recently my car has been down on power and it wont climb as hard to 6k like it used to. It also breaks up when you start getting in the upper rpms. I wonder what can cause this? I'm thinking that maybe the screws in the optispark have backed out of the rotor and it is lose? The car will run great at low rpms and anything under 3.5 grand and its fine, and has no codes.

car has:
New ac delco optispark
New ac delco plugs
new ac delco o2 sensors
New autolight spark plug wires
new Coil
new ignition control modual
Egr is tuned out of the pcm and all vacum lines capped off but egr is still on intake manifold
Long tube headers
madz28 tune
cutout
new fuel filter
Cleaned maf
newer K&N filter


Like i said before the car will break up in higher rpms and has bad midrange power, I can't tell if it is detonating or missing or running out of fuel. It is definitely breaking up though. Any help would be great this car is killing my patience.

 

You need to tape a fuel pressure gauge to you windshield and take it for a drive. You can find out a bunch with this quick check.

 

Car runs fine until you hit about 4k rpm then it loses power/stutters?

Bad O2

 

Check to make sure all of your plug wires are on tight and that none of them touched the headers and burned through. I was having this same problem. Anything over3500-4000 would stumble. Ended up being a burned wire.

 

Ok no burned wires all plugs are tight. I have noticed that i can bring it to red line with out breaking up if I don't go full throttle. If i go 1/4 throttle and let it climb it will slowly climb to 6k and not break up. It will also hold 4-5 k steady without breaking up. But as soon as i go WOT it sounds like it detonates and pulls like crap. do you think maybe my full pump dieing, and just cant add enough fuel under wot because it is too much air going in the engine but at part throttle it can keep up? I am going to try and get a guage and see what the psi looks like under a WOT run.

 

did you check your o2 sensors?

 

What kind of new coil is in there. I've had bad coils do that right out of the box (was a cheapie NGK brand). Put a new GM coil back in and the high rpm breakup was 100% fixed

 

I am having exactly the same issue. Can anyone tell me how this issues got resolved? Thank you for the help

 

Is the engine stock or modified? Year of vehicle? What have you checked? What, if anything did you replace? Is this a long term problem or a recent change?

 

It is a 383 roller motor with a big cam AFR heads and an aftermarket TPS intake. It has an MSD coils and mew distributer. We just are getting into the car it is an 87 Camaro that someone else had built but gave up on it. It has 43# injectors in it and we replaced the fuel pump so we now have 45# and does not drop in pressure while driving it. We replace the MAF with a stock type from NAPA and played with the TPS up and down sitting at around .5v currently at idle. I bought a hypetech prom to see it would do anything but the same problem still exists. I can run it up if I only use 1/4 throttle but as soon as I tip into it any further than that is falls apart breaks ups and stops pulling. O2 sensor reads rich but I am not sure that is right. Seams almost like it is not getting enough air into the motor but I am lost at this point. Any help would be greatly appreciated. Thank you.

 

This is a Gen 2 SBC LT1 engine, correct?

What “TPS” intake did you use? Do you probably mean “TPIS”? Is it their “Mini-Ram”?

What brand is the new Optispark distributor?

If you bought a Hypertech PROM, sounds like you are running a 93 ECM. You aren’t going to get decent results on a build that extreme using a canned program for a stock engine. You need a chip with a full tune by a very knowledgeable chip-based LT1 tuner. BUT…. you mentioned an MAF, that would make is a 94-97. Confusing.

By “43# injectors” do you mean they are rated to flow 43 #/HR, or do you mean that they are flow rated at 43.5 PSI? And you are running your fuel pressure at 45 PSI? Do you have the vacuum compensation line attached to the fuel pressure regulator? If so, fuel pressure should vary with throttle position and movement. Even at WOT fuel pressure would drop slightly due to intake manifold vacuum due to pressure loss in the air filter and ducting.

TPS voltage is not critical with the LT1 ECM. The ECM reads the closed throttle voltage at startup, and as long as it is in the range of ~0.22 - 0.90 volts it sets it as the base 0% throttle position, and does all it’s calculations based on that.

 

It could be a TPIS with the I looking like an Injector. It is an MSD distributor. I just rechecked the timing with the plug unplugged and set it at 8degree advanced. It still did the same thing runs great at about 1/4 to 3/8 throttle as soon as you get past that it breaks up even just driving it.

I looked up the ECM number and it is a replacement but still matches the 87-88 Camaro. It is a 23degree motor built around the 87 tuned port motor. It has the newer TPIS intake but the throttle body appears to be stock. Yes it has a MAF sensor located right infront of the throttle body, but it is not a newer style LT1. The injectors are the 43 #/hr and the regulator is hooked up but I have tried running it both ways did not change much.

It seems like electrical to me because it runs so good at the lower throttle position and just falls apart if you just lean into it a touch farther with no warning just breaks up. I do not know what to look at next.

 

Why did you post this in “LT1 Based Engine Tech” forum if it’s not an LT1 engine?

Ignore what I posted, it won’t help you. I ASSumed you were asking about an LT1 engine - significantly different engine control strategy, reverse flow cooling, and a totally non-traditional distributor, flash programmable PCM, etc..

Basically, you just wasted our time.

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