ive been screwing with this truck for a couple months and for the life of me i cant figure this out. heres the deal. im running a stock shortblock with vortec heads, XE256 cam and performer rpm intake. 90lb injectors at 18 psi.

i started with 61lb injectors at 25 psi. i had the tune nearly perfect. it was a tad lean on AE and it was lean around 4400-4800 rpm. i needed more injector.

put in the 90lb injectors at 18psi. i have added fuel to the point it literally rolls black smoke and the WB reads 9.8:1 and i still get lean detonation at high rpm. now youd think it has to be timing. but ive had timing as low as 20 degrees. it runs best at 32 deg so thats where i leave it.

what really gets me is that some days it runs just fine and other days it runs like pure crap. im beginning to think its an ignition issue.

sometimes if you hammer it it will just make alot of noise and go nowhere for 5 sec or so and then start to make power. any help appreciated. BTW i want to try a different bin. i started with BJYM but its nowhere near stock. so if anyone knows of a better bin to start with let me know.

 

Too much fuel can cause the engine to knock.

 

If youve had the engine for a long time and youve also been running it really rich it could also be carbon issues. Too much carbon in the chambers will raise the compression, and act as a source to ignite the fuel prematurely.

Additionally, it could also be the result of the engine going lean on AE, and going into detonation. That will dump a lot of heat into the engine, and set it up to continue detonating after the event that triggered it has passed.

And, it could also just be an ignition issue, and false knock.

Do you hear any audable detonation when it happens? Does it happen when you slowly roll into the gas rather than getting on it?

 

sometimes it will knock to oblivion and pop and just plain sound like its going to blow apart, and then later on it may just have a slight hickup for a second and go. i guess i should pull a couple plugs

 

this sounds possible. the cold weather is a PITA to get AE right. today i played with the AE MAP and TPS filter and it seems to have helped the cause alot. i just thought the engine would recover after going lean on AE. didnt think it would continue to knock

 

drove great all day, AE was actually a tad rich today after playing a bit more. i let it sit for 2 hours get in it and its SOOO lean its reduculous. today it would fly past 5800 rpm and hit the rev limiter. tonight it would hardly go past 4500 and sounded horrible the whole time. anyone want to look at the datalog?

if i roll on the gas gently it still goes wayy lean.

 

edited

 

false alarm on the vaccum leak. it isnt leaking.

now wont a missfire cause the wideband to read lean? im pretty shure this is correct? because my AFR is very unstable at the rpms it breaks up at. it varys from 11:1-13.5:1 rapidly. as soon as it goes to 13.5:1 the engine makes a buzzing sound almost like a soft touch rev limiter. im assuming its a missfire.. i have taken care of AE issues also.

 

whitelightnin92, sounds like a ignition problem to me as well. You might want to try changing the coil and module, but I suspect that it may be a problem with the wiring. Most likely the wires from the distributor to coil. I've had those give me fits, even when there appeared to be noting wrong with them. Only cure was a new wires and plugs from GM. Also, the outer wires leading to the distributor can be problematic as well.

 

hey thanks for the reply. i have new taylor wires and Delco plugs. but the cap, rotor, and coil are about 2 yrs old. when i put a new dizzy in(2 yrs ago) i got an elcheapo from autozone that came with a module because i was short on cash. so my first guess is the module. thanks

 

got a 369 module from a friend tonight. going to try it when i get a chance. it gets worse everyday. im waiting for it to DIE. but i think i know the culprit. i had a low voltage from the altenator for a month or so untill it finally died and i replaced it. i think it killed my module

 

Hey white just slap me If this makes no sense but rich or ing misfires would result in cooler exhaust and a richer reading, unless combustion temps equaling chamber combustion temp is occurring in the exhaust due to unburnt mixture, just seems unlikely without compression. Check them plugs (BURRRR) for a good read. Or it just might be that lean and result in the hot exhaust & lean read from the o2. How high are you running PE? We KNOW that she has been lean before the injector upgrade. I know you want to tune this out, just keep an eye out for mechanical discrepancies. I feel heartless to mention valve seats after all you have been through with this build.

 

This is a magor problem with the wetflow systems. With a wetflow system, the fuel actually has a great deal of influence over the temperature of the manifold. When the fuel enters into the intake, it will flash over to a vapor in the low vacuum, and pull lots of heat out of the intake. So much so that the intake can actually be cooler than the ambient air. This causes the temperature of the manifold to constantly change with varying driving conditions. As the temperature of the manifold changes, so does the AE requirement. When the manifold is cool, the fuel will readilly wet the intake walls and settle out. When its hot, the fuel cannot settle, and it stays in suspention. This means that the required MAP AE is a moving target.

Now, with that said, it could also be another issue. The engine still should recover after about 5 seconds or so of going lean once the manifold has been fully wetted internally. If the engine continues to go lean, then there are other issues at play as well. Basically, with MAP AE not being right, the engine will go dead lean on tip-in, and maybe even backfire. Once it recovers, it will then run (or at least should run) normally.

The ignition is also a definite issue with the older HEI distributers. The problem is that the distributer base serves as the heatsink for the module, but the base also picks up heat from the engine. This means that the coolest the module can get is about 180 deg F. In a performance application, the module can run much hotter. The underside of my distributer would get hot enough to burn my fingers after i drove the car real hard. I used to go through modules left and right. They would last, at most, about a month, and then die. This sort of sounds like what you have. The engine will basically run worse and worse until it finally just doesnt start one day.

The newer distributers for the vortecs actually have the ignition amplifier (basically the module) mounted externally with its own heat sink. This means that you can put the amplifier and coil somewhere nice and cool. MUCH better than the old CC-HEI system that GM used to use.

 

Sure makes a good argument for an aftermarket cooler/heatsink for the underside of the dizzy. Thanks dimented I really don't think I have all the answers white needs.
I'll just slip back in the shadow of an EFI master now, back to my studies as a good student should.

 

The is good info in this thread on heat sinking for the ICM:

https://www.thirdgen.org/forums/v6/1...-why-does.html

Could also use a sink with more fin area. But figured it was better then none.

RBob.

 

thanks guys. i threw that module on along with a cap and rotor i had laying around. it runs 100% better. now on to another question. i have much more power and better throttle response but, at 4500 and over it still is at a loss for power. now, knowing what my VE looks like and what it looked like with previous ecms i would think it is getting way too much fuel. but according to the wideband when this happens im at 13.5-14:1..... and im not static(5000 and over im very close to static, about 90%DC). im going to ignore the wideband for now and lean it out.

BTW. after the ignition upgrade and playing with map multipliers AE is excellent

 

Be careful swapping from one module to another with a different number. It can change the real timing dramatically. So much so that a complete re-tune of the SA can be required.

RBob.

 

its a 369 module wich is OE. i may need to pull some timing as it advances timing a bit more at high rpm that the autozone replacement i imagine. i need to do a datalog

 

just an update. its up and running great. i was wayy rich. i have it tuned great now. i cannot believe it had me going in circles for so long