Thread: Lost??????

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Ok..... I am working on a 85 mustang 5.0. I have a problem with timing, and here is what it is doing. When it idles it is good.... no back fires at all. When it is driving on the highway.... no back fires! But when i get in to the throttle, it sputters over 3000 rpm and sometimes lower. I know it is missing but I put a new distributer in, and a stock spark box. New spark plugs and wires. Here recently, I put nitrous on it, but nothing too radical. Just a 75 shot. It is carberauted, not fuel injected. We have the fuel line teed off and running to the carb and the fuel solenoid. The pressure gauge, on the fuel says 9psi and 7psi is what the minimum fuel pressure that engine should be at I believe. Thanks alot in advance......I know that is alot of questions, but I am trying to get to the races tomorrow and would really like to get this fixed.

Adjust for 5 1/2 lbs max fuel pressure at the carb inlet.

how am I supposed to do that? It is a mechanical fuel fump. I did not know that they were adjustable.

Install a fuel pressure regulator between the pump and the carb. Monitor the pressure at the carb inlet. The SUM-G3131 or HLY-12-803 will work fine.

http://store.summitracing.com/defaul...h.asp&x=31&y=6

I'm not trying to second guess you but I do not understand. How is turning down the fuel pressure going to stop it from stumbling? Wouldn't that make it worse? What is the engine doing (in your opinion), to make it worth doing that ( turning down the fuel pressure)? thanks alot

The needle and seat in the carb are only capable of shutting off the fuel supply to the bowl at pressures not to exceed 5 1/2 to 6 psi. Anything over that will overpower the needle and flood the motor with fuel.

So it is running rich, and the timing COULD be ok? If that is not it.....what else do you think that it could be?

I can pretty much guarantee you that if you are supplying 9 psi to the carb, that is your problem.

Thanks Alot !!!!!!!

You're welcome, good luck

Tech1 please help the races are tonight. I put the regulater on and i set it at 5 1/2 and now i can ajust my air & fuel and also idle i couldnt before thank you. But now it still miss fire also i was told that my distributer might be off a tooth or two i checked its dead on. Also someone told me that it might not be getting enough fuel from the fuel line cause it is teed off to the fuel solinoid i dont see how it would not be getting enough fuel when the nitrous is off. An one more thing someone also told me the timing chain might be streched please help.

It seems you've already addressed the ignition system, so I'd maybe be looking elsewhere. Warm the motor and run the valve lash again. Back off each rocker until it clacks, then tighten down slowly until it quiets, then give it another half turn. You may be holding one or more valves slightly off the seat. It might also be one or more burnt exhaust valves. Do you have time to do a compression check on all cylinders? If you do, be sure to wire the carb primary blades open so the motor can breathe.

By the way, you installed the regulator so that just the carb is regulated right? You don't want the nos fuel solenoid regulated down so far that the motor goes lean when you spray it.

I have to leave to go to work now, so I'm in hopes that Denny, Mike or one of the other diagnostic gurus can help you further. It's tough to diagnose a miss by long distance.

I am still lost on this whole situation. I have replaced every ignition component and checked spark to all cylinders by using an extra spark plug and then hooking it up to every wire and starting the car individually. The funny thing is, the car does not run any differently when I do this. I would figure that basically dropping a cylinder would cause it to run worse. Also, if my lash was not set correctly, wouldn't I hear a clack to begin with?? I got it to run better at idle now by advancing the timing but I do not know how far it is advanced. (I am afraid to know!!!) Now that my idle is ok, it runs fine through the rpm range but backfires tremendously when I let off of the gas. Since the timing is advanced so far I know better that to use the nitrous Hopefully this may help a little bit. I also was thinking that maybe I am not getting enough spark. I have an MSD box that I can wire in to test to see if that is the problem. Would you recommend that? Appreciate it alot!!!

Pull all the plugs, wire the primaries open and compression test all cylinders.

i dont know tech you've covered it pretty good. need to know the comp. and a vac. reading wouldnt hurt.