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Old 07-21-2011, 02:57 PM   #1
raj49
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Mad Hesitation/poor acceleration

2001 SC2 91k miles. Symtoms occur only after engine reaches normal operating temp. Hesistates during low rpm then runs better.
Replaced ECT with a BWD WT5029 sensor. Old one had a hairline crack on it. No change. Temp gauge goes to half way mark and fan kicks on at about 221 deg. I assume thermostat is working.

KOEO fuel: 50 psi
KOER fuel: 50 psi
I was able to read fuel pres when test driving and fuel remained at 50 psi. Chilton manual says 40 to 55 psi so Im guessing pump is good. Had some trans work done and they replaced the TPS.
I have a good working 99 SL2 to swap wires and coils with to narrow down problem.

Any other suggestons appreciated.

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Old 07-21-2011, 03:19 PM   #2
blue92
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Default Re: Hesitation/poor acceleration

since you got the wires and coils, go ahead and swap them.
Does your Cat rattle? Might be plugged.

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Old 07-21-2011, 03:26 PM   #3
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Default Re: Hesitation/poor acceleration

Cat doesnt seem to rattle. Just waiting for everything to cool down a bit before swapping.

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Old 07-21-2011, 06:13 PM   #4
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Default Re: Hesitation/poor acceleration

Swapped plugs, wires, coils each one by one and drove.

No dice.

Still havin that hesitation. I guess next step is fuel filter/regulator then pump maybe.

Anyone have any thoughts?

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Old 07-22-2011, 08:16 AM   #5
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Default Re: Hesitation/poor acceleration

Any suggestions please?

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Old 07-22-2011, 08:26 AM   #6
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Default Re: Hesitation/poor acceleration

clogged cat would likely cause problems at higher RPM, same with the fuel pump/regulator/filter.

how does the ECTS plug look, any corrosion?

you said the TPS was replaced, but have you tried swapping it with the one from the parts car if it's the same?

try swapping the EGR valve if it's the same.

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Old 07-22-2011, 08:30 AM   #7
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Default Re: Hesitation/poor acceleration

Tried swapping the TPS but a tab is on opposite side on connector. Gonna try EGR.

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Old 07-22-2011, 08:40 AM   #8
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Default Re: Hesitation/poor acceleration

Try swapping out the crank position sensor. They are known to show signs of failure when heated up. Its on the backside of the motor , behind the starter. One bolt holding it down. It is a long black plastic tube looking thingy.

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Old 07-23-2011, 01:35 PM   #9
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Default Re: Hesitation/poor acceleration

Swapped CPS, no change, swapped EGR, no change, drove with front O2 sensor off, no change. Injector's measure about 13.1 to 13.5 ohms IIRC.

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Old 07-24-2011, 04:44 PM   #10
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Default Re: Hesitation/poor acceleration

Could fuel pump or filter/regulator be bad even if pressure is 50 p.s.i during the faulty condition?

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Old 07-24-2011, 05:04 PM   #11
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2001 SC2
Default Re: Hesitation/poor acceleration

How does it hesitate when it is running? Running poor at idle but runs good above idle makes me think vacuum leak.

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Old 07-24-2011, 05:11 PM   #12
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Default Re: Hesitation/poor acceleration

My first thought was vacuum leak but cant seem to locate any. It dosent accelerate after about 10mph but suddenly would start goin after 5 10 seconds.

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Old 07-24-2011, 06:03 PM   #13
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2001 SC2
Default Re: Hesitation/poor acceleration

In park or neutral, can you rev it to fuel cutoff like normal? If its not a vacuum leak then Blue92 may be on to something with the clogged cat idea. Usually a clogged cat will not let the rpms over 3000 or 4000 even with your foot at WOT.

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Old 07-24-2011, 07:17 PM   #14
magtec
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Default Re: Hesitation/poor acceleration

are you sure it's the engine and not the transmission slipping?

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Old 07-24-2011, 11:46 PM   #15
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1999 SL2
Default Re: Hesitation/poor acceleration

The '99 TPS will work for the '00+ models, and vice versa. I found this out the hard way because O'Reilly lists the '00 TPS for a '99 DOHC, but the correct TPS for the '99 SOHC. Since there were no others available locally, I chanced it and broke the tab.

I actually like the TPS for an '00 on my '99, even though not originally spec'd for one. The two engines are otherwise pretty much the same, and, from what I gather, they flattened the TPS curve a bit for '00 to improve emissions, because the earlier TPS was over-shooting by having too much change in the low end. I find that acceleration is far peppier, and my MPGs increase by at least 1 with this in place, since fuel prediction is more accurate. ST FTRM numbers stay closer to 0 on acceleration.

Of course if you have a TPS from a '99 car, and you have a '00+, you might notice the opposite effects. Still, it should work well enough for you for now.

If you want to test your old TPS, connect your ohmmeter to the center terminal (unplugged from car), and to each of the side terminals, one at a time. Move TPS through its range of motion and watch meter. Resistance should change smoothly and start and stop in the exact same place. Jumping around and not beginning and ending the same every time indicates a worn control. Replace.

If both of the EGR valves you are using are used, it might be wise to check the position indicating potentiometer (center three terminals). Test this like you test a TPS, and move the pintle in and out. If the computer can't tell where the EGR valve is at, inaccurate opening will result, which will result in a loss of power.

...And, of course, there could be many other causes, such as a slipping transmission, which was suggested earlier. A MAP sensor that is failing and/or not connecting to the plug correctly will cause hesitation/poor acceleration. It also never hurts to really clean the injectors well, in any case.

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Old 07-25-2011, 08:17 AM   #16
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Default Re: Hesitation/poor acceleration

Definetly not a slipping transmission.

EGR form the 99 was brand new from ebay. Not getting any DTC's. I will check TPS the way u suggested. Again, not getting any DTC's. I'll have to check when hot since thats when its occuring.

I'll take it down to midas to check for clogged cat. I drove with fron O2 off but it still had the hesitation.

Was going to ask this earlier but forgot, where is the MAP on the 2001? On the 99 sl2, its on top right of intake. But i dont see it for the SC2.

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Old 07-25-2011, 08:59 AM   #17
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Default Re: Hesitation/poor acceleration

There are many posts about the poorly assembled intake manifold gasket leaking by cylinder #1. Spraying fluid in and around the intake manifold gasket with the engine idling can verify a vacuum leak. It might be worth your time to check for a deformed gasket.

This isn't a map sensor issue.

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Old 07-25-2011, 09:20 AM   #18
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Default Re: Hesitation/poor acceleration

Quote:
Originally Posted by fdryer View Post
There are many posts about the poorly assembled intake manifold gasket leaking by cylinder #1.
What years does this apply to? I found a DIY for one with the aluminum intake but mine has the composite intake. I'll check it anyway.

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Old 07-25-2011, 09:42 AM   #19
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Default Re: Hesitation/poor acceleration

Search, as I recall, from '99(?) to '01.

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Old 07-25-2011, 10:54 AM   #20
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Default Re: Hesitation/poor acceleration

That was gen-3 (2000-2002) SOHC ONLY.

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