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Author Topic: Misfire Under Heavy Acceleration  (Read 33912 times)

SuperSport346

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Misfire Under Heavy Acceleration
« on: July 25, 2012, 02:34:00 PM »

My 91 XR2 has what seems to be a misfire that only occurs under hard acceleration, i.e. merging on the highway.  Misfire occurs at >3000rpms.  It doesn't seem to misfire in first gear, maybe only under boost?  It didn't seem to have a problem before I replaced my turbo.  I've also found oil in the intake hose if that's any help.

Other than under hard throttle, it runs like a dream.  I threw new plugs and wires at it with no avail.   :(    I appreciate any help!
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1991 Capri XR2 - Red 5-Speed
2002 Camaro SS - Black 6-Speed
2000 Wrangler - Yellow
2001 Silverado Z71 - Pewter

SuperSport346

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Misfire Under Heavy Acceleration
« Reply #1 on: July 26, 2012, 02:15:00 AM »

Driving around this morning I noticed two things.  First, the "misfire" occurs only when I'm pushing about 10 psi of boost.  Second, the car beeps at me right before it happens.  This makes me believe that it isn't a misfire, but something related to the turbo.  Any ideas?
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1991 Capri XR2 - Red 5-Speed
2002 Camaro SS - Black 6-Speed
2000 Wrangler - Yellow
2001 Silverado Z71 - Pewter

tonlaw71

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Misfire Under Heavy Acceleration
« Reply #2 on: July 26, 2012, 03:05:00 AM »

Yep, you're overboost sensor is kicking in. The beep is the overboost warning signal. Do you have a boost controller installed? If so, you either need to turn down the boost, or disconnect the overboost sensor. If you disconnect the sensor, make sure you don't go above about 11psi unless you have a chipped ECU.
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///Tony aka Bubba Gumpshrimp\\\

///'92 Plasti-Dipped XR2\\\

SuperSport346

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Misfire Under Heavy Acceleration
« Reply #3 on: July 26, 2012, 03:36:00 AM »

As far as I know, I do not have a boost controller or chipped ECU.  What is my easiest/cheapest option here?  I doubt I would be able to stay under 11psi if I just disconnescted the sensor.
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1991 Capri XR2 - Red 5-Speed
2002 Camaro SS - Black 6-Speed
2000 Wrangler - Yellow
2001 Silverado Z71 - Pewter

tonlaw71

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Misfire Under Heavy Acceleration
« Reply #4 on: July 26, 2012, 03:50:00 AM »

Then I'm not real sure why you're overboosting. Did you replace your turbo with another stock one? Was the replacement rebuilt, or off a running motor? The least expensive way to go to control the boost is to get a manual boost controller. Get a decent ball and spring controller. You can get them for around $20 on ebay.
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///Tony aka Bubba Gumpshrimp\\\

///'92 Plasti-Dipped XR2\\\

SuperSport346

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Misfire Under Heavy Acceleration
« Reply #5 on: July 26, 2012, 04:01:00 AM »

I was told it was a stock turbo although I'm not sure the guy I bought it from knew all that much about it.

I will look into one of those boost controllers, are they difficult to install?
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1991 Capri XR2 - Red 5-Speed
2002 Camaro SS - Black 6-Speed
2000 Wrangler - Yellow
2001 Silverado Z71 - Pewter

Rocketman

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Misfire Under Heavy Acceleration
« Reply #6 on: July 26, 2012, 04:05:00 AM »

They're very easy to install. You need to do a few supporting modifications with it, though.

How much boost are you running currently?

Are you running premium fuel? Where is your ignition timing set? Does the engine sound like it's detonating?

Is the oil there from the old turbo? Did you clean out the intake hoses/intercooler when you replaced the turbo? Engine oil in the intake air will lower the octane of the gas and cause problems
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1.8L Turbo All Wheel Drive Capri... the "GTXR2"


tonlaw71

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Misfire Under Heavy Acceleration
« Reply #7 on: July 26, 2012, 04:10:00 AM »

Nope, super easy. Do a search on here or on the Facebook pages for details. The easiest place to install it is in the hose going from the crossover pipe to the waste gate. Takes about 5 minutes. Also, I was thinking your waste gate may not be opening when it should which could be causing your over boost issue. Did you check the actuator rod before you installed the new turbo to make sure it was moving? If that is the problem, a boost controller won't help.
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///Tony aka Bubba Gumpshrimp\\\

///'92 Plasti-Dipped XR2\\\

tonlaw71

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Misfire Under Heavy Acceleration
« Reply #8 on: July 26, 2012, 04:16:00 AM »

Yeah, forgot to mention that about the oil. Very important to clean out the intercooler and pipes. Do you think it could be the waste gate, Matt?
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///Tony aka Bubba Gumpshrimp\\\

///'92 Plasti-Dipped XR2\\\

SuperSport346

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Misfire Under Heavy Acceleration
« Reply #9 on: April 29, 2013, 12:41:00 PM »

Can somebody link me to a thread with pics/instructions on how to install a boost controller?  I installed one per the manufacturer's vague instructions, and it did not solve the problem.  I tried searching with no luck yet.

I have not checked the actuator rod on the turbo.  Can it be moved by hand while installed?

I think the oil is left from the old turbo.  I haven't driven the car a whole lot since the new one was installed.
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1991 Capri XR2 - Red 5-Speed
2002 Camaro SS - Black 6-Speed
2000 Wrangler - Yellow
2001 Silverado Z71 - Pewter

SuperSport346

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Misfire Under Heavy Acceleration
« Reply #10 on: April 29, 2013, 12:52:00 PM »

Ok, I installed it where it is indicated in this picture, where another member recommended install.

 

I turned it all the way down per manufacturer instructions, and the overboost controller still kicks in around 8-10psi on the stock gauge.  I know stock gauges aren't the most accurate, but I don't want to spend the money on an aftermarket one at the moment.

What "supporting modifications" should be done, rocketman?

The MBC instructions said to disconnect the stock system, which I did not do.  I'm not finding anything about doing that here on the forum.  Maybe that will solve the problem?  I don't want to take any risks though...
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1991 Capri XR2 - Red 5-Speed
2002 Camaro SS - Black 6-Speed
2000 Wrangler - Yellow
2001 Silverado Z71 - Pewter

Gostlrs

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Misfire Under Heavy Acceleration
« Reply #11 on: April 29, 2013, 04:40:00 PM »

What MBC did you get, Some are crap.

To see if you might have a boost leak or if the wastegate / MBC is bad do this.

Take the vacuum line from the boost source (your red arrows) to the wastegate. Run it. should only be 5-7psi. If it goes higher, then you have either a boost leak somewhere or the actuator is not opening.

So if that is good...you can assume that your MBC is bad or you don't have it set up correctly.

   

That is how it should look set up.

You need a gauge if you are going to raise the boost. They are cheap. You can get a manual sunpro one for 20-25 bucks.

The boost cut is located here. Unplug it.
   

I would not do that until you get your boost gauge & you know your boosting a steady 7-8 psi every time.

You can run about 9 psi without the rocketchip & up to 12 with it installed.
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Gostlrs

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Misfire Under Heavy Acceleration
« Reply #12 on: April 29, 2013, 04:45:00 PM »

If you have this style, they are crap IMO & I have never had one work right.

   


This guy here is a member and sells them.
 http://tunerfixx.com/store/index.php?main_page=product_info&products_id=1

or

I been using this lately on my boosted cars.
 http://prosportgauges.com/manual-boost-controllers.aspx

Love it, small, looks nice, cheap, good warranty & love their Evo Series Gauges too.
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Rocketman

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Misfire Under Heavy Acceleration
« Reply #13 on: April 29, 2013, 06:18:00 PM »

Whoa there Jamie, I missed something early in this thread. This is not a boost controller issue, it's a boost creep issue.

You're experiencing boost creep for some reason, do you have a large exhaust installed? If not, it could be an issue with the wastegate, vaccum/boost reference issue, etc.

A boost controller will only raise the boost level above the baseline boost, it will not lower it at all. If you're overboosting without the controller, it's not going to help.

I would STRONGLY RECOMMEND leaving the boost cut switch connected until you sort out what is causing the boost to creep that high.
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Gostlrs

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Misfire Under Heavy Acceleration
« Reply #14 on: April 30, 2013, 06:59:00 AM »

That is why I said to run it without the MBC. It will give him a idea of what his problem is. If everything is steady without the MBC installed. Then the MBC is the issue.

If it still hits boost cutoff then yes, he has a issue. Boost leaks, bad wastegate, ect.....
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2015 Chrysler 300
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1992 240sx Convertible
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