Need help!

[1320quick]

Ok guys, I need some ideas. Took my Nova out for the first time this year and it did not go well at all. I made a ton of changes over the off-season. (I know, bad idea but too late now.) This may get long so please bare with me. A bit about the car... All steel 3600lb stock suspension 71 Nova, 14.1:1 540bbc, T400, 8" 5500 converter, 9" with 3:90's. Also, I race at Bandimere where the elevation is over 5800ft. Changed the ingition from a MSD 6al, pro billit dist and blaster2 coil to a MSD 7530T prog digital 7, pro power hvc coil and crank trigger. Also went from a adj nitrous works plate to a cold fusion fogger with edelbrock progressive controller.

Got 4 passes in on Saturday. First pass was a motor only 1000ft shake down pass. Timing at 36 degrees and old fouled AR3932 plugs. It was a total loss as the timed rpm limit took max rpm to 2000 after 9 seconds. I got that figured out and fixed. Second pass, same fouled plugs, ran 10.81 128mph. About what I expected but the car almost felt weird going into 3rd gear. Almost like the rev limiter was on. I had max rpm set to 8000 and shifted at 6900 so that shouldn't have been it. Then I made two nitrous passes. Set the initial timing to 31 degrees, phased the rotor and put a new set of ngk R5671A-8's in. Had 30 nitrous jets and 26 fuel jets as recommended for a 250hp shot. Had the progressive box set to leave fairly soft. I was taking an additional 5 degrees out through the digital 7 box at nitrous activation. Car launched fairly soft, ran a slow 1.48 60' but seemed to pull fairly hard. Car ran 9.54 at 146, just .020 off it's quickest pass ever and 4+ mph faster. The issue with that pass was that the engine backfired when I shifted into 3rd gear and I don't know why. I shut car off in the lights and towed it back to check the plugs. I'm not a great plug reader by any means but they look pretty lean. Even the thread were white. I put a fresh set of same plugs in, up'ed the max rpm limit to 8300, set the shift rpm down 200rpm, set the dig7 to take only 4 degrees out and set the progressive controller way more aggressive. It left hard with the wheels 3 feet in the air, ran a 1.40 60' and a 3.844 330'. Seemed like it was on a great pass. When I shifted into second gear, engine backfired again 4 or 5 times and I shut it off. It was bad enough even my girlfriend noticed the flames coming out the exhaust! What gives here? Did upgrading the ignition system throw my motor only tuneup out of whack and now it's lean? 36 degrees and 92 square carb jets has always been perfect in the past for the motor. I checked to make sure that the dig7 was not taking out additional timing on shifts. Could this be a lean condition? Voltage problem? Just not sure where to go. Any ideas would be great!

[ytnova]

Hmmm, We just went through this this weekend, A girl down here has a blown alchol bmw that they just changed to the digital box on and it did the same thing, but at a lower rpm. You did use the new sheilded wire from the crank trigger to the box right? The digital sevens are very prone to electrical interference. When they put in the new box, they did not use the sheilded wire, and on top of that, they coiled the excess wire behind the new box. The owner replace the wire with the correct one, rerouted it and the problem was fixed. You also might check the coil location.

[1320quick]

Thanks for the response. I did use the shielded pickup wires with the ground on it. The dig7 is mounted above the glovebox in the passenger compartment. I ran the pickup wires away from the rest of the wires that come out of the box. I goes out the firewall just under the front cage bars that go to the front of the subframe. I have it wire tied under the those cage bars all the way to where it plugs into the crank trigger. There is no where that the trigger wires come within 6 inches of any electrical wires so I hope that is ok. What about the coil location should I check? The coil is mounted on the opposite side of the car from the dig7 box and it's in the engine compartment. I did run the two coil wires along side other wires under the dash. Do the wires to coil need to be isolated as well?

[ytnova]

Unless the box is programmed wrong, of which I have no experence with the digital sevens, I would try to move the coil wires and see what happens.

[John_Heard]

I'm guessing you just might need some fresh or heavier valve springs. I'd highly recommend checking that while you're at it.

Could be some ignition gremlin too. How much plug gap?

[1320quick]

The plugs were gapped at .030. Great idea on the valve springs. I had not even considered that but they do have 75+ passes on them. I will check them while I'm going through everything else.

[demented]

I don't think that valve springs are your problem because all this started after the mods that you made. If I was to take an educated guess sounds like the nitrous tune up is off or there is something not setup right with the nitrous controller. If your carb is jetted correctly, which from the sound of the way you describe the runs it is, the nitrous is way too lean. That jetting sounds good and if the bottle pressure is constant then I would look at your fuel system. Do you have an adequate pump, blocked filter, messed up regulator,or not enough fuel pressure. I would try the car on just the motor again. Set it up for your best runs just on the motor.Make sure that its not your ignition causing the problem. If everything runs well with no problems then I would take and bypass the progressive controller and change the jetting to about 100 hp setting. This way you can get the nitrous tuned at a baseline without hurting the motor if there is a problem. This setting also gives you a a oppritunity to play with the nitrous controller without worring about hurting the motor. Once you have all that setup the way you want, then start changing the jets and putting more nitrous to it. Process of illimination. Go back to where you started before you had the problems. Hope this helps.Having problems sucks, but having to rebuild your motor...,well I don't have to say it.

[1320quick]

demented, thanks for the advise. Looks like I have two problems. I finally got my flow tool and turns out the fuel pressure guage is 1/2 pound off from when the fuel is flowing. So when I thought I had 6lbs, it was only 5 1/2. I now set the fuel pressure with the flow tool and that eliminated the popping. Took the car out again this sunday and things were better. Made a couple of motor passes and the plugs looked great. Car still does not want to pull above 6600rpm whether it's on the motor or the bottle. It did make it's best pass ever of 9.51@146 but it's still running poorly. At this point, I'm 99.9999999999999% sure that Beyond nailed it above and the valve springs are shot. They have been on the car since spring of 2004, have over 150 passes, lots of street time and have NEVER been backed off over the winters. Yea, I know, poor maintainence on my part, lesson learned.....

[demented]

Well in that case, from the information that you gave this time, I would have to agree that valve springs are a strong possibility. They can cause some strange problems.Hope you find the problem. HHMMM,You may want to consider a new cam that would enhance your new nitrous kit (seeing how you have to match valve springs to the cam). Just thinking out loud.