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Old 06-15-2006, 10:25 PM   #1
bonfireking
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Default 97 DOHC SC2 hesitation/power loss

Howdy, thanks for being here!

It just doesn't want to go in the low RPM range, and doesn't want to get up a hill. This started a month ago and has gotten progressively worse. From researching this forum my first pick is the ECTS.

It seems the engine isn't getting enough gas. Sure enough, the check engine light shows a lean condition with a code checker thingy. I've got Platinum plugs with 70k on them (but they look good and gapped at .040), 70k on the wires (they also look good), and a new fuel filter. Also put in STP injector cleaner last oil change 1k miles ago with no positive result.

In addition to a new ECTS (never done to this car with 150k on the ticker) I'm going to check the injectors for deposit buildup.

What other troubleshooting can I do to narrow this lean condition down to the source?

Thank you!

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Old 06-15-2006, 10:56 PM   #2
Nowhere Man
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Default Re: 97 DOHC SC2 hesitation/power loss

From what I've heard, the DOHC engines do not like platinum plugs, but it may vary by brand. Just curious, what brand plugs are you using?

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Old 06-15-2006, 11:12 PM   #3
bonfireking
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Default Re: 97 DOHC SC2 hesitation/power loss

That's an interesting bit of info.

They're Bosch plugs. I also have a non-platinum set of Autolites (stock temp) that I'll put in while I'm at it to see if there's any change.

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Old 06-16-2006, 08:46 AM   #4
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Default Re: 97 DOHC SC2 hesitation/power loss

The Bosch plats should be replaced. Autolites are okay, NGK copper or V-Power are recommended. If you've never replaced the ECTS, do it. However, typically the ECTS causes the engine to run rich rather than lean. Are you idling high? When was the last time you replaced your fuel filter?

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Old 06-16-2006, 07:43 PM   #5
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Default Re: 97 DOHC SC2 hesitation/power loss

Just replaced the fuel filter a thousand miles ago (same time I added that injector cleaner).

I'll store the platinums and put in the Autolites while I'm doing this ECTS.

I'll crank er up and let you know if the problem persists.

I thank both of you for the replies!

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
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Old 06-16-2006, 08:44 PM   #6
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Default Re: 97 DOHC SC2 hesitation/power loss

OK, just put in ECTS and BarnOwl was right: that didn't fix it. Still 'feels' to be lean, like I'm not getting enough gas.

Put in Champion plugs, gapped at .040 as suggested by NowhereMan, that certainly helped but the hesitation remains.

I would like to bench test the injectors, does anyone know of a way to do this? I have infinite power supplies, especially 12 VDC. Can I pull the fuel rail, pressurize with fuel, and apply 12V to an injector to get it to fire?

I'm concerned about the injectors. When I replaced the ECTS I pulled off the breather. Where it connects to the intake I realized the rubber was folded back under the clamp from the last time I had the breather off. This was allowing a small amount of unfiltered air into the intake. I'm guessing this COULD foul the injectors somehow.

Any ideas from the pros on my next troubleshooting step???

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
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Old 06-17-2006, 06:40 AM   #7
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Default Re: 97 DOHC SC2 hesitation/power loss

It's probably time you got your hands on a fuel pressure gauge. There are a variety of tests you can do to determine if you're leaking pressure somewhere. There are those that will tell you anything but Techron for fuel injector cleaning and you might as well pee in the tank. So, you could try that (The Techron not peeing. ). There is a tester called a noid light that's for checking injectors. I've never used one, but you might see if you can borrow or rent one somewhere. You can listen to the injectors with a mechanics stethoscope and make sure they are clicking nice and regularly.

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Old 06-17-2006, 11:30 PM   #8
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Default Re: 97 DOHC SC2 hesitation/power loss

Of course, I wanted to fix all the cheap possibilities first, so I just replaced the TPS. While I had the throttle body off I looked in the intake and it's covered in 1/8th inch of carbon...

1) Is this normal for 150k miles?
2) What's the easiest way to clean it? Can I remove the intake without taking off the head? Per the advice in this thread, I'm advising the wife to only fill er up with Chevron's Techron, but how can I clean the injectors fast/now?
3) Is this an indication of carbon-clogged injectors?
4) What's the best way to clean out this carbon, cuz now I know the valves are bound to be covered in this same layer of carbon and may not be seating properly (leading to my hesitation problem).


While I'm at it, I sure do appreciate everyone's input into this problem!

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
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Old 06-17-2006, 11:48 PM   #9
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Default Re: 97 DOHC SC2 hesitation/power loss

I would first do a compression test...

And inspect your exhaust for leaks near the head or for a clogged cat.

Also, could be a bad map sensor forcing lean... but could just be something as simple as that EXCESSIVELY dirty throttle body.....

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Old 06-17-2006, 11:57 PM   #10
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Default Re: 97 DOHC SC2 hesitation/power loss

Quote:
Originally Posted by Bigdaddy94sc2
I would first do a compression test...

And inspect your exhaust for leaks near the head or for a clogged cat.

Also, could be a bad map sensor forcing lean... but could just be something as simple as that EXCESSIVELY dirty throttle body.....
Interesting... the exhaust hasn't been looked at yet. I'll try that. I know the manifold isn't leaking at the head, but I'll see what I can find out about the cat, haven't thought of that.

I didn't think a MAP sensor would force the lean condition, I'll try replacing that next week when Saturn is open again.

I'm a clean-freak and can't stand the dirty intake. I want to clean it (have the machinist give it a warm bath) but I'm not sure I can get the intake off without taking the head off.

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
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Old 06-18-2006, 12:19 AM   #11
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Default Re: 97 DOHC SC2 hesitation/power loss

Intake isnt very hard to take off... Just undo the fuel lines, the throttle cable, the injector harnesses, and take the nuts off. Not the easiest thing to do in your driveway, but not the hardest by far!

Another thing to check is to see if the EGR is stuck open, or excessively dirty as well. Not as probable, but something to check out as well....

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Old 06-18-2006, 01:03 PM   #12
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Default Re: 97 DOHC SC2 hesitation/power loss

The carbon on the throttle is normal if you've never cleaned it. Get hold of some carb cleaner or my favorite Deep Creep and clean it up. Whatever you get make sure you get something that's safe for O2 sensors. That carbon would burn off the valves. The manifold is s PITA to get off. Get the engine hot and with the car running, slowly pour a bottle of Sea Foam or MMO into the PCV valve hose. Don't do this too fast and keep the engine running. The car will let out a lot of really cool smoke, but this should clean the carbon out.

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Old 06-18-2006, 09:14 PM   #13
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Default Re: 97 DOHC SC2 hesitation/power loss

Hey, having a newborn can be handy! I used one of his old medicine syringes to get the seafoam into the PCV hose. Got the whole can in there and there's still some hesitation. But I've got it in my head that fouled injectors are the problem (judging by the carbon covered intake).

I'm probably going to try another can of seafoam tomorrow. Then I'm contemplating removing the intake and sending it in for a good cleaning. Of course I'll service the injectors at that point.

Barnowl and everyone, I sure do appreciate your help. Send me any ideas if they come up, I'll be here trying to help the other folks.

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
I'll find more when I mow.

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Old 07-01-2006, 10:07 PM   #14
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Default Re: 97 DOHC SC2 hesitation/power loss

Hey Barnowl, I finally got a pressure gauge. With the engine running I'm showing 20 psi whether wide open or idle (BTW, getting to wide open is difficult since she just doesn't want to get up there). How does that 20 sound?

I'd like to do a leakdown test. How long should the pressure remain after I shut off the engine?

Bigdaddy, I'm also thinking the MAP sensor since I still have this hesitation problem after bench testing the injectors. You mentioned checking the cat, how can I do make sure it's flowing well?

BTW, in testing the injectors, I pressurized them with Seafoam and an old fuel pump, then fired them with the battery. All injectors worked well and got a good internal cleaning, they spray nicely.

Thanks for the input everyone!

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
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Old 07-01-2006, 10:34 PM   #15
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Default Re: 97 DOHC SC2 hesitation/power loss

20 PSI sounds really bad. The car should barely start with that never mind drive.

The operating pressure of the fuel system is 40-55 PSI.

You have a bad fuel pump, clogged fuel filter or a pressure regulator that is letting fuel by at to low a pressure or a bad pressure reading.

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Old 07-02-2006, 12:40 AM   #16
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Default Re: 97 DOHC SC2 hesitation/power loss

Quote:
Originally Posted by ssicarman
20 PSI sounds really bad. The car should barely start with that never mind drive.

The operating pressure of the fuel system is 40-55 PSI.

You have a bad fuel pump, clogged fuel filter or a pressure regulator that is letting fuel by at to low a pressure or a bad pressure reading.

OK, I'll rule out the filter since I just changed it (the filter was a 'first guess' when this problem started). My big question is whether or not the MAP sensor could cause the regulator to decrease pressure. I would figure if the reading from the MAP is off, the computer could be telling the regulator to do the wrong thing.

Any arguments on this thinking?

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
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Old 07-02-2006, 01:07 AM   #17
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Default Re: 97 DOHC SC2 hesitation/power loss

The MAP tells the fuel pressure regulator nothing. The pressure reg is a mechanical device with no feedback to the PCM. It regulates fuel pressure by reaction against a spring and a vacuum valve (in your 97).
I would put the regulator low on the list just because they do not fail very often. The fuel pump especially on the 97's (they have a know problem in many of the pumps) would be the likely source of the problem.
You could eliminate the regulator by checking the pressure with the fuel return line blocked off.
This is hard to do becase you can't pinch off metal fuel lines and the plastic ones will be ruined if you pinch them off.

Safety Note
Do not pinch off the plastic fuel lines at all. You will compromise them. They can not be properly repaired--if at all--and are only availible as complete lines from the tank up.

The proper way to block the return line off is to remove it from the fuel rail and install a block line onto the return line at the fuel rail.

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Old 07-02-2006, 02:02 AM   #18
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Default Re: 97 DOHC SC2 hesitation/power loss

I am somewhat suspect of that fuel pressure reading. The car would barely do more than idle if the pressure was really that low. Reading the original post, and considering the miles on the car (150k) my first suspect is also a CLOGGED exhaust. Especially if at WOT (wide open throttle) you do not see an improvement as the MAP sensor data is all but ignored in favor a preprogrammed operational parameters set by the PCM anytime the throttle setting is at ~80% or higher.

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Old 07-02-2006, 08:59 AM   #19
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Default Re: 97 DOHC SC2 hesitation/power loss

To test, I'll break the exhaust apart before the cat... is that a valid test?

As far as the pressure reading, I may have done it wrong. I cranked the car, got it warm, then screwed on the pressure gauge. It showed 20. Now that I think about it, I didn't purge it. From your replies I think I need to try again.

Forgive my simple mistakes, I'm more a carbed V8 kinda guy. And the only sensors I'm used to are for gauges, not PCMs.

Thanks again for all your help!

...
'97 SC2, 200k, rebuild in process
'00 Honda Civic EX, 180k
'87 GMC S15, 80k
'84 Mustang, can't wait to rebuild [again]
'03 Honda CrV, 80k
I'll find more when I mow.

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Old 07-02-2006, 11:08 AM   #20
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Default Re: 97 DOHC SC2 hesitation/power loss

You can pull out the O2 sensor for a little bit to see if you have a clogged cat.

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