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Dan
Dan, Auto Service Technician
Category: Car
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Experience:  GM ASEP A.A.S. 14 years GM experience. Mark of Excellence and Professional Guild awarded.
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1995 Buick LeSabre: I rev..V6..it starts to sputter and the rpms drop

Customer Question

if I rev up my 1995 Buick LeSabre (3.8 L V6) steadily up. At around 4000rpm it starts to sputter and the rpms drop then surges up again. It does this surging continuously. Lately the car has been stalling, at no particular time. Sometimes @55 mph, sometimes stopped at a light, sometimes accelerating. The plugs, coils and wires are new. The check engine light comes on but when the key is turned off the light resets and is out (until it hesitates or stalls)...any ideas?
Submitted: 7 years ago.
Category: Car
Expert:  Dan replied 7 years ago.
First I would scan the computer and find out what trouble codes are setting. They are hard faults which indicate or at least will point you in the right direction to diagnose your problem. Have you changed the fuel filter lately? Does the exhaust smell like rotten eggs or seem to be choked? Sometimes if the engine is running lean from a plugged fuel filter or exhaust it will smell like that and the check engine light will come on indicating lean or give oxygen sensor code(s). Check this out and start by checking for codes. Then do a thorough visual inspection of the engine and let me know what you find ok.
Customer: replied 7 years ago.
The car is a crossover year for the obd system, it is OBD I compliant, but has an OBD II connect. No one has been able to scan the computer for codes. I don't think the exhaust smells, but I don't know what you mean by "choked".. This made be a stupid question but would the fuel filter be the cause of the surging at high er rpms?
Expert:  Dan replied 7 years ago.
It could cause a misfire that feels like a surge and also feel like a miss that gets worse under load. You may also want to check the transmission fluid for color, smell and level as a transmission slipping and/or shuttering will cause this (a slipping torque converter).
Customer: replied 7 years ago.
Changed the filter to no effect, Tranny fluid color is red and has no burnt smell, level is fine.The car stalls out, but at no particular time. I mean I could be doing 70mph and it stalls or I could be accelerating from a stop when it stalls or I could be moving along at 30 mph. THe same holds true for when it misses. When it does miss and or stall the tach goes wacky, the voltage, fuel and temp lights flash and the change oil soon light comes on as well as the check engine light comes on. The car always restarts (with the check engine light not on until it acts up again). Besides that my water temp climbs over 200 (with a 180 thermostat) and my dash volt gauge read under 13 volts (but the reading at the battery is 13.98 volts.....I also have a new belt, alternator and water pump.
Expert:  Dan replied 7 years ago.
Have you checked the battery cables for being clean, tight and corrosion free? Is the cooling system full and completely bled of all air? Sometimes if there is air in the system it will cause erratic temp. spikes but when the air is completely purged using the bleeder valve by the water pump it should fix that (if it's air in the coolant). Check these out and let me know ok. I have seen where loose or corroded battery terminals will cause stalls, driveability issues and the electrical to go bonkers.
Customer: replied 7 years ago.
Reply to Dan's Post: I've cleaned,tightened, recleaned and retightened the battery cables as well as the ground cables that connect on the inner fender on the passenger's side.I've also unplugged and replugged the connectors on the computer. This car has a bleeder screw on the thermostat housing and when I changed the thermostat (to 180 degrees instead of 195 degrees) I bled the air out of the system. But I will check that again. Anymore ideas on the hesitation/stalling issue? When I floor (in park) the pedal the car "bogs" down (makes a throaty sound with no appreciable gain in rpms) then it will rev up. Hope to hear from you soon.
Expert:  Dan replied 7 years ago.
Now keep in mind there is a rev limiter that protects the engine and will cause the engine to almost bog then accel then bog etc.etc. If the engine doesn't rev higher than say 1000 RPM then check the exhaust for a restricted cat. converter (the best way to check for this is to remove the front oxygen sensor and run a backpressure test. It measures the restriction if any in the exhaust). The reading shouldn't be higher than 2 psi at 1000 RPM. A restricted exhaust will be as high as 10-12 psi and the most likely cause is a plugged cat. converter. This would cause low power, possibly a miss or sag in the engine and would definitely bog the engine down. Also, did you ever check fuel pressure?
Customer: replied 7 years ago.
Reply to Dan's Post: Checked the fuel pressure...it was 35 at idle and went up at 38 at 3000rpm.......the engine revs to 4000rpm before it starts it rev then bog then rev thing so I don't think it's too much back pressure.
Expert:  Dan replied 7 years ago.
I would really try to get that trouble code as it may lead you to the source of this problem or at least point you in the right direction. Has the fuel filter been changed? Try tapping on and wiggling the engine computer connections to induce a stumble or stall by the engine because an internal computer circuit board that seperates or flexes from heat after driving a while will cause these conditions also. Check this out and try using a hairdryer on the computer (using judgement not to cook the computer) to induce heat-like conditions.

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