i had my car dynoed for the very first time yesterday. from what i can see on the graph there is somethin seriously wrong with it and i dont know what to do or how to fix it. i dont have much experience with dyno graphs but i'm pretty sure the hp curve isn't supposed to start dying at 3200! also it looks like my a/f ratio is very rich at higher RPMs. i had my pressure set at 50 so last night i went to the track and lowered it to about 42. car ran worse by a tenth. i've ran it now several times and i can't seem to get anything lower than 14.8 with 92mph traps and 2.1 60's. i tried setting the FP even lower but the car started to run worse. so i bumped it up again. i dont know if the fact i'm running rich has anything to do with the early loss of power, or if there is something wrong with the motor itself. there is a sticker on the block that says "remanufactured", and since i dont have any history on the car im thinking maybe it has a cam that doesn't belong on this motor.

the torque is definitely noticeable. last night i took a late 70s trans am off the line by like 4 cars, but he eventually caught up and got a 14.6 to my 14.9! i have no top end!

i'd like to hear some suggestions cuz i'm seriously thinking of not wasting my money anymore and just save up for another motor or another car. motor and tranny seem to be strong and i try to keep this car in top shape. mods are in my sig. thanks.

 

red arrow - peak tq

black arrow - peak hp

 

[Captain Obvious] Say, your running a little rich there. [/Captain Obvious]

 

anyone else????

 

Sorry, just being my wiseass self.

You didn't pull the fuel pressure back while on the dyno?

(edit) Isn't stock pressure 45?

 

i had the stock regulator in when it was dynoed, i just did the quarter trick to raise the FP. before i went to the track i put in the adjustable one at about 42 psi. one guy at the dyno shop said 5 psi drop should be enough to get the a/f ratio to the right level. i know i dropped 8 but doubt 3 psi woulda made a big difference. it's just running way too rich and i dunno if this is why the motor is dying so early.

 

I see....

I personally wouldn't bother messing with the fuel pressure without a strip/dyno for testing. Too much of a guessing game.

 

im thinking your on the right track when you say the cam might be your problem. it might not be computer compatible. when i had my motor rebuilt in my gta they put a cam in it that would pull real hard on bottom end but after 3300 it would just stop pulling and run rich. it may or may not be your problem but it was mine......just my 2 cents worth...........

 

Whats up dude.

 

FYI: According to your graph your HP peak is at 3900 RPMs not 3200. Your torque is what is dropping off after 3200 RPMs. Are yuo disconnecting and plugging the vacuum line when setting the fuel pressure?

 

isn't it the opposite?? the black arrow points to the highest peak of that curve which is almost 300, so that would be torque. the highest peak of the line with the red arrow is almost at 200 so that's hp. the hp line starts to go down around 3200. i mean thats how i see it.

yeah im setting the FP with the vacuum line disconnected and plugged.

 

yo

 

you runnin the stock prom? that is prob the prob.

 

I doubt that.

So there's no way to contact the previous owner or anything like that so maybe you can find out what kind of cam is in there?

 

As for the dyno sheet:

Isnt the black arrow pointing to HP?

Because it wouldnt make much sense if the car was making more Torque than Horsepower at the higher RPM's.

 

you guys are right. i looked at it again and realized i hadn't lined up the peaks with the #'s on the side correctly. but i still have a problem. TQ and HP are still dying too early and am running extremely rich. i should have a steady rising line until about 4800 and maybe even more with the ported plenum and runners.

yea im runing the stock prom. but i doubt it needs to be reprogrammed already with the basic bolt ons i have.

as for contacting the previous owner. i was thinkin of going to the dealer where i bought it from and trying to find out. it's probably been too long though (2 years since i bought the car).

sorry for the mistake

 

I completely agree that you should definatly be making more power - either way those curves shouldnt be dropping like that. Give the dealership thing a shot!

 

from what i can see, the afr drops below 11.0 to 1 at 3400 rpms. i would say that you do need to burn a prom to fix your prob. need to play with the timing and fuel to get the afr correct the rest of the way through the rpms. that is what i think the easiest way to fix your prob would be.

 

i would put a vaccum guage on their and see what it pulls that would help detect traces of a larger cam , an since SD cars live off manifold press. a drop in vacc. would run the way rich, MAF can get away to an extent but you really cant fool the MAP sensor , whats going to tough is when get the chip theyre gonna want to know what cam you have , also it doesnt hurt to check the timing that can really make difference.
good hunting young anakin :lala:

 

hot damn em arh some fanC tipeing ckills i gots

 

I agree totally.....My bolt on L98 would only put out 192 RWHP, I noticed the pinging, Decreased timing and picked up another 15 horses(RW that is)

Timing is EVERYTHING!!!!!!

Later

 

cam cam cam :hail: ---->305 tpi

 

if u were at 50 psi fuel pressure on the dyno and u are WAYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY RICH, decreasing it should help, BUT u cant go down 8psi of pressure and expect it to help. thats way to much of a decrease, start at 48, then 46, then 44. oh yes and timing is very very important with all this. try 8-10* advance, i run 12, my car runs best there.

 

i agree, decreasing FP should help, but should it really change the a/f curve that much? mine is literally off the chart it's so rich. i have the timing only a couple of degrees advanced from stock (8*). my friend's 85 LB9's (almost same mods as me) a/f ratio line is a lot closer to where it should be on the graph, with 50 psi of FP.

i wouldn't be surprised if i do have a bad cam in there. i remember even with stock FP regulator and before i did any mods, the car just never felt like it had any power up top.

 

1) You need some serious pump-shot (acceleration enrichment) because you are lean when the throttle is stabbed. Increase the values in the AE vs. Delta %TPS table in the PROM.
2) You are rediculously rich across the board. Change the PE vs. Coolant table by decreasing by ~18%. This corresponds to about a 2.0 AFR change.
3) Use the PE vs. RPM table to smooth out that AFR graph.

Here's an example of what I was able to do via this type of tuning ...

http://www.celligent.com/tim/iroc/dyno/dyno_afr.jpg

Tim

 

thanks for the suggestions but prom turning is something i haven't gotten into yet. even if what you're saying will lean the mixture up more, is this really necessary with the simple mods i have? engine's almost all stock. why would it need so much tuning already? just wondering...

i know i'll need to eventually learn about this stuff. i dont plan on keeping this car in the pathetic high 14's area.

 

now i really dont know what to do. i'm thinkin it could be a bad cam, but what if someone already installed a better than stock cam, but just didn't reprogram the prom.

also, could bad injectors be causing this???

i seriously feel like yankin the damn motor out of this car and tossing it in the nearest lake

 

i measured engine vacuum. idle reads about 20. when slowly giving it gas, it goes up slightly. this normal?

 

20 for vacuum at idle is right where you are supposed to be for a stock/almost stock cam. Under accelleration you should loose vaccuum, not gain it. Once your rpm's level out so will your vaccuum #'s.

I'm definately interested in seeing what is making you so rich. Keep us updated

Matt

 

Check your exhaust system - things that will make a basically stock set up run so rich (aside from the fuel at 50psi) is bad cat,,, flattened "Y-pipe", or crimped exhaust pipes.

I'd also check the lifter adjustment and set it between 1/4 and 1/2 turn - unless you set them yourself - no telling where they're set.

 

the vacuum will drop then rise if you are doing this in park and part throttle. it should drop and stay at 0 if you are doing a WOT run.

 

everything in the exhaust should be good. dont have cats and no crimps on the pipes.

 

Take that piece of **** 160 degree thermostat out and put the 195 degree stat back in. The computer is reading that your engine is still running in cold start up, therefore its just dumping more fuel in there then needed. Its trying to warm the engine up with a rich fuel mixture.

 

What size injs are you using?
Sounds like maybe the ECM thinks they are smaller than they really are.

Could also be the ECM coolant temp sensor. It may be telling the ECM that the eng is colder than it really is.
Either interface with the ECM via laptop and check the reported temp or you can check the sensors resistance using an ohm meter and the temp/resistance look-up chart below (which I copied from one of Vaders posts).

BTW, I would run at least a 180* thermostat in any eng. Especially a computer controlled eng.

 

i'll check on the CTS and the MAP. AFAIK the injectors are stock 22#'ers. but i'd have to verify. i think LT1 injectors look the same but have higher flow, which would be causing a power loss if the ECM hasn't been reprogrammed.

i put in a 180* stat last night, and cleaned up my air filter a bit. went to the track but unfortunately wont know if it made any difference. only got to run once for 1/8 mile, and the launch was terrible.

 

The 160 thermostat isn't the cause of any of your problems. Everyone of us one here runs one, including me, and I have my fan running all the time.

Turn your fuel pressure down, the factory tune is already rich enough.

Do you have access to a scanner or data logger? That's what you need to adjust the air/fuel.

 

Are you throwing any codes? It almost sounds like your knock sensor is picking up massive amounts of knock, which is causing the ECM to over compensate with fuel. First things first... get under the car with an ohm meter, and test that knock sensor. It should read 3.9k ohms. If it doesent read that, then theres your starting point.

 

well i think i finally found my problem. the # on the heads that are in my car read 14102191 which according to different posts on here, are not stock heads and happen to be TRUCK HEADS!!!

i remember i checked the # a long time ago but all it said was 350 so i left it at that. never ocurred to me back then that a 350 isn't necessarily an L98.

now i know why that dumbass mechanic charged so cheap for a head replacement 2 years ago. i wish i had known back then what i know now. but of course that was before i even joined this site.

now on to look for new heads!!!!

 

hahaha

 

Glad to see you found your problem. Bet you didn't see that coming

 

i guess i shouldn't give up just yet