Intermittent hesitation and RPM surge, no codes

Tiny
MIKESMARINEANDDELI
  • MEMBER
  • 1996 CHEVROLET BLAZER
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 110,000 MILES
First there was severe hesitation under load. Now hesitation seems to be less. But there is a rough idle. And rpm surging. Put it into reverse for example and the rpms increase significantly before going back down. These problems are only intermittent and there are never any trouble codes thrown. Check engine light comes on sometimes but does not stay on. I have put a scanner on it. Fuel trims seem fine. Except my scanner shows a couple of short term fuel trim listings beyond the two short and long term trims of both banks. I think these are listed as short term fuel trim bank 1. S2 and S3. And they both show a stable 99.3 percent. I take these are irrelevant for this vehicle? I have changed and cleaned the MAF sensor twice. Measured voltages with volt meter. Changed plug wires and plugs were changed last year. Changed Inlet air temperature sender. Checked battery connections. Alternator fine. EGR tests fine. Replaced map sensor. I did carburetor spray to check vacuum leaks. Nothing. When idling fine vacuum gauge is steady near 20 psi. I have a backup idle air control sensor and cam position sensor and coolant temperature sensor I will replace tonight. After that, I do not know what to do or think next. Any thoughts or ideas would be greatly appreciated. Thanks.
Tuesday, April 10th, 2018 AT 7:32 AM

17 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon.

What are the long term trims for bank 1 and bank 2 upstream O2 sensor?

Check the fuel pressure. you may have a bad fuel pressure regulator leaking fuel into the intake system.

Roy

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Tuesday, April 10th, 2018 AT 1:39 PM
Tiny
MIKESMARINEANDDELI
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Hi Roy. I am just getting use to this new scanner the long and short term fuel trims showed near 0 at idle and when accelerated never got too much beyond 20 pc or so What would the 02 sensor reading look like on the scan tool? Longftb102? I thought it was acceptable. But I will do another test tomorrow with the numbers. I did a fuel pressure test. It was 60 psi plus and held solid for over five minutes.
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Tuesday, April 10th, 2018 AT 2:13 PM
Tiny
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Okay.

The long terms only are what I need. They should be around seven to eight percent idling.

The regulator can still be leaking fuel into the intake. That is why I need those trims.

Roy
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Tuesday, April 10th, 2018 AT 2:27 PM
Tiny
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  • 9 POSTS
Girlfriend claims this problem happens mainly cold during startup and shortly thereafter. She also says she smells raw fuel near tailpipe. I have never smelled raw fuel myself. When the severe hesitation was more prevalent the engine was hot and under load. Last year I changed the intake gasket. Thinking I did not get a clean seal somewhere I was always concerned with a vacuum leak. But I have done countless tests and I cannot hear any whistle or rpm change during spray event.
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Tuesday, April 10th, 2018 AT 2:44 PM
Tiny
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The regulator is inside the plenum. You will not see it at all.

That is why I need those numbers as the smell of fuel concerns me.

Roy
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Tuesday, April 10th, 2018 AT 2:48 PM
Tiny
MIKESMARINEANDDELI
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Regular long term fuel trims on both banks at idle are roughly -3.1percent. That is live data from a review. I am not near the vehicle until tomorrow to reconfirm these readings.
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Tuesday, April 10th, 2018 AT 2:50 PM
Tiny
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Okay, keep me updated.

Roy
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Tuesday, April 10th, 2018 AT 2:52 PM
Tiny
MIKESMARINEANDDELI
  • MEMBER
  • 9 POSTS
Good morning Roy. Vehicle started and idled very rough this morning. Changed out idle air control, cam position sensor and coolant sensor. Throttle position sensor all parts came off a low mileage Blazer. 60,000 miles. Still idles rough. Surging back and forth. Acceleration seems smooth. I do not smell raw fuel. Long term fuel trim 1 reads 3.9 at idle. Trim 2 reads 2.3. All the 02 sensors are under 1 volt. Why does my scanner show. SHRTB1S2. 99.2 constant. Ditto for B1S3.?
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Wednesday, April 11th, 2018 AT 9:38 AM
Tiny
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Okay, bank 2 sensors have one job they monitor the catalytic converter. They have no control over fuel control that is why you see the 99%.

There is no bank 3 sensor.

Trims look good.

Have you had the injectors cleaned? No additives as they have no effect. This is a procedure that disables the fuel pump and uses the pressure test port to add a cleaner that will clean the injectors directly. The engine runs until the cleaner is exhausted and then you can return the system to the fuel pump.

Roy
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Wednesday, April 11th, 2018 AT 9:45 AM
Tiny
MIKESMARINEANDDELI
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Hi Roy. I was phoning around for injector pressure cleaning. I described all the symptoms of this vehicle to a mechanic that has worked on these vehicles often. He told me not to waste my money trying to clean these poppet injectors. He said over time the springs stick and they start spraying irregular patterns etc. He said replacing the entire spider system is the only fix. Another wonderful design by GM ENGINEERS.
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Wednesday, April 11th, 2018 AT 1:01 PM
Tiny
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I disagree. That person most likely has never cleaned injectors with this equipment. I have done this service hundreds of times with great results.

Engineers have not done this at all. It falls back on fuel. The fuel is what contaminated the injectors, not engineering.

Roy
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Wednesday, April 11th, 2018 AT 1:08 PM
Tiny
MIKESMARINEANDDELI
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Oh my. Okay. Thanks for the info. I guess I'm back to injector cleaning. With the cost being around $125 to $200. I think I'll go online and buy my own pressure injector cleaning kit. Thanks again. Keep u posted.
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Wednesday, April 11th, 2018 AT 1:14 PM
Tiny
ASEMASTER6371
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OK, Borg Warner makes a great lit. They provide the cleaner as well.

Roy
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Wednesday, April 11th, 2018 AT 1:18 PM
Tiny
MIKESMARINEANDDELI
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Thanks Roy. Hope I can find it up here in the North(Canada). We have diddly Squat up here.
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Wednesday, April 11th, 2018 AT 1:21 PM
Tiny
ASEMASTER6371
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Your welcome, keep me updated.

nice kit

https://www.amazon.com/Wisamic-Automotive-Non-dismantle-Injector-Throttle/dp/B075KPD5S2/ref=sr_1_1?ie=UTF8&qid=1523478408&sr=8-1&keywords=fuel+injection+cleaning+kit
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Wednesday, April 11th, 2018 AT 1:28 PM
Tiny
MIKESMARINEANDDELI
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Thanks Roy. Have a wonderful Day. GO JETS. (Winnipeg)
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Wednesday, April 11th, 2018 AT 1:48 PM
Tiny
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Your welcome.

Roy
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Wednesday, April 11th, 2018 AT 1:52 PM

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