I thought I had my car all back to running 100%, but I guess I didn't...or else a new issue has surfaced.

Drove about 55 miles to the DynoJet facility, and I noticed when I stopped at a toll plaza that car was surging, and I also noticed that car seemed to be a good bit down on power when pulling away from toll booth.

Anyway, my car was cooled down to 160* or so before first dyno pull. I made 6 pulls in all before throwing in the towel and calling it quits. The runs were measured from 2400-5000 rpm's. All runs were nearly identical, and numbers were UNcorrected for whatever reason.

Anyway, first pull was best pull, and very disappointing to say the least. Base timing was 6*, base fuel pressure 38psi.

239.53 rwhp @ 4400 rpm's
359.06 rwtq @ 3100 rpm's
Avg. HP from 2400-5000 was 217.05
Avg. TQ from 2400-5000 was 314.85...329.06rwtq @ 2400

A/F ratio was low 13:1's up until 3300 rpm's, then it popped and backfired (misfired) steadily from 3300-3900 rpm's, then it would clear up mostly and A/F would go lean at low 14:1's up until 5000 rpm's. It did this every pull regardless of base timing or base fuel pressure. No idea WTF is going on with car now, but it's way down on power when under load at WOT, the car breaks up badly and acts like it's got a dead cylinder. In fact, all around power is down for some unknown reason.

The only plus side is that I found out my HP, even though it is down, doesn't drop off like the typical TPI engine does. It was at 230 at 3900 rpm's, and 231 at 5000 rpm's, so whatever is wrong right now is holding it back from what I see on dyno sheets...Basically when a/f goes bonkers and the car misfires/backfires, the hp stays pretty much right where it is until I let off the gas pedal.

No idea where to go from this point, but I do know I'm getting disgusted with all the issues since the head.header, and intake swap...

Spark plugs are new, gapped at .040"
Plug wires are new
Distributor cap & rotor are new
Valves are adjusted down 1/2 turn past zero lash
TPS is set at .540v at idle
Base timing is 6 degrees
Base fuel pressure is 39psi

The other day the car was running absolutely fantastic, and truly felt like a car that was making 25-50 more hp that it showed...today, it's just running OK unless at WOT, then it is breaking up/misfiring/whatever you care to call it...

BTW, recent mods are:
New Summit 170 heads
Crane 1.6 roller rocker
Hedman Longtube headers
2-1/2" Y pipe
Ported Edelbrock base
Ported/Siamesed SLP runners and plenum
Adjustable fuel pressure regulator

Any thoughts or ideas are appreciated...

You can see both HP and TQ were still climbing until it gets whacky at 3300 rpm's. Pretty clear in all 5 dyno pulls, at 3300 it does whatever it's doing, which totally screws up the graphs and a/f ratio from that point on...

 

Needs more Camshaft..........

 

I didn't see fuel pressure addressed in your list. Maybe an old fuel pump? Fuel filter need replacing? How is the voltage at the pump? No electrical losses along the way?

Scot

 

Fuel filter is only about 1000 miles old, but I didn't have the ability to monitor fuel pressure during the pulls, unfortunately.


Thanks for the reply, but we all know "more camshaft" isn't going to fix an issue that happens at 3500 rpm's...

 

I think you should bring it to the track an see what it runs. I some people get crappy Dyno #'s but run pretty good 1/4 mile times

 

Is your AFPR a Holley? Mine just tore the diaphragm at only 2,000 miles use. That will really mess with your power, believe me....

 

Change your spark plug gap to .035, my vette will misfire at WOT if I run more then .035 in plug gap. This may not be the problem but it is easy to change and could solve your problem.

Also check the coil in your cap and make sur the ground wire is tight, mine loosened up and would miss at high RPM until I tracked the loose conection down.

 

I got 251rwhp/318 rwtq untuned with my setup in my sig ( minus turbo ) I got a graph if you wanted to see it. My SLP 1.75 headers hurt my TQ a bit I think

 

Look I'm not trying to be a A-hole. Aren't you guy who spent money on everything only to run the stock camshaft? If so I stand by my statement. A stock car with a ZZ4 camshaft would accomplish more than you have so far.

 

I am looking at purchasing a set of SLP headers. With a Borla system on the back.I thought the SLP were suppose to be a good set up. Did I miss something in my readings? Thanks for any info

 

I wouldnt worry too much about the numbers, just that the car isnt running right. Fix that, whatever it may be. Just from my past experience and what you're saying, sounds like an ignition issue of some sort. Check grounds, check for good spark, check the plug gap, etc etc.

If you want to venture a guess what it would do HP wise with it running right, make a trendline up to about 44-4800 (somewhere in there) and see what its at there. Probably 260-270ish, with about 10-20ft/lb of tq more than you have.

 

what dyno shop did you go to i saw that your from baltimore im up in harford county and trying to find a place to dyno tune my formula, thanks

 

At 3500 you are going way to lean. Correct your fueling issue. You are either losing fuel pressure, your inj's are to small or you need to retune your chip. Get a fuel pressure gauge on it and check the pressure at WOT. You are leaving a lot of HP on the table running that lean.

 

Heck...A well running stocker (TPI Vette) with a stock cam can match what mine's doing right now...lol.

My point in my original reply to you was, and still is, that my thread topic/dyno problems have absolutely zero to do with my camshaft choice. The dynographs very clearly show both horsepower and torque still heading upwards when the car popped, misfired, backfired, and whatver the heck else it was doing that caused it to suddenly lean out. I'm confident that when the issue at hand is figured out, the car will easily make 275rwhp/375rwtq, which I think is pretty stout for any car that's using 20+ year old technology, a simple combo of parts, and a stock flat tappet camshaft.

Not trying (or wanting) to be argumentive...just looking for ideas on what to look for with the problem I suddenly have. Let me, or better yet, help me get the car running 100%, then feel free to critique my choice of parts.

madmax's reply sums it up well. I'm not concerned with numbers right now, as they obviously are skewed due to problems I have yet to figure out. I need to "fix" the problems before even thinking about trying to tune it.

Thanks.

 

Funny you mention IGNITION....

Yesterday, I drove the car around with a mechanical FP gauge under the wiper blade...at WOT when it spits ad sputters, FP does not fluctuate at all. This tells me fuel pump, fuel filter were good. I had some new 24# injectors for the car anyway, so I installed them today. Car started up and idled better than ever before, so I thought I had found the issue. (stock injectors ticked like crazy, and all of their ohm readings were scattered)

Driving normal, car ran great, smooth as silk. First time I got on it, the car popped, backfired, gurgles, etc...then DIED....

I was able to drift to my buddy's house and when we checked, it was not getting any spark. I was getting ready to pull distributor and on a whim, disconnected TACH lead....car fired right up. I guess it's shorted out somewhere/somehow?

I also noticed on the way back home, car was "maybe" half as loud as it usually is...and I smelled rotten eggs....even though catalytic converter is less than 1500 miles old, it seems to be clogged, at least partially.

Tomorrow I plan to gut the converter, since I had planned to install true duals anyway, and see if that finally cures sudden power loss....
----------
ACA Performance in Newark, DE. Their number is on the dyno sheet above....

$110 an hour with a/f, and unlimited pulls
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Fuel pressure doesn't fluctuate at all under WOT and when car stumbles, and misfires...

 

What size injectors did you replace with the #24 ones. If they were the stock ones, you are now getting to much fuel. When you change inj size you have to tell the ECM what the new size is or it will run rich . (hence the smell of rotten eggs)

 

what about the maf sensor?

 

The 85 Corvettes came with 24#ers stock. I just upgraded to newer ones, but same size....

I guess the car will definitely register LEAN if nothing's coming out of the tailpipes, lol...
Here's what I found today:



http://home.comcast.net/~rel3rd/wsb/media/373752/site1423.jpg
http://home.comcast.net/~rel3rd/wsb/media/373752/site1424.jpg
http://home.comcast.net/~rel3rd/wsb/media/373752/site1425.jpg
http://home.comcast.net/~rel3rd/wsb/media/373752/site1426.jpg

BTW, GUTTED the cat out, and car runs fine again. I guess I have a shorted TACH lead though since car won't start if it's plugged in. (Factory tach, fwiw)

 

wow, thats gross!

 

I concur. I've never had that happen to me in 28 years of driving.

 

cant wait to gut my cat.... factory 89 cat...i hope its got some cloggin so i pick up some power. lol

 

Severe Ignition misfire almost INSTANTLY sends the cat temperatures to 1800°F and more. I do this stuff for a living, hehe (no really, this week I'm calibrating misfire detection for EOBD, and find misifire thresholds for cat overheat).

Not many materials can withstand those temperatures for much time. It's a good idea to break in a new engine without a cat as well. And to debug new setups.

 

Still workin on the bugs....

I should have just gotten some spray or something, LOL.

 

i like when people say **** like this... YOU ARE TRYING TO BE AN *** HOLE!! don't be a *** hole and not say your not trying... its dumb.... and no a zz4 camshaft wouldn't do ****.... 215-225 max whp???? give or take? i love that your answer to his problem is "give it somemor' cam" the guy has the right setup just working some bugs out. and that isn't bad numbers for a car f*cking up on the dyno. especially a TPI car. BTW awesome tq numbers! bet ya that thing is a bastard off the line!

 

let us know what the dyno numbers are after the gutted cat! im sure it will make a huge difference

 

Well the way most garages around here work , If your car come with no cat from the factory we don't need one. Some years it was an option so if you find out it was an option we rip them out . Some day all that will change but till it does we take full advatage of the fine print in the laws .

 

Traction is definitely an issue now. I just bought some BFG Drag Radials already mounted on stock Corvette rims, so that should take care of that.

As for the first part of the reply...
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I surely will, although the car will have a pair of Dynomax Ultra Flo's on it. It's just way too loud with the muffler eliminators and nothing but clear pipe between them and the longtubes.

I'm hoping for next Monday....a week or so away. Wish me luck.

 

no problem!!

 

Well...here is what I found.

TACH signal wire was shorted to GROUND...intermittently.
This was my severe misfire issue.

Converter guts were melted and clogging the exhaust (getting worse and worse). This evidently was my LEAN issue.

Car appears to run fine now...pulls hard to 5000+, so I hope to get back on DynoJet in a week or so...We'll see what this stock cammed L98 can do....HOPEFULLY

Wish me luck.

 

don't ya love it!!! sweet action post up the results!

 

good job man! hope it really picks up the power now

oh and i gutted my cat yesterday... didnt look like yours at all but i gutted it anyway.... jeez does that make your exhaust system louder!!

 

Nominated for understatement of the year, LMAO!!!!

Don't know what else you are running for exhaust, but mine, right now, consists of Hedman Elite longtubes, 2-1/2" front Y pipe, gutted Cat, stock 2-1/4" rear Y and muffler eliminators...pretty much straight exhaust from front to back...Later this week, it'll have a new 2-1/2" rear Y pipe and the Ultra Flows on it...should still be loud, but not excruciatingly so...

 

i just got hooker shortie headers and y pipe. 3inches all the way back thru a chambered tube muffler, 20 inch long case. pretty straight thru and its very very deep and mean at low rpms and screams at high rpms. idle sounds like it has a mild cam in it now...that i like. makes the car sound meaner than it really is lol

 

Sadly, I can relate to that....

One day maybe mine will be as mean as it sounds...
Maybe after some JUICE is bolted on?