And No, I don't have TPI


Just Today I was out fiddling with My Timing and doing some WOT passes to see where I was at.

I noticed that For some Unknown reason, My car will spradically stop Revving at 4500, 5000, or 5500 In 2nd, depending on the occasion. it just Climbs up to that point and stops, flatlines...


Basically, Manualy holdin In second with My foot on the Floor, It will rev up to this point as expected, then It feels like I have hit the rev limiter, It just won't spin any higher.

One pass it will hit 4500, another 5500, and another 5000... Sporadic.

If I stay In the gas it will just Sit at whatever RPM it is at, and then occasionally suddenly "catch" again, and start to climb towads 6000 as normal.

So I figure, I am either leaning out, Or Having ignition Problems.

I tried gettng it pinned, and then pumping the throttle to see if the ACC pumpshot would help it out, but That was inconclusive.


So I suspect either the Fuelpump, Or the Dist. The carb Has worked fine for the last 5,000 Miles or So, So I don't think it is suspect. At idle I have weird fuel pressure charactorisics, So I kind of Am leaning on the fuel Pump, But Im not sure. Sometimes my idle PSI will be between 9-10, and at other times It will fly recklessly between 4 and 12 or so, the needle swinigng back and forth with every revolution of the engine.

At Speed, I can't exaclt see the Fuel pressure gauge, So I don't know )

Anyone have any ideas? this sound particuarly charactorisic of Anything ?


Thanks for any input.



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1 (faster than Ed)
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

You're going to blow your engine doing that.

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Ludicrous Speed GO!!!

 

Ummm, just a guess, but you may want to track down why you have such an erratic fuel pressure first...

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

 

Well the Needle swing On the Fuel pressure gauge corresponds to the Fuel pump Cam eccentric so I think that May be the cause, but Im not Sure.

I guess mY main Question Is, does this sound like Im leaning out, Or Getting some sort of Ignition failure ?



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1 (faster than Ed)
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

How many miles on the motor? You could be floating the valves. I had an LG4 and it would run out of breath at 4500 and just rev past that.

Check your intake bolts, they may be loose.
You need to put a fuel pressure guage on it with a long hose and tap it to your winshield to see if you are dropping fuel pressure. You should be around 6-8 psi at idle and shouldn't drop more than 2 pounds thru the run.

How old is your ignition coil?

 

I had troubles like that once, turned out to be the cat. Try hitting it and see if it rattles.

 

Bort62

I am sure glad you asked this question.
I asked a similiar question last week, posted in two differnet boards (tech/general and tranny) and got a whooping one response.

thank god you asked because I have be dealing with a similiar problem through 2 differnat motors, 2 differnt ignition systems, 4 different carbs, 3 differant rearends, 2 different fuel pumps, 2 different exhaust systems and many more changes that I am probably forgetting.

If you figure it out please reply here.

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LOBC-- SS-84

92 RS Heritage package with a 305 3" high-flow cat and pipe with a Dynomax 3" in dual 2 1/2" out.

84 El camino- 383 CID, Performer RPM, GMPP vortec heads, Holley 750 D.P.(0-4779c), Crane Energizer 274,Dual 3" Flowmaster 40 Series Exhaust, Turbo 350 (375b), TCI 2500 stall, Richmond 3.42 gears, PST Poly graphite Suspension bushings, PST steering linkage, PST springs, Monte SS sway bays, Wheels from a Third gen(does that count?)

 

Might consider a valve spring change

Can't hurt anything, can help!

plus not to spendy

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1985 IROC-Z, nuff said :P

 

Iv heard that the HEI ignition will start to drop sparks right around 4500 rpm. You might want to check everything over-maybe adda performance coil or something.

 

Fuel related is usually the same rpm, so I'm 'guessing' it's ignition. A mechanical pump will vary pressure some at idle, but you really need to check that pressure when the problem occurs to be sure. Try an ignition tune-up--coil, module, plugs, wires, cap, rotor. I have seen an ignition module do this before, but it's not all that common. Usually the modules just quit completely.


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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro

 

Typical LG4, I had and still have that problem to a point. On acceleration it would only hit 4000 rpm per gear, on down shift it would bounce to 4500. I replaced the air cleaner with an open type and improved upshift to 4500 down shift 5500. This is what happend after the change with no modifacation except the air cleaner!! Improve air flow and improve the possible RPM that your engine can achieve, improve exhaust and also improve potential RPM. But Im in a backward state of being right now I though I improved the exhaust but actually choked it and droped back the the rpm I had before .
Its a learning experiance every time!
SSC

 

Hmm, Thanks For all the responses, But I Belive that I may have Mislead some of you.

This is Not a Stock lg4, It has a Comp262H Cam, and matching Comp 981 valvesprings, valve float is not the issue.

As far as the Motor Not having the power, that is not the issue either. I spin the Motor To 6 grand regularly Racing, And it just started this today.

Im going to Go ahead and replace the Module, The wires and PLugs are all In good Shape as far as I Know, Not really any reason For them to be bad They are fairly New.

AS Far as the fuel pressure, When I get a Chance Ill Run the line Up to the windsheild and Check it, I have a Feeling this is the cause.

Thanks For all the Input, Let me know What you Think



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1 (faster than Ed)
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Mine isnt either comp270H but still it would only hit 4/4500 RPM.
I would check that fuel pressure out but 1st I would return the timing to the point where you were before and see if it helps.
Ah the possibilitys are endless.
SSC

 

Wow thats alot of Cam For a 305, What heads are you using ?



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1 (faster than Ed)
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Stock as a rock heads Funny thing is although the cam is considered agressive it runs exactlty like a typical LG4 and gets 22mpg in the city.
SSC

 

Hmm, I can Barely Crank out 15 mpg on the Highway.




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1 (faster than Ed)
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype