Shakes and loss of power

Tiny
RICK RALSTON
  • MEMBER
  • 1994 SUZUKI SIDEKICK
  • 1.6L
  • 4 CYL
  • 4WD
  • MANUAL
  • 140,000 MILES
Starts and runs fine for a few minutes, then shakes and loses power.
MAF, 02 sensor, plugs, wires, distributor cap all replaced.
All plugs are sooty black. What would cause too much fuel to be injected?
Thursday, August 12th, 2021 AT 5:58 PM

14 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
If the plugs are soot covered then that would be too much fuel or unburned fuel from poor ignition.

Here is a guide that will get us started even though it appears you have replaced the basics so unfortunately this won't be the easiest of repairs but I am sure we will find it.

https://www.2carpros.com/articles/symptoms-of-low-engine-power

The shaking is most likely a misfire so I am going to think that we have one of a couple issues remaining. First and foremost leaking injectors or fuel pressure issue. So we need ot start with checking the fuel pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If the pressure is high then that can dump too much fuel. If it is low then it could be leaking injectors.

The next likely issue is the PCM is just commanding the injectors on for too long. Normally it does this due to a faulty sensor but it looks like you replaced the common ones that would cause this.

So how long did it take for these plugs to get fouled?

The last possible cause of soot covered plugs is a timing issue that basically the exhaust valve is opening too soon. So we should check the compression and make sure that is correct.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please run through this info and let us know if you have questions and what you find with it and we can go from there.

Thanks
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Friday, August 13th, 2021 AT 6:21 PM
Tiny
RICK RALSTON
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  • 13 POSTS
Many thanks for your advice. Definitely too much fuel. Smooths out at high speed when the engine can burn the extra fuel. Whatever it is, happens only after warm up. Timing would not go in and out. Compression checked okay. Sounds like the PCM may be the culprit. Is that hard to change out?
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Friday, August 13th, 2021 AT 9:42 PM
Tiny
RICK RALSTON
  • MEMBER
  • 13 POSTS
If the CPM is inside the car, would it's function be affected by the engine heat?
The motor runs fine when cold. After about 10 minutes it shifts to problem mode. Would the PCM do that, or something in between that controls the fuel to all 4 cylinders?
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Saturday, August 14th, 2021 AT 3:44 AM
Tiny
KASEKENNY
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That is great info. This is either a PCM or a sensor that is feeding the PCM faulty info.

So this is called open and closed loop. Basically the engine starts in open loop and runs off a preprogramed set of parameters based on the temperature sensors.

Then the PCM monitors the engine coolant temp and as soon as it is up to operating temperature, it switching to closed loop and monitors the o2 sensor data as well as the other sensors to fine tune the air fuel mixture.

See below for more detail.

What I would do to confirm this is the issue is unplug the o2 sensors and see if this does not happen at all. This should keep the engine in open loop and that would prevent it from acting up.

Do you have a scan tool that we can monitor o2 sensor data? If the o2 sensors are telling the PCM that it is rich then the PCM should be adjusting but if it is not then the PCM could be the issue. However, the PCM may be trying to adjust this but if the injectors are leaking then that would cause this as well. The only thing that doesn't support this is that you would think a leaking injector would not stop just because an o2 sensor is unplugged.

This is why we need to confirm that when changing the state of open to closed loop and back that the issue starts and stops. If it does then the PCM is the issue since you already replaced the o2 sensor.

The only thing that gives me pause is the o2 sensor that you replaced is also faulty but that is unlikely but not impossible.

Let me know if you have questions on this.

Thanks
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Saturday, August 14th, 2021 AT 6:04 PM
Tiny
RICK RALSTON
  • MEMBER
  • 13 POSTS
Problem exist with 02 sensor unplugged. We thought it might be a defective 02 sensor so we replaced it twice. While it had been taking up to 15 minutes to warm up and start shaking the time has reduced to zero. Shakes all the time now. So I guess that means it is the computer that is telling the injectors to stay open too long, right?
Do we have to take the dash apart to replace the computer? What do you think of the rebuilt computers that are offered online for around $200.00?
We have been struggling with this issue for over a month. Your guidance is greatly appreciated.
Rick
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Sunday, August 15th, 2021 AT 2:08 PM
Tiny
KASEKENNY
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Take a look at the info attached below. I have not replaced this on this vehicle but the manual shows it just on the left side of the steering wheel.

If it were me, I would replace this with a rebuilt unit as they are normally sold with a 30 day warranty. So if they are faulty they will change it out. However if it only last a couple years then that is far cheaper then going with a new unit.

Please see the process below for that info.

Thanks
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Sunday, August 15th, 2021 AT 7:57 PM
Tiny
RICK RALSTON
  • MEMBER
  • 13 POSTS
I will try a computer replacement. You have been so very helpful.
Many thanks.
Rick
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Sunday, August 15th, 2021 AT 8:43 PM
Tiny
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Sounds great. Thanks for using 2CarPros.

Clearly not necessary but to help spread the word about the site, if you leave a review on this link below, it will help get it out there.

https://www.sitejabber.com/reviews/2carpros.com

Thanks
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Monday, August 16th, 2021 AT 10:42 AM
Tiny
RICK RALSTON
  • MEMBER
  • 13 POSTS
Testing for connection. I got a "need log" notice.
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Saturday, August 28th, 2021 AT 10:18 PM
Tiny
RICK RALSTON
  • MEMBER
  • 13 POSTS
Hello,

Installed a replacement computer. No improvement.
Car start fine, runs ok for about 20 seconds, then (when over loaded with fuel?) Starts to shake. Since all four plugs are sooty black, me thinks something is regulating too much fuel.
What could it be?
Thanks,
Rick
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Saturday, August 28th, 2021 AT 10:21 PM
Tiny
KASEKENNY
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Oh wow. I figured that would have been it. If that is the case then we do need to confirm a fuel pressure issue. That means we need to check what it is at the rail.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I attached the process below for both the 8 and 16 valve engines depending on which you have.

This would most likely be a regulator issue if you are correct and the fuel pressure should reflect that. Basically if it is high and not limiting the pressure then when the injectors are opening they are spraying too much fuel due to the pressure being too high.
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Sunday, August 29th, 2021 AT 9:21 AM
Tiny
RICK RALSTON
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Things got worse. Fuel pressure checked okay. Pulled plug wires while running. No.2 cylinder made no change with wire out. Spark was good so must be no fuel. My thought that all 4 plugs sooty black meant too much fuel was a mistake. Decided to replace all injectors while at it. Set of 4 injectors cost from $46.00 to $600.00! Bought "reconditioned OEM Nikki" injectors for $96.00. Motor starts but not enough power to move the car. Wrong injectors? Or did we mess something up during the change? Should we try to clean/repair old injectors? Will spending more money on injectors be the answer? We are lost, need your advice. Thanks much, Rick
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Wednesday, September 15th, 2021 AT 9:21 AM
Tiny
KASEKENNY
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At this point we can't rule out the new injectors. So that means what I would do is install the old injectors back in the vehicle solely to confirm the new injectors were causing that issue. However, when putting them back in, swap that suspect injector with another cylinder to see if the issue of it not changing when spark was removed moves to that cylinder.

This is just another way to confirm the injector was the issue but you just purchased some faulty injectors. This way we can confirm two things at the same time. First, the injector was the issue on that cylinder and two that the replacement injectors were faulty.
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+1
Wednesday, September 15th, 2021 AT 10:31 AM
Tiny
RICK RALSTON
  • MEMBER
  • 13 POSTS
Will give it a try. Thanks
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Wednesday, September 15th, 2021 AT 11:11 AM

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