Buick 3800 difficulty in restarting/cranking hot engine.

[Carlostrece]

My 97 Buick Park Ave (106K miles) always starts and runs great on 89 octane gas.

With 87 octane the starter has difficulty cranking the engine when hot. Sometimes it won't restart on hot summer days. But then after 15 min cooling down with hood open, it starts right up.

Specifically if it's been driven, briefly parked, then try to restart, it has difficulty cranking over the engine (if using 87 octane). Summer before last, my certified mechanic checked my battery, starter, and crank position sensor. Those things are working fine.

His theory and mine is that there might be some carbon buildup in combustion chamber that's increasing compression.

The engine only has the issue when using 87 octane gas. It has no problem using 89 octane gas.

I've always used top tier fuel while I've owned the car from 50-106K miles. The 1st owner likely used cheap (non top tier) gas from 0-50K miles.

The car has had the hot restart difficulty with 87 octane gas since I bought the car. I've always worked around it by using 89, but the car is supposed to be able to use 87.

Do you think it might be carbon buildup on pistons or something else? I'd appreciate advice. Which fuel system cleaner additive is safe and effective? Yamalube or something else?

 

[Cressida]

Have you checked to make sure you have spark when it's turning over but not starting? I would check for spark by pulling one of the plug wires at the top of a coil pack.

 

[14Accent]

Do you still have the engine beauty/sound cover installed? If so, remove it and repeat the experiment. Does it still start hard with the engine cover removed? If not, vapor lock is a very likely cause of your hard starting.

 

[FZ1]

My 97 Buick Park Ave (106K miles) always starts and runs great on 89 octane gas.

With 87 octane the starter has difficulty cranking the engine when hot. Sometimes it won't restart on hot summer days. But then after 15 min cooling down with hood open, it starts right up.

Specifically if it's been driven, briefly parked, then try to restart, it has difficulty cranking over the engine (if using 87 octane). Summer before last, my certified mechanic checked my battery, starter, and crank position sensor. Those things are working fine.

His theory and mine is that there might be some carbon buildup in combustion chamber that's increasing compression.

The engine only has the issue when using 87 octane gas. It has no problem using 89 octane gas.

I've always used top tier fuel while I've owned the car from 50-106K miles. The 1st owner likely used cheap (non top tier) gas from 0-50K miles.

The car has had the hot restart difficulty with 87 octane gas since I bought the car. I've always worked around it by using 89, but the car is supposed to be able to use 87.

Do you think it might be carbon buildup on pistons or something else? I'd appreciate advice. Which fuel system cleaner additive is safe and effective? Yamalube or something else?

Check the condition of the battery.

 

[Carlostrece]

Check the condition of the battery.

The battery and starter are newish and in perfect condition. The crank position sensor is functioning properly too.

 

[FZ1]

The battery and starter are newish and in perfect condition. The crank position sensor is functioning properly too.

Good. Was hoping for an easy fix 4 you.

 

[Carlostrece]

Good. Was hoping for an easy fix 4 you.

OK. So what's the fix? To date all I have is a theory that the problem might be carbon buildup in combustion chamber, but no confirmed diagnosis.

So far my easy fix has been using 89 octane (mid grade) gas. That's an easy, effective bandaid; but I'd still like to fix the underlying problem, if possible.

 

[Chris142]

If there was carbon adding compression I don't see how a different octane would make any difference as it's not squirting fuel until after a couple of revolutions.

Plus you would need a lot of carbon to raise the compression that much to effect it.

Usually this is caused by...

1. Heat soaked starter
2. Dirty cables.
3. Undersized cables.
4. Weak battery or not enough battery capacity.

How did a mechanic "Test" the starter?

 

[SammyChevelleTypeS3]

My 1976 Chevelle with 400 cui 4 barrel carb engine with 52,000 mi did the same exact thing. I started using 89 to 93 pure gas and it never did it while using those. No mechanic could solve for me either. It has nothing to do with the starter or battery etc... it is a FUEL or engine tune/timing issue straight up. On an engine that starts and runs fine on certain gas can not be an issue with the starter or battery since it runs fine with high octane fuel. This is the only thing I could find on web:

Chevy​

The hard starting issue with a Chevy 400 when using low octane gas can be attributed to several factors. The fuel quality is crucial, as low octane gas can lead to poor combustion and insufficient fuel pressure, resulting in hard starting problems.
Additionally, air pockets in the fuel system can cause intermittent starting issues, especially after jostling the vehicle or improper bleeding during maintenance. Battery and alternator issues can also contribute to hard starting, as they may not provide enough power to start the engine. It's important to address these issues promptly to ensure smooth engine operation.

carcaresite.com

 

[Carlostrece]

If there was carbon adding compression I don't see how a different octane would make any difference as it's not squirting fuel until after a couple of revolutions.

Plus you would need a lot of carbon to raise the compression that much to effect it.

Usually this is caused by...

1. Heat soaked starter
2. Dirty cables.
3. Undersized cables.
4. Weak battery or not enough battery capacity.

How did a mechanic "Test" the starter?

I don't know, but the starter is only a few years old with less than 6K miles on it. He still tested it anyway, but I don't know how.

The battery is only 1 year old and is the highest capacity flooded G34 I could get.

The octane used makes a huge difference in summer when retarting after driving.

 

[Trav]

You may have a weak ICM (ignition control Module) as the age they weaken from heat, the cast iron bracket is not much of a heat sink.
this is a well known issue. SMP makes one that works well. If you do end up changing it clean the bracket spotless and apply some heat sink compound to it before bolting on the new module, check the coils for cracks. Don't load the parts cannon get it checked out carefully.

https://www.amazon.com/ARCTIC-ACTCP...=heatsink+compound&qid=1762735786&sr=8-8&th=1

https://www.rockauto.com/en/moreinfo.php?pk=49809&cc=1019876&pt=7172&jsn=485

 

[Carlostrece]

My 1976 Chevelle with 400 cui 4 barrel carb engine with 52,000 mi did the same exact thing. I started using 89 to 93 pure gas and it never did it while using those. No mechanic could solve for me either. It has nothing to do with the starter or battery etc... it is a FUEL or engine tune/timing issue straight up. On an engine that starts and runs fine on certain gas can not be an issue with the starter or battery since it runs fine with high octane fuel. This is the only thing I could find on web:

Chevy​

The hard starting issue with a Chevy 400 when using low octane gas can be attributed to several factors. The fuel quality is crucial, as low octane gas can lead to poor combustion and insufficient fuel pressure, resulting in hard starting problems.
Additionally, air pockets in the fuel system can cause intermittent starting issues, especially after jostling the vehicle or improper bleeding during maintenance. Battery and alternator issues can also contribute to hard starting, as they may not provide enough power to start the engine. It's important to address these issues promptly to ensure smooth engine operation.
carcaresite.com

That sounds like my issue. Thankfully 89 octane top tier gas works fine. 87 top tier does not work well in summer. This is only a hot summer issue.

In fall, spring, and especially winter, I can use 87 octane with no problems.

 

[Carlostrece]

You may have a weak ICM (ignition control Module) as the age they weaken from heat, the cast iron bracket is not much of a heat sink.
this is a well known issue. SMP makes one that works well. If you do end up changing it clean the bracket spotless and apply some heat sink compound to it before bolting on the new module, check the coils for cracks. Don't load the parts cannon get it checked out carefully.

https://www.amazon.com/ARCTIC-ACTCP00080A-MX-6-4-g/dp/B09VDL3CW6/ref=sr_1_8?dib=eyJ2IjoiMSJ9.-iE9eo-Uh2IpzBCByfgPrOSfFZaxC5BKUo1ZZCIxeNQqouTl_o8o408B5JkfSeToVKiP5DAzIY3rdGSjKSFrUgmgjarDwz5T0SieaRMQF17DYzF3XbXqajTzBUEw2leLpQKqaTB5OQcKZzfd15eI8pweUDL3DLDNIIO1crlX9mHwXzK0MtoHSlJ6ckAz1cEROzR3DLQF4hekIIlfOWmb9OVHbA42cuA-81STgx8pW8Q.wuqX9WDE6yimBO7wa1ylNNWFHTJnFXeo5Z_-pdZjaUE&dib_tag=se&keywords=heatsink+compound&qid=1762735786&sr=8-8&th=1

https://www.rockauto.com/en/moreinfo.php?pk=49809&cc=1019876&pt=7172&jsn=485

I will keep that in mind. The prices are amazingly reasonable. Thanks!

 

[FZ1]

That sounds like my issue. Thankfully 89 octane top tier gas works fine. 87 top tier does not work well in summer. This is only a hot summer issue.

In fall, spring, and especially winter, I can use 87 octane with no problems.

So, that's all it is. Gas blends change in Summer and Winter and your car don't like the summer blend 87.

 

[Carlostrece]

So, that's all it is. Gas blends change in Summer and Winter and your car don't like the summer blend 87.

It absolutely doesn't like summer 87 octane gas, but why? Is it a problem with car or gas?

 

[Lubener]

Electrical resistance increases with temperature. I would remove and clean all B+ and ground connections.

I don't think it has anything to do with the octane and cranking ability of the starter.

 

[97prizm]

My 97 Buick Park Ave (106K miles) always starts and runs great on 89 octane gas.

With 87 octane the starter has difficulty cranking the engine when hot. Sometimes it won't restart on hot summer days. But then after 15 min cooling down with hood open, it starts right up.

Specifically if it's been driven, briefly parked, then try to restart, it has difficulty cranking over the engine (if using 87 octane). Summer before last, my certified mechanic checked my battery, starter, and crank position sensor. Those things are working fine.

His theory and mine is that there might be some carbon buildup in combustion chamber that's increasing compression.

The engine only has the issue when using 87 octane gas. It has no problem using 89 octane gas.

I've always used top tier fuel while I've owned the car from 50-106K miles. The 1st owner likely used cheap (non top tier) gas from 0-50K miles.

The car has had the hot restart difficulty with 87 octane gas since I bought the car. I've always worked around it by using 89, but the car is supposed to be able to use 87.

Do you think it might be carbon buildup on pistons or something else? I'd appreciate advice. Which fuel system cleaner additive is safe and effective? Yamalube or something else?

Charcoal canister maybe? Does it smell like gas on lower octane?

 

[Carlostrece]

Charcoal canister maybe? Does it smell like gas on lower octane?

I haven't noticed any gas smells.

 

[SOUNDMAN5000]

My mother had a 94 Buick with the 3800, its been so long ago I can't remember exactly what it was doing but was not running right and her normal mechanic we had used for years could not figure out what was wrong. I took it to a friend and he gave one listen and said replace the Throttle Position Sensor ( a $80 part and super EZ to replace ) I changed it out in 5 min and fixed the issue.
as far as the gas, I have no idea but I wonder could it be the Ethanol in our gas as 90's engines don't always like Ethanol?
Why not try a Top rated PEA based fuel cleaner to address carbon? Have you changed the fuel filter? Being Ethanol perhaps it just needs the 89+ octane being a older 90's engine? Gas sure ain't what it was in the 90"s Change brand of gas perhaps or the station you buy your gas.

 

[SammyChevelleTypeS3]

My mother had a 94 Buick with the 3800, its been so long ago I can't remember exactly what it was doing but was not running right and her normal mechanic we had used for years could not figure out what was wrong. I took it to a friend and he gave one listen and said replace the Throttle Position Sensor ( a $80 part and super EZ to replace ) I changed it out in 5 min and fixed the issue.
as far as the gas, I have no idea but I wonder could it be the Ethanol in our gas as 90's engines don't always like Ethanol?
Why not try a Top rated PEA based fuel cleaner to address carbon? Have you changed the fuel filter? Being Ethanol perhaps it just needs the 89+ octane being a older 90's engine? Gas sure ain't what it was in the 90"s Change brand of gas perhaps or the station you buy your gas.

The ethanol in the gas could be part of the problem. Many classic cars had fits and troubles due to ethanol use. The carbs and the fuel lines swelling and clogging up. Today there are kits to use to update fuel lines as well as gaskets etc to swap out on certain carbs. I had swapped totally to 93 octane pure gasoline with my last Chevelle to avoid the ethanol issue and it worked out for me. Ethanol is no longer an issue with any newer vehicles.