Nealio240z Posted September 12, 2006 Share Posted September 12, 2006 My car will rev to 5,500 rpm in neutral. But when im under load it wont rev past 4000 rpm, (and iv got the pedal to the floor ) the rpm stays constant. It only does this when the car is warmed up... Iv gone through the fuel system -8psi @ 97gph, and the ignition system -HEI-(new coil, ecu.) Iv played with the timing countless times to no avail. But none of that would explain why it appears only when the car is warm. Could it be a vaccume leak or something? Any suggestions would be appreciated... If it helps, its a 350/350 Q-jet carb (new), proformer manifold, vortec heads,exhsust... but mostly stock... Quote Link to comment Share on other sites More sharing options...
jnjdragracing Posted September 12, 2006 Share Posted September 12, 2006 Similar condtion as mine, when we ran at sez7 the engine was strugling to turn rpms under a load, water box heating up the tires it was awsome. We normally shift at 7500 rpm, but you could actually watch the tach move up. Normally it turns up so quick you have to pay attention to driving not the tack. I plan on doing a compression check 1st, then a leak down test 2nd. I think our problem is a warped deck or maybe valves not seating or head gasket leaking just enought to affect compresion, etc. No water in oil, but under high rpm we were blowing water out of the radiator, we noticed this on the dyno. When your engine gets hot metal expands, so you could have a vaccum leak, or something not sealing well. I will let you know what we find. In your case I would double check valve adjustment, intake gasket ( seating ) maybe even a compression check would not hurt. John Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted September 12, 2006 Share Posted September 12, 2006 My car started stalling out past 6500 when I put dual exhaust on it. I haven't tried to do anything about it but I guess I'll wait in line for someone to give us an idea what's wrong. I think mine might be that it's running too rich, but I don't know if that would make it stall. I don't crank mine past 6500 so it doesn't bother me too much, it kinda acts like a rev limiter. Quote Link to comment Share on other sites More sharing options...
Lason Posted September 12, 2006 Share Posted September 12, 2006 Im thinking possible weak ignition module Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted September 12, 2006 Share Posted September 12, 2006 Do you have an adj. fuel reg. and what's the psi to the carb?? LARRY Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted September 13, 2006 Share Posted September 13, 2006 they should open up under load. The piston that operates them may be stuck. I have seen it several times, even on new or reman carbs. FWIW John Quote Link to comment Share on other sites More sharing options...
LeeMS Posted September 13, 2006 Share Posted September 13, 2006 An easy way to check Q-jet metering rods..with the engine not running gently stick a pocket screwdriver down the bowl vent [the tube that sticks up center of the car just behind the primary choke housing just ahead of the air cleaner stud] holding the screw driver sideways angle blade toward the front of the hole you should feel a spring action when pushing down. Movement will be about 1/4 inch. You then can do the same with the engine running. Leave the screw driver in the location and quickly rev the engine by hand, the little screw driver should jump when the rods raise out of the primary jets. The spring under the rods overides vacuum.A quick and easy way to check primary rod function. Lee Quote Link to comment Share on other sites More sharing options...
LeeMS Posted September 13, 2006 Share Posted September 13, 2006 Nealio240z, recheck all your basics, check for wide open throttle, check choke operation, secondaries on a Q-jet have a lock out and will not open until the choke is all the way open. An engine will rev on the primaries only with no load. You should be able to hear the secondaries on a Q-jet open they make big noise. With the eng NOT running hold the choke wide open, crack the throttle to let the fast idle cam drop[this should deacivate the secondary lock out] then give it wide open throttle, open the secondary air gate and look down the throttle bores, the throttle blades should be vertical on the primary and almost vertical on the secondary. Try these basic checks first. Lee Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted September 13, 2006 Share Posted September 13, 2006 Similar condtion as mine' date=' when we ran at sez7 the engine was strugling to turn rpms under a load, water box heating up the tires it was awsome. We normally shift at 7500 rpm, but you could actually watch the tach move up. Normally it turns up so quick you have to pay attention to driving not the tack. I plan on doing a compression check 1st, then a leak down test 2nd. I think our problem is a warped deck or maybe valves not seating or head gasket leaking just enought to affect compresion, etc. No water in oil, but under high rpm we were blowing water out of the radiator, we noticed this on the dyno. When your engine gets hot metal expands, so you could have a vaccum leak, or something not sealing well. I will let you know what we find. John[/quote'] Hey John, Paul, ( the guy with the silver/blue flame car at sezs) said it might be one piston too tight in the hole. It happened to him once. Not sure how that would affect the radiator though. Quote Link to comment Share on other sites More sharing options...
jnjdragracing Posted September 13, 2006 Share Posted September 13, 2006 Did compression check last night, all was good. Tonight doing leak down test, We are kinda thinking the MSD unit is not up to par. Tonight will tell the tale, if all checks out, then I will replace the MSD box and go try it out at a local track to see. If you notice the video Deja posted, it was balls to the wall in the 1st burnout and then it petered out? Time will tell..... Iwill keep you posted. John Hey John' date=' Paul, ( the guy with the silver/blue flame car at sezs) said it might be one piston too tight in the hole. It happened to him once. Not sure how that would affect the radiator though.[/quote'] Quote Link to comment Share on other sites More sharing options...
HICKL Posted September 13, 2006 Share Posted September 13, 2006 John, get that thing fixed and haul it to Texas in 2 weeks for Super Chevy! Jeff Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted September 13, 2006 Author Share Posted September 13, 2006 The ignition module is good, and I have 8 psi to the carb... It did this with the first carb, before I replaced it. Same with the new carb. The throttle is getting all the way open. The choke is wired open. I dont think it has anything to do with the carb... ( I could be wrong ) The engine also seems to lack power when its warm. If I slowly give it gas it will reach 5500 rmp. But not when I stab the throttle. Quote Link to comment Share on other sites More sharing options...
Z48LT-1 Posted September 14, 2006 Share Posted September 14, 2006 It almost sounds like the spark is blowing out under load. Are the plugs and plug wires as new as the rest of the ignition? Just a thought... Cheers -- Gary Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted September 14, 2006 Share Posted September 14, 2006 Time to take your car for a dyno tune....... LARRY Quote Link to comment Share on other sites More sharing options...
icewtr Posted September 14, 2006 Share Posted September 14, 2006 Tha car is to lean at the top end thats why it won't rev up.. my old 350 did this when i went to 1.6 rockers adn dual exhaust at the same time .. it was fine in the driveway but as soon as you drove it at a little over 4000 rpm it fell on its face adn didn't rev anymore just kinda stuck there..... went richer on the secondary mains by about 3 jet sizes and it works perfect now.. not to mention the wide band 02 showed it at 15.1 when it did that .. Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted September 14, 2006 Author Share Posted September 14, 2006 So do you think the problem lies with the carb(750cfm Q-jet) or the fuel pump/delivery? (holly 8psi @97gph) The fuel guage reads 8psi at the carb... Could it be flooding out at high rpm? Quote Link to comment Share on other sites More sharing options...
Alf Posted September 14, 2006 Share Posted September 14, 2006 This sounds similar to a problem I had with my v8 z31. My 307 would die at about 3,500-4,000 and not go any higher. Here's a thread that might give you some ideas. http://forums.hybridz.org/showthread.php?t=110637 good luck Quote Link to comment Share on other sites More sharing options...
HICKL Posted September 14, 2006 Share Posted September 14, 2006 Same thing happend to me. Turns out a golf ball had rolled behind the gas pedal. Just kidding, sorry, coudn't resist it. Good luck with your problem. Quote Link to comment Share on other sites More sharing options...
icewtr Posted September 15, 2006 Share Posted September 15, 2006 So do you think the problem lies with the carb(750cfm Q-jet) or the fuel pump/delivery? (holly 8psi @97gph) The fuel guage reads 8psi at the carb... Could it be flooding out at high rpm? not the carb .. just the jets .. try going larger on the main juts by like 2 sizes and maybe 2 or 3 in the secondary jets.. easy to try and if it revs up after that then tune it from there.. Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted September 18, 2006 Author Share Posted September 18, 2006 I just found out the carb was bought is for a 402, and jetted as such. They jet the carbs for a small or big blocks... This one is the small calibration. It should feed up to 385 hp.. Im looking at more like maybe 300 hp. So it should be plenty of fuel... I did a compression check and it ranged from 163psi-170psi, so all is good with that. Someone told me it could be the valve lash adjustment is to tight. Could this be true? The engine was originally a TBI set up. Do you think that I have the wrong intake manifold (edelbrock proformer for vortec heads) to mach the cam? could that be why I cant rev past 4000 rpm in first? It isnt as noticeable in 2nd or 3rd gear. The engine was a stock replacement for a truck, could the cam be set up for towing? Iv gone through my entire HEI distributor, wires, plugs, coil, capasitor, ecu, and fuel delivery... Im at my wits end and have been struggeling with this problem for over a month... If anyone has any input, it would be greatly appreciated. Iv tried everything else... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.