2003 GT spark knocks bad

03_TrueBlue_GT · Jul 27, 2011

Guys my GT is spark knocking really bad when Im in 5th gear or any gear when there is a medium load on the engine for example like 4th gear at 35mph it spark knocks or when I add more than a 1/4 of the throttle when its in 5th gear.

I put the car back to stock on the SCT Tuner except I went through the tuner and did the strategy tune , the only thing I changed was that I kept the rear end axle ratio at 3.73 because of the gears. I even put the stock intake back on the car and its still doing it.

What are my options right now? I was told that I should get some throttle body cleaner to clean the throttle body and the MAF. Is the MAF the wire mesh thing that goes in between the intake filter and sensor? Also should I get some seafoam or get octane booster and add it to the gas tank? Right now I have a full tank of 87 octane fuel in the car.

It wont spark knock when I drive the car normally, it only does it when the cars engine is under a load in 3rd of 4th gear and i have the pedal 3/4 of the way or at wot starting out at around 2000-2500rpms or when I add 1/4 of the throttle in 5th gear at 1500rpms it spark knocks bad.

Also I might add that the car has Bosch Platinum spark plugs in it and they have about 30,000-32,000 miles on them.

Thanks for the help guys I really appreciate it, I just want to drive my Mustang without fear of destroying my motor.

trinity_gt · Jul 28, 2011

1) Use a dedicated MAF cleaner and don't clean the throttle body. There are zero benefits to this and a risk of screwing up the car's idle.
2) Check the operation of the EGR system. Make sure it's working.
3) Verify you're not getting excessive oil/vapor entering the intake through the PCV system.
4) Verify the spark plugs are of the correct heat range.
5) Verify cooling system function.
6) On the stock tune you should be able to run 87 without detonation. If all else is fine (plugs, EGR, PCV etc) then you might consider a decarboning. Not likely on fuel-injected cars but if you've got incandescent carbon glowing in the combustion chamber it can cause pre-ignition or contribute to detonation. You might get an idea of chamber carbon from (a) the condition of the plugs and (b) a compression test.

wmburns · Jul 28, 2011

+1 on everything above. Excellent suggestions!

Not a bad idea to confirm the fuel pressure. When was the last time the fuel filter was changed?

Check for exhaust blockage or bad cats (long shot).

I would like to know if there's any improvement if higher octane fuel is used. I can't help but thinking that the stock tune has been altered.

Even if it hasn't, it will provide information and the cleaning offered by a name brand high octane gas can't hurt.

trinity_gt · Jul 28, 2011

wmburns said:
+1 on everything above. Excellent suggestions!

Not a bad idea to confirm the fuel pressure. When was the last time the fuel filter was changed?

Check for exhaust blockage or bad cats (long shot).

Great points wmburns.

OP: Any error codes present in the PCM (e.g. lean indications?)

joshjwc9 · Jul 28, 2011

My vote is fuel filter or plugs. I have not had good luck with Bosch plugs..one blowout and better mileage with the OEM Motorcraft/Autolite replacement.

If the filter hasn't been changed since you had the plugs installed, just change it out so it is a known good FF, they are cheap and might be your problem.

03_TrueBlue_GT · Jul 28, 2011

I changed the fuel filter about 2500 miles ago so it shouldn't be the problem. I did some more resaerch and found that these motors are picky about the kind of plugs that should be used. I went ahead and purchased some oem motorcraft spark plugs and I'm putting them in the car right now. I'm glad that these mod motors have the plugs sitting on top of the engine...

03_TrueBlue_GT · Jul 28, 2011

Update so far...

I changed the plugs and it is still doing the spark knocking. Im so confused right now, from a stop and flooring it through 1st-4th the car is fine. Only when I cruise in 5th or 4th gear with the rpms are low does it spark knock...

Im going to look into getting the MAF cleaner tomorrow and when I have to get gas Im going to try 89 or 93 octane fuel..

One of my friends said it could be a sticky valve but idk...

joshjwc9 · Jul 28, 2011

Next fill up throw some Premium fuel in the tank. It could very well be watered down (poor quality gas) or carbon buildup on the valves or the injectors getting gummed up.

Are there any present codes saved in the ECU you can read with your SCT handheld?

Is it a motorcraft fuel filter? Without codes, or recent work done to the car it is kind of hard to pinpoint over the internet. But, then it is related to the intake tract, fuel or the SCT tuner, IMO.

03_TrueBlue_GT · Jul 29, 2011

joshjwc9 said:
Next fill up throw some Premium fuel in the tank. It could very well be watered down (poor quality gas) or carbon buildup on the valves or the injectors getting gummed up.

Are there any present codes saved in the ECU you can read with your SCT handheld?

Is it a motorcraft fuel filter? Without codes, or recent work done to the car it is kind of hard to pinpoint over the internet. But, then it is related to the intake tract, fuel or the SCT tuner, IMO.

Yes I did buy a motorcraft fuel filter and no the car hasnt had any CELs come on since this has started happening. Perhaps the 100* weather and the ethanol mixed gas is causing it to do this but thats all I can think of right now besides cleaning the MAF.

BTW thanks for the tips and help everyone I really appreciate it.

Lugnuts · Jul 29, 2011

Another thought - do you have a timing adjuster on the car?
There have been many great suggestions so far but my guess would be a bad tank of gas if it has only been acting up for a short time (when you try the 93 octane make sure you are getting a tank full not just diluting suspect bad gas with a little new higher octane). How long has it been knocking?
For spark knock, the usual suspects are too low octane, lean mixture, wrong heat range plugs, timing off for rpm range where occurring, and hot spots due to high engine temp or build up.
Sounds like you are getting spark fine but has it knocked for the 30 to 32K miles you have had those plugs? I would inspect them regardless.
Check fuel pressure and injectors - a low pulse signal at part throttle with a bad spray pattern injector can cause problems. remember the 3/2s rule - too lean, too long, too bad.
Check your cooling system as well. With the car cold, does it knock right off the bat or just after it gets up to temperature?
I know this is alot to check but it is worth it.

03_TrueBlue_GT · Aug 9, 2011

Update

I put a full tank of 93 gas through it and the car isnt spark knocking anymore. I think it was the fuel that was causing it and I also cleaned the MAF sensor. I think the plugs also were a problem bc they were burning to hot for the engine compared to the OEM plugs I have in it right now.

Thanks for the help guys I thought I would just let you know that I have it fixed now.

I can post up pics of the plugs when I get off of work if y'all wish to see them.

trombonedemon · Aug 9, 2011

03_TrueBlue_GT said:
Update

I put a full tank of 93 gas through it and the car isnt spark knocking anymore. I think it was the fuel that was causing it and I also cleaned the MAF sensor. I think the plugs also were a problem bc they were burning to hot for the engine compared to the OEM plugs I have in it right now.

Thanks for the help guys I thought I would just let you know that I have it fixed now.

I can post up pics of the plugs when I get off of work if y'all wish to see them.

Thanks for posting back, thats very rare these days, people get help and then we never hear from them again.

trinity_gt · Aug 10, 2011

Hmm. A stock (or near-stock) PI 2V should be able to run 87 octane without the sort of detonation you described. I'm glad the higher octane fuel helped but it remains a bit of a mystery.

I see you're in Houston: You've had some pretty insane ambient air temps of late. I wonder if that's been playing a role...

Lugnuts · Aug 10, 2011

After the higher octane fuel is used, try the 87 again and let us know if it was just a bad tank of gas or if the problem is still there. I know a lot of people think all gas is equal but it is not - they each put different additives in. I like Hess when possible. Learned more about gas stations after a couple problems caused by them.
I had purchased a '68 SS camaro that was in good shape but had been sitting for some time. Drove it for a year before getting a tank of gas from BP. The extra detergents they put in there cleaned the inside of the fuel system well and clogged the heck out of a new fuel filter. Needed work anyway but was waiting for a "convenient" time.
I also had a '65 mustang and was out of town and got a tank that seemed like 50/50 gas/water... This station made the news - apparently they had problems with rainwater getting into the tanks for years and did nothing about it until a bunch of cars (including mine) filled up after a big storm and all died about a mile or less from the station.

03_TrueBlue_GT · Aug 11, 2011

trinity_gt said:
Hmm. A stock (or near-stock) PI 2V should be able to run 87 octane without the sort of detonation you described. I'm glad the higher octane fuel helped but it remains a bit of a mystery.

I see you're in Houston: You've had some pretty insane ambient air temps of late. I wonder if that's been playing a role...

It is very hot down here thats for sure, I am ready for winter, or our mild summer as we like to call it down here lol.
I do remember going to a Kroger grocery store to get gas when I filled up with 87 octane fuel so that may have been the issue, guess thats what happens when I shop for the cheapest gas.

One strange thing I have noticed though with Shell Gas is that I get worse mpgs, I guess its all the cleaning agents they put in the gas. I only use Chevron or Exxon gas now after I have been having issues with the car...

Lugnuts

After the higher octane fuel is used, try the 87 again and let us know if it was just a bad tank of gas or if the problem is still there. I know a lot of people think all gas is equal but it is not - they each put different additives in. I like Hess when possible. Learned more about gas stations after a couple problems caused by them.
I had purchased a '68 SS camaro that was in good shape but had been sitting for some time. Drove it for a year before getting a tank of gas from BP. The extra detergents they put in there cleaned the inside of the fuel system well and clogged the heck out of a new fuel filter. Needed work anyway but was waiting for a "convenient" time.
I also had a '65 mustang and was out of town and got a tank that seemed like 50/50 gas/water... This station made the news - apparently they had problems with rainwater getting into the tanks for years and did nothing about it until a bunch of cars (including mine) filled up after a big storm and all died about a mile or less from the station.

Yes I will use 87 the next fill up, frankly Im not enjoying the 50+ price for a full tank of 93 gas every week and a half, but I do enjoy having the Tune on 93...

Trombonedemon

Thanks for posting back, thats very rare these days, people get help and then we never hear from them again.

No problem I plan on staying on this site for a while, there are a lot of helpful and knowledgable members here. Plus I want to learn and be able to help other Mustang guys.

1987stangman · Aug 12, 2011

I could be totally way off here since I'm used to my 96's engine controls and sensors, but I know my 04' PI motor I put in my 96' (which I removed as the 96' PCM does not use one) had a knock sensor in valley under the intake manifold. Any chance it could be bad causing this issue with lower octane fuels? The car really should (in stock form with no tune) run fine with 87' but if higher octane fuels clear it up there is something else causing the issue unless he got a really, really bad gas fill up.

trombonedemon · Aug 12, 2011

1987stangman said:
I could be totally way off here since I'm used to my 96's engine controls and sensors, but I know my 04' PI motor I put in my 96' (which I removed as the 96' PCM does not use one) had a knock sensor in valley under the intake manifold. Any chance it could be bad causing this issue with lower octane fuels? The car really should (in stock form with no tune) run fine with 87' but if higher octane fuels clear it up there is something else causing the issue unless he got a really, really bad gas fill up.

Thats interesting my Haynes manual says that only the Dual Overhead Cammed engines have the knock sensor.

03_TrueBlue_GT · Aug 13, 2011

trombonedemon said:
Thats interesting my Haynes manual says that only the Dual Overhead Cammed engines have the knock sensor.

My Chiltons manual says the same thing...

trinity_gt · Aug 14, 2011

1987stangman said:
I could be totally way off here since I'm used to my 96's engine controls and sensors, but I know my 04' PI motor I put in my 96' (which I removed as the 96' PCM does not use one) had a knock sensor in valley under the intake manifold. ...

You sure that's not a CHT (cylinder head temperature) sensor? Truck 4.6s came with one; was the NPI engine the original or had it come from a truck?

2002BLGT · Aug 14, 2011

Did you select the 87 octane strategy tune ?

2003 GT spark knocks bad

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