everyone know that a few hundred miles later the car is still fine. So apparently too much air filter oil seems to be able to cause misfires isolated to one bank, strange but that's what the data says.

My other thought, and justification to be conservative with air filter oil is that excess oil can get into the opti from the vacuum line on the intake. For this reason i am going to add a separate filter for the opti and plug the hole in the intake. Still wired to cause a miss on just one back but I guess its possible?

Anyways this is my experience so far
 

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If using oiled filter and you clean & re-oil it...let it sit for a day so the fluid absorbs into the filter AND oil it VERY sparingly. To much oil and it gets sucked onto MAF wires causing all kinds of drivability issues

Have had K&N filters for decades on a few cars, including the SS, without issue.

With that said cleaning MAF, carefully, for maintenance regardless of what filter is used is SOP.
 
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