1996 Pontiac Sunfire bucks in 3rd

pontiac
sunfire

#1

1996 Pontiac Sunfire GT 2,4L
manual transmission

When I try accelating in 3rd gear the motor hesitates (bucks) several times. To avoid the problem, I have to give it less gas.

Furthermore, when the engine is hot after having been driven, it is very hard to start.

I have changed the following
fuel filter (2 yrs ago) (MAP senor and sensor just next to it (5 yrs ago), spark plugs, and sensor next to injectors (left side of injectors).

I just ordered ingition coils and will replace next.

Note: No “check engine” light is coming on.

Any suggestions.


#2

Check the throttle position sensor. It should change resistance smoothly as it rotates through its range. I had to clean the TPS on my 1984 Cavalier with an electrical contact spray cleaner.


#3

‎Thanks very the recommendation. I will replace if the ignition coil replacement does work.

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#4

Hard to start when hot — I presume this means it cranks ok but takes a long time to catch – that is often caused by an electrical system problem. Some part is getting hot and temporarily failing. Crank position sensor, cam position sensor, ignition module, coils. Presuming the CEL is not on, there are no diagnostic codes, and the routine maintenance is up to date – spark plugs, fuel filter, exhaust system back pressure – suggest to focus on those components mentioned above of the engine’s electrical system. Any of them could also cause the hesitation.

BTW, keep the old parts you remove on hand. The parts changing method of car repair doesn’t work these days as well as it did on cars of 60’s, 70’s, and 80’s vintage. Easy to run out of money before you run out of guesses. And sometimes the replacement part is faulty, while the part you removed was working fine.


#5

Thanks very much for your advice.

Someone recommended that I change the throttle performance sensor TPS.

I will be charging that next

Best

Robert

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#6

The TPS (Throttle Position Sensor) can be easily tested with an ohmmeter.


#7

Your car has an AIR FILTER as well. Make sure it is not clogged up!

Bonne Chance!


#8

‎Docnick

Merci beaucoup pour la suggestion , je le vérifierai .

Robert

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#9

Sounds like an insufficient supply of fuel, the fuel pump may be failing. Measure the fuel pressure while accelerating, check if the pressure drops.


#10

‎Good point. It is the original fuel pump. The moteur has only 185 000 km

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#11

The engine computer uses that part to monitor how much you are pressing on the gas pedal, and how quickly. That could possibly cause the 3rd gear acceleration hesitation; the problem is the TPS is not a common heat related failure item. As mentioned above, the existing TPS sensor can often be easily tested with just an ohm meter. Especially if it just the variable resistor type. Some are a little more complicated and may require a Pontiac scan tool to test. If you decide you want to try testing it, let us know; someone here likely already knows how to do it, or can look it up.

Please let us know what you discover OP.


#12

‎Will do

Traveling at the moment. Back home on 14 June

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