Well, I'm at a loss here. Just so everyone knows, I have a '95 Lt1 in my '98 S-10. Last year It ran great, no problems except for a little leaking here and there. This year I roll it out of the garage with all the leaks fixed, and I put on a welded and ported intake, and a new 52mm throttle body. All is good..... so I thought! Now my truck willl not for the life of it get past 5500 - 5700 rpm?? To describe it in a simple way, At full throttle it goes like hell untill 5700rpm and then it acts exactly like the throttle cable breaks. That's the best way to describe it. No stumbling , no backfiring, no nothing, untill I let off the gas and step on it again, then it resumes in the next gear untill it hits 5700 prm again and it goes on and on!!!

If I only get on it at part throttle, like say 75%, it works fine but doesn't give me the full acceleration effect... what's the point of having an LT1 if I can't use it all?

Now... I've checked and cleaned the map sensor, adjusted TPS sensor to proper voltages, the optispark was brand new 5000 mile ago, plugs wires all seem to be good, I've checked all the wires from front to back in my truck and everything I've seen is perfect(no burnt or cut wires), all fluid levels are good, keep in mind this truck had it's LT1 swap last year and all engine sensors including the MAF was brand new last year.

I have used data master and at full throttle and at about 5500 - 5700 rpm the maf reads about 280 grams per second and then it just instantly falls to about 40 grams per second... even with the throttle blades still wide open!!

I know it's not good to rev the snot out of an engine while in park or neutral but just to try it I reved it up right to the limiter just once to see if it would give me any trouble and it reached 6500rpm no problem.....what gives?

And for info sake: '95 OBD1 LT1, Lt4 hotcam, slightly ported heads, 1.6 RR with LT4 springs, BBk52mm throttle body, LT4 knock module, welded and ported intake, 30# injectors, shorty headers, true dual exhaust, and otherwise stock bottom end LT1.

WOW... I hope somebody has the time to read all of this and give me their thoughts!

 

rev limiter?

 

Had a car like this on the dyno once and had a hell of a time figuring it out. It was bad valve springs.

Rich Krause

 

Yeah.... I've been hearing this a few times now! how can you tell if they are bad??? They were brand new last year. In fact, the whole motor was new last year.

If there's an easy way to tell if they are bad I'd like to hear it!

Gettin my valve springs off shouldn't be that hard, My engine bay is a whole different ball game than an F-body.

 

Any good engine shop will have a valve spring tester.

Rich

 

I say rev limiter. My LT1 has a limiter around 6,000.

 

I'm going to have to say no to the rev limiter idea... only because I've had my tuning done by PCMforless and I've had Bryan look over my program a few times..(I think he's getting annoyed with me! ) and Bryan says that the rev limiter is set at 6500rpm!!

I'll have my engine builder look over my valve spring specs and see what he has to say about this... he can just test them in his garage for me. And hopefully soon I can figure this out!

Any more ideas would be appreciated still, and I'll keep ya posted as to what the outcome of the valve spring issue is.

Thanks

 

not to change the subject, but how did you safely clean the map sensor and adjust the TPS to the proper voltages? maybe thats what i need to do....

 

Maybe you misunderstood me.. My map sensor I just pulled off and cleaned it carefully with a q-tip.... and the TPS sensor I have is slotted because I needed to adjust it with my new throttle body. You can use a volt meter or do like I did and use datamaster, with the key in the "on" position and datamaster running I loosened the TPS sensor just enough so I could move it, and by watching the TPS Millivolt readings adjusted it to around .5 - .6 millivolts while idleing..... that seems to be the norm.

 

Might be a long shot, but do you have an aftermarket ignition that has a rev limiter built in?

Jody J.

 

Yes I have an MSD 6AL....but I am using no pills currently. And just for fun I tried putting a 7000rpm pill in it and still the same.

 

Have you tried running it without the MAF? Sounds like there may be a short somewhere or something. Stinky, the world's most annoying cat, says to try that to narrow the problem somemore.

 

I'm sorry..I didn't mention that I did try that already. I've done so much that I've forgotten what I've tried already!

Thanks for the replies guys..... keep 'em comin'

 

does it pop out the exhaust or back up the intake any,

Doesnt a floating valve (weak spring) pop and snort?

 

No popping or backfiring.... It acts EXACTLY like someone just cut the throttle cable on me! I floor it..and when it gets to 5500 - 5700rpm.... bang! it acts like I let off the gas.... it's a very smooth shut down?!, It is giving me no clues!!