Embarrassing low dyno numbers and need some help

**Trooper182** · 09-11-2016, 08:11 PM

Ok so today got to do some pulls at a local shop and the numbers are crap. The car is a 04 gto auto. I bought it about a month ago. It just had a new (used) motor put in it. It also has a cam, pacesetter LTs, cats removed, heads done. All work was done before I bought the car. The car itself has 114k miles on it. We just got done working some issues with it and had it on the dyno and it made....embarrassing 263hp on first pull. After some changes to the tune it maxed out at 275hp. So obviously something is not right. The car starts up and drives fine. Accelerates good but you can tell it is not operating at its max performance. I think my old 2011 v6 camaro pulled harder. So I need some ideas, things to check. I could pay the shop to figure it out but I like learning and want to exhaust everything I can do on my level before I have to bust out the wallet.

**Naaman** · 09-11-2016, 10:10 PM

Ugh....

Anyway to verify the internals? Receipts? Build sheet? What engine is in it? I'm presuming an LS1... those numbers look like stock numbers, more or less.

Some other questions that may or may not be relevant: What altitude are you at? Aftermarket wheels/tires? Are you sure the car was set up correctly on the dyno (wheels centered on the roller, etc)? How's the torque converter? Is it locking up correctly? Are there any codes in the history?

I'll tell you something that happened with my car:

I got under the hood to do a spark plug change and found that two of my plug wires were fried and completely severed. So I was running on 6 cylinders. You would not have known it from how the car ran, other than the popping exhaust off-throttle. No smoke out of the tail pipes, no smell, no codes... nothing. After installing fresh wires, the car accelerated with much more authority, but a lack of power (as measured on the butt dyno) was the only symptom.

**Trooper182** · 09-12-2016, 02:40 AM

The motor is a ls1 and was installed at a local shop before the dealer got the car. Im located in central texas so alt is not that high. Stock rims and yes the car was centered on the rollers. As far as I know the torque converter is good and no codes in history. I never thought to check the wires. I did do a spark plug change yesterday and did not see any evidence of bad wires (wires are msd.) Could this possibly be a fuel issue? Weak fuel pump?

***SMWS6TA*** · 09-12-2016, 04:03 AM

How high was the dyno pull? up to how much rpm?

Any codes showing?

The tuner can see if any CEL codes are turned off?

Lean or running rich, again the tuner can see this looking at the data. For you look at the plugs, white = lean, soak or black = rich, oiled up = bad rings.

Does the dealership or shop know why the previous motor was replaced?

Try doing a Compression Check, not hard to do but will give you a good indicator of the engine and what to do next.

***SMWS6TA*** · 09-12-2016, 04:08 AM

on a side note, is the dyno shop good? Ive seen, no joke, a local shop tell my buddy that his 383 Stroker only put down 325 to the wheels when the month before I saw it put down 475 at 75% open throttle. We went and fixed the gas pedle to open 100% and instead of driving 3hrs to our tuner he tried a new shop that was doing dyno pulls. Turns out the guy is new to tuning and only went up to 5000 rpm. At 100% open throttle it goes to 495 to the wheels.

**Naaman** · 09-12-2016, 04:25 AM

Not to mention that dynos are a "guideline."

**Trooper182** · 09-12-2016, 04:35 AM

I want to say the pull was done up to 5500rpm. No codes showing or turned off. The car was running rich so he made some changes and was able to get 275.

**Trooper182** · 09-12-2016, 04:37 AM

The shop i took it to was the second shop to dyno it. First shop showed the same numbers so i wanted to get a second opinion to see if the numbers stayed the same.

**Trooper182** · 09-12-2016, 04:53 AM

I think i may have found the issue. I think the number 8 cyl is dead. I tried poring water on the heder tubes after letting it run for about 20 sec and all of them instantly steamed except for 8. Water just rolled off of it. Pulled the plug from the coil and no change to how it ran although i could visibly see a spark from the coil. Guessing i need to do a compression test next.

***SMWS6TA*** · 09-12-2016, 05:59 AM

Originally Posted by Trooper182

I think i may have found the issue. I think the number 8 cyl is dead. I tried poring water on the heder tubes after letting it run for about 20 sec and all of them instantly steamed except for 8. Water just rolled off of it. Pulled the plug from the coil and no change to how it ran although i could visibly see a spark from the coil. Guessing i need to do a compression test next.

This is why I invested in one of those laser temp readers (Harbor Freight $15).

Yeah that will kill all power. Before you do a compression check, try swapping the plug to #6 cyl and see if it follows the plug, if not, next move the plug wire, if it still hasn't moved lastly swap the coil pack. If it still stays on #8 then do the compression check.

Any white or black smoke from the exhaust?

**Trooper182** · 09-12-2016, 06:23 AM

I have an infrared temp gauge at the house that Im going to try when i get off. Another thing i noticed is the headers all look a little darker compared to the 8 cylinder. I tried disconnecting another cylinder and ran the car but it seemed like it did not change anything. Ill have to do more tests when I get home. No blue or black smoke is coming out of the exhaust. Out of curiosity what compression numbers should I see? Also what fuel pressure?

***SMWS6TA*** · 09-12-2016, 06:49 AM

Fuel Pressure at the rail should be around 56psi.

That could also be an issue, #8 injector clogged or not working. Check it to see if the harness is connected. You wouldn't be the 1st person to forget to have it hooked up

CR for LS1 I can't remember, should be in the 100's. Important number is that all of the cyl are within 10-15 psi. 0 is very bad. If more than 15 psi make sure the connector is fully seated. Some cyl are a royal PITA to seat it like #8.

Look for numbers that are way off. Don't start with #8 right away. Do one head at a time also. Post numbers.

**Trooper182** · 09-12-2016, 06:59 AM

Ok ill also check to see if the injector is clogged

***SMWS6TA*** · 09-12-2016, 07:48 AM

You can swap it to another cyl as well to see if it follows.

**Trooper182** · 09-12-2016, 07:50 AM

Good deal. Looks like I have a few test to do when I get home. Ill report my findings

**Trooper182** · 09-12-2016, 11:17 AM

Little update. I took an early lunch and did some testing. It turns out the #8 is firing so that is not the issue. I did a fuel pressure test and with the engine off the pressure was at 52psi. With the engine running at idle it jumped to 60 psi. So still no idea why i am down on power. Will try a compression test when i get home. Out of curiosity I dug a little deeper into my scan tool and found that the first tuner turned off the light for a code. The code i p0342. The thing us when I first brought him the car it was throwing code p0343 and I thought we had rectified this issue. As I understand it if the camshaft position sensor was not working i would have very hard starting and drivability issues, none that im having other than the car not producing what it should be.

**Trooper182** · 09-12-2016, 05:22 PM

Ok so I did a compression test on all the cylinders. Disconnected the the ignition and disabled the fuel pump. Held the throttle wide open and this was the results. #1=90psi, 2=93ps1, 3=95psi, 4=90psi, 5=90psi, 6=90psi, 7=90psi, 8=94psi. So I know it should not read below 100psi. The question is what could be causing these low numbers?

**Naaman** · 09-12-2016, 09:05 PM

Is it supposed to be done with the throttle wide open?

**Trooper182** · 09-13-2016, 02:46 AM

Yes per the service manual it says to do it with tje trottle held wide open while cranking the motor 4 revolutions

***SMWS6TA*** · 09-13-2016, 06:59 AM

Ok I looked at my manuals last night and the compression should not be below 100 psi with TB open. They are within the average so nothing stands out so far.

Now you said you confirm that the #8 is getting spark? How did you check?

If the compression is good, meaning it holds pressure and is letting air move in and out of the cyl (valves are good) and getting spark that just leaves fuel. Easiest way to check would be to move the injector to another cyl and see if it follows. If it does the injector is the issue, if it doesn't then you need to look at the harness very good.

Being down a cyl could be popping your cam code because it's effecting how the car starts which will trip up the code.

Here is from the manual:

Engine Compression Test

Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Block the throttle plate wide open.
Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
Make the compression check for each cylinder. Record the reading.
If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
Recheck the compression and record the reading.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking -- Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.