Extreme misfire and then won't start

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Buick Ownership
94,96 Roadmaster, 69 Wildcat, 95 lesabre , 97 park avenue
Afternoon everybody. I own a 1994 Road Master Sedan Limited. A recent problem has arisen and it sucks a lot. When trying to start the car initially it would just crank and nothing happened. I changed the spark plugs which are 0.06'' Bosch platinum(although this is what came up when I went to the auto parts store) and not 0.05'' like it suggests, along with a new fuel filter. This seemed to fix the issue for about 10 minutes and then while still at idle it began to chug and misfire very badly and then after about half a minute just quit ALSO it smelled HOT. I asked a local auto parts person that I trust and he said that it sounded like a timing issue. I added some iso-heet and let it sit for a couple days and the same exact thing happened all over again. I am completely lost and could definitely use any help!!!!:biggun:
 

Dirtybob

Junior Member
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Buick Ownership
95 RMS
Is the car giving any trouble codes?
Tach in the Climate Control & Trouble Codes. - Chevy Impala SS Forum

Wouldn't hurt to test the coil
http://shbox.com/1/coil_testing.jpg

Also look at the ICM and Opti as well
4th Gen LT1 F-body Tech Articles

My car just started to randomly misfire too with one time where it didn't want to start. Couldn't get it to repeat, no codes stored, nothing odd looking on the data logger. All the tests above were within spec.
Decided to pull the opti and have a look inside, found the bearing on my water pump is thrashed but not leaking any (wtf?).
Opti looked clean and dry inside but the screws that hold down the rotor/optical disc were loose with no loctite. Number 1 terminal was a bit corroded but otherwise the cap & rotor looked good.
Currently waiting on parts...
 
26
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1
Buick Ownership
94,96 Roadmaster, 69 Wildcat, 95 lesabre , 97 park avenue
I see. Would that be the case even after running well for about 10 minutes both times?
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LARRY70GS

Full Member
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Oakland Gardens, N.Y.
Buick Ownership
98 Riviera, 70 GS455 Stg1
Try unplugging the mass air flow sensor. Then start the engine and let it idle. See if it will continue to run like that. If so, you can drive the car like that, it will light the CEL because it isn't seeing the MAF. The engine won't run it's best, but the car will be drive able. You can try cleaning the MAF, but you'll probably end up replacing it.

The MAF tells the PCM how much air is entering the engine, and the PCM uses that to calculate injector pulse. When they go bad or get dirty, they give a false signal to the PCM that there is a lot of air entering the engine. The PCM ramps up the fuel injection, and then the O2 sensor says it is running rich, so it pulls fuel. Back and forth like that and the engine won't run. It starts, but won't run. Typically, the engine will start cold because it is open loop. Once the computer get's looped in, the engine goes spaz and quits.

Easy check, doesn't cost anything, unplug the electrical connection to the MAF.
 

Dirtybob

Junior Member
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95 RMS
IIRC on the 8051 pcm it will default to speed density mode if the maf fails, car should still run either way.
I would add fuel pressure to the list of things to check.
 

LARRY70GS

Full Member
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Oakland Gardens, N.Y.
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98 Riviera, 70 GS455 Stg1
IIRC on the 8051 pcm it will default to speed density mode if the maf fails, car should still run either way.
I would add fuel pressure to the list of things to check.
What if the MAF is giving an incorrect signal though? Unplugging it will do what you suggest. When my MAF went, the engine went really rich and would not run in closed loop. The long and short term fuel trims went extremely negative (rich)
 

Zeroboostbuick

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2018 Regal Sportback - 2010 Yamaha R6 (track bike) Past cars: 92 LeSabre, 98 Regal, 02 GrandPrixGT
When the MAF Fails, the car might stall when idling, but at part throttle it will chug along.

When there is a MAF malfunction, the car will bypass the MAF and run of off the Volumetric Efficiency/Coefficients table(s) in closed loop fueling.

Some Cars reference the VE table(s) at all times while other cars only use the VE table(s) when the MAF fails or malfunctions.

IF your car will stay running with a little throttle but dies when you let of the throttle (while parked), it might be MAF related.

Problem with the VE table(s) is they might be very much off from optimal fueling unless they been tuned.
So Running the car with out MAF might be VERY hard on sparkplugs and will foul them to death sooner or later.
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LARRY70GS

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Oakland Gardens, N.Y.
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98 Riviera, 70 GS455 Stg1
My MAF did not fail, as in no signal. My car was undriveable until I pulled the electrical connection. Only then was I able to drive the car. Again, my MAF did not fail completely, it just sent the PCM a signal that there was more air entering the engine then there was.


When there is a MAF malfunction, the car will bypass the MAF and run of off the Volumetric Efficiency/Coefficients table(s) in closed loop fueling.
In my case, the MAF was clearly malfunctioning, but the PCM did not bypass it without me unhooking it. Again, it would not run in closed loop. This was a 98 Supercharged Riviera. Maybe later PCMs were smarter. My car would run fine when started cold, then 10 minutes of idling and it would stall.
 

Zeroboostbuick

Active member
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S.W. Ontario Canada
Buick Ownership
2018 Regal Sportback - 2010 Yamaha R6 (track bike) Past cars: 92 LeSabre, 98 Regal, 02 GrandPrixGT
My MAF did not fail, as in no signal. My car was undriveable until I pulled the electrical connection. Only then was I able to drive the car. Again, my MAF did not fail completely, it just sent the PCM a signal that there was more air entering the engine then there was.




In my case, the MAF was clearly malfunctioning, but the PCM did not bypass it without me unhooking it. Again, it would not run in closed loop. This was a 98 Supercharged Riviera. Maybe later PCMs were smarter. My car would run fine when started cold, then 10 minutes of idling and it would stall.
You are correct... Some cars work differently than others.
 
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0
1
Buick Ownership
94,96 Roadmaster, 69 Wildcat, 95 lesabre , 97 park avenue
These are all well and good suggestions and believe me I will try them out. Is there any possibility that having my spark plug gap too far open would lead to an eventual flooding of the engine. Because I shit you not both times it has ran better than ever before then after about 10 minutes it gets really chuggy and then will die. Also when it sits after dying and trying to start it, it will smell rich like it has been flooded.
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LARRY70GS

Full Member
1,884
42
48
Oakland Gardens, N.Y.
Buick Ownership
98 Riviera, 70 GS455 Stg1
These are all well and good suggestions and believe me I will try them out. Is there any possibility that having my spark plug gap too far open would lead to an eventual flooding of the engine. Because I shit you not both times it has ran better than ever before then after about 10 minutes it gets really chuggy and then will die. Also when it sits after dying and trying to start it, it will smell rich like it has been flooded.
No, plug gap would not do that. The rich smell is typical of a bad MAF. Symptoms only occur in closed loop, so it will start cold and run just fine, but warm up and go closed loop and the MAF tells the PCM there is more air entering the engine than there really is. That leads to the engine running rich then lean, then rich.

It takes 5 seconds to unplug the MAF, and then you will know if it is the culprit or not. Doing this test costs nothing.
 
26
0
1
Buick Ownership
94,96 Roadmaster, 69 Wildcat, 95 lesabre , 97 park avenue
No, plug gap would not do that. The rich smell is typical of a bad MAF. Symptoms only occur in closed loop, so it will start cold and run just fine, but warm up and go closed loop and the MAF tells the PCM there is more air entering the engine than there really is. That leads to the engine running rich then lean, then rich.

It takes 5 seconds to unplug the MAF, and then you will know if it is the culprit or not. Doing this test costs nothing.
Thank you for the advice. I will remove the spark plugs to allow excess gas to evaporate and try this tomorrow, updates are soon to follow
 

HotZ28

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1996 Roadmaster Limited Collectors Edition 58k - 1996 PAU
IF you want to clean out the cylinders from excessive raw gas, push the accelerator pedal to the floor and that will disable the fuel injectors from pouring more fuel into the combustion chambers when trying to start!. If the plugs are too wet, they may not fire, so you may have to remove them and clean/replace them. In addition, do you have any codes?
 
26
0
1
Buick Ownership
94,96 Roadmaster, 69 Wildcat, 95 lesabre , 97 park avenue
IF you want to clean out the cylinders from excessive raw gas, push the accelerator pedal to the floor and that will disable the fuel injectors from pouring more fuel into the combustion chambers when trying to start!. If the plugs are too wet, they may not fire, so you may have to remove them and clean/replace them. In addition, do you have any codes?
It's OBDI , and yes i've tried the paper clip trick but it just triggers my radiator fans.
 
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