Dyno results...Input needed!

**Azchan63** · 10-14-2014, 09:31 AM

Scan.jpg

Just did 3 pulls on a dyno and the pic is the best pull (296HP/318TQ). Kinda disappointed b/c I was expecting 300+ HP and TQ.
It is a 98 Z28 M6, mods are: lid, SLP LM2, and p&p tb. They did say the car is running lean (AFR = 16.38) what could be the problem(no check engine light)? I also notice that there was a big pop after the guy let off the gas during the dyno run...should I be worried? It might just be the LM2 being loud and poppy but I just want to make sure b/c it didn't sound normal. Btw I just cleaned the MAF a couple days ago but I will clean it again just to make sure.

I just bought the car a couple months ago with 75k miles for $3,500. The previous owner basically garaged it and never drove it. All I've done is oil change and brakes/rotors, is there anything basic maintenance wise that would cause the car to run lean? Maybe front o2 sensors? Oh and is it ok to drive a car that lean? I'm thinking about getting a tune once I get my LT headers.

Thanks for you input!

**98TransAmWs-6** · 10-14-2014, 11:01 AM

That sounds about right especially since you don't have headers. I would definitely suggest a tune after headers to get the most out of your upgrades.

***SMWS6TA*** · 10-14-2014, 11:32 AM

With some basic mods and a tune up you should be able to wake up your car.

Give your car a tune up - new filters (air & fuel), plug change (NGK TR55's are highly recommended for LS1's), Clean the MAF (w/MAF cleaner) and use 93 Octane gas. Lower than 91 and you'll have knocking issues.

Now for the basic mod list.

1) Headers, headers, headers, Long tube is best, it will open up the choke hold on the LS1, combine it with an ORY. Did I mention headers?
2) LS6 intake - they can be had for around $300-$400. It provides IIRC 20% more air volume over the LS1. For 80% of ppl's needs/builds the LS6 is perfect. Now if you're making a track pounder then there are other intakes that fit those builds.
3) DELETED the EGR & air pump. - we have a couple of help threads on this subject. These systems are not needed and GM removed them off of later yrs.
4) After you get the above completed, send you ecm to Frost and have him do one of his tunes. Best mail order tune you can get.

Do this and you should add 25-40 hp when said and done.

I have to warn you once the mod bug bites it's hard to resist stopping there.

**Firebirdjones** · 10-14-2014, 12:37 PM

Considering the differences between dyno's, those numbers look pretty normal.

Seems odd to me though that the graph shows the engine falling off past 5300 and is rather jaggy after that. Almost as if it's either running out of fuel/detonation or valve springs.

Since you were running CRAZY lean at 16+ AFR (and I'm surprised they continued the pull with those AFR numbers, I would have shut it down) I'd bet you have a weak fuel pump. That lean condition up top could definately cause detonation which might explain the jaggyness above 5300 as well.

With that stock tune that thing will command about an ~11.7 AFR at WOT. If you were really seeing 16+ I'd guess a fuel delivery issue. I'd get a fuel pressure gauge on there and verify. At WOT in high gear you should see a steady 58 psi.

**theorangeguy** · 10-14-2014, 12:44 PM

Step 1...

Long tube headers. It will wake the car up quite a bit.

**Azchan63** · 10-14-2014, 01:29 PM

Thanks all who gave me feedback, I'm gonna check the fuel pressure. Also I notice that it smelled like something was burning when my car was dyno-ing. It's the smell after my exhaust got welded...but I got that done couple weeks ago. Does that help anyone with enough info to diagnose my high afr? Once again, thanks for all the help

**pajeff02** · 10-15-2014, 07:30 AM

I agree with what FBJ posted. That is way too lean. Check pressure at the rail as you want 58 psi. Even under load it should be close to this number, but may drop a bit. Has the fuel filter been changed lately?

***SMWS6TA*** · 10-15-2014, 08:11 AM

Could injectors be an issue?

**Azchan63** · 10-15-2014, 08:26 AM

I haven't changed it since I got the car...and I'm not sure if the previous owner did. I'm gonna try to change the filter and test the fuel pressure today to see if that's the problem.
EDIT: Got in contact with the previous owner...said he hasn't changed it in "a couple of years"...

**pajeff02** · 10-15-2014, 09:27 AM

Hope it is a simple fix.

**35th-ANV-SS** · 10-18-2014, 09:24 AM

Let us know what you find with your fuel pressure. You do not want to continue driving the car with it being lean. That could lead to other problems that you do not want to deal with.

**Azchan63** · 10-19-2014, 01:55 PM

Ok I changed the fuel filter, it was VERY dirty (all black inside), and checked the fuel pressure. It was kind've weird, with the key in and turned to the "on" position it started at like 50 psi and dropped to around 40psi. Then when i started the car the psi jumped to 57-60ish psi. I also rev-ed the engine to see if the fuel pressure dropped but it did not. Is there a easy way to recheck the AFR to see if that fixed the problem?

**35th-ANV-SS** · 10-19-2014, 02:12 PM

Dropping pressure with the key to just the "on" position without the car running is normal. Don't see anything too alarming with those results, although I'm not sure how much pressure should drop to. It's good you're getting normal fuel pressure with the car running and at WOT though.

You didn't by chance check fuel pressure before changing out the fuel filter did you? That would have told you if changing it helped.

**Azchan63** · 10-19-2014, 02:37 PM

I completely forgot to do that, I realized it after changing the filter out

How would I check my AFR again without paying 60$ for dynoing?
And if its not the fuel related, what else could it be? Front o2 sensors?

**35th-ANV-SS** · 10-20-2014, 02:37 PM

You could always put the old one back in

Does the car run better now?

**pajeff02** · 10-20-2014, 05:45 PM

You need a wideband O2 gauge and sensor to monitor AFR. The output on the stock sensors is "narrowband" and rapidly cycles up and down such that it is essentially worthless as a tuning tool.

**Firebirdjones** · 10-21-2014, 07:07 AM

I would have prefered to test the fuel pressure first before making any changes at all. Simply reving the engine while sitting still won't show any fuel pressure issues.

You still need to test the fuel pressure as I stated in my last sentence in post #4. You need a high load, high gear full throttle pull to see if the fuel pump is keeping up under those loads. A fuel delivery issue will always show it'self in those conditions. Just as I believe it did on your dyno run. Would prefer a wideband on the car as well to verify the lean condition is still there.

If fuel pressure drops off, then you'll know the fuel filter didn't fix it. If fuel pressure is steady at 58psi under these conditions, well then 1 of 2 things happened. Either the filter fixed it (which we won't know for sure because you didn't run this test before hand) or the fuel pump isn't the issue and we still don't know if you have a lean condition unless you have a wideband on there to verify.

Best case scenario the filter fixed it, but you'll need a WOT run with fuel pressure and AFR monitored to know for sure.

Edit: Frankly it would be ALOT cheaper for you to hit the dyno again (not to mention safer) If they only charge $60 for a pull. A good wideband setup, even a cheap one is at least $200 (unless you know someone that has one for you to use). And a universal fuel pressure gauge with a line made long enough to reach the windshield where you can duct tape it for a drive (is what I do) might be another $50-$60 for a cheap setup. I actually use a an old R12 freon hose and gauge with about 4 feet of hose just for this purpose. It's the perfect size to screw right onto the schrader valve.