Thread: 99 gtp issues

If it revs by itself you might try the TPS sensor in the throttle body...

Have a scanner on it to check for kr?

what else have you done to the engine, did you put higher compression pistons in it?

Have you taken the precautions to keep KR down? It will likely need a retune as well to compensate for the increased compression...

His issues have nothing at all to do with KR....but that is good advice to be sure to scan - it's a good rule of thumb for anyone that has or plans to mod their L67.

I +1 with Nick (bluegtp) on the TPS - but I would also swap back to your stock coil packs and see if the misfire goes away. It would be a good idea to double check plugs for proper torque and gap as well - and make sure all plug wires are snugly fit. Check inside the boots and make sure you have a solid crimp on each end.

Those are the quick and easy things to check - if none of that works - you need to hook up a scanner and start monitoring spark.

-Swash

Originally Posted by Dan

no i feel stupid for askin but whats kr ? all ive done to it is put forged pistons forged rods re built heads arp hardware msd coils and wires ngk iridium plugs and i have an 05 trans in it so i had a custom tuned computer for the trans to work in my car i also told them to retune the comp to 3800 performance spec comps and they did i also had the blower re built and a 3.4 pulley as well as slp headers and slp cat back exhaust

KR = Knock Retard (AKA- that which will put an abrupt, and often messy; end to your engine)

I give kudos to you for taking the initiative to modify your car and have, apparently; used some quality components in some key areas (MSD coils are virtually gainless, though). BUT - you really REALLY need to do some further research as to the potential dangers of modding this engine. Even the most competent of engine builders - with a wealth of knowledge; can and do have issues with KR - and if not properly monitored and remedied - your engine will suffer some sort of catastrophic failure. 99.9% of the time - it isn't "if", but "when". I've given you ZZP's "What is KR" tutorial below - but here are some further suggestions for you to consider regarding your setup and monitoring capabilities.

1) Get a custom tune You stated that you had your PCM "retuned to 3800 performance spec comps" - I'm not sure what you mean by this. Just looking at it and taking it at first glance - you have a stock tune. Not good - not good at all. At the absolute minimum - you need
to get a DHP v1 PCM tune - or have an Overkill tune (no personal experience with them, but I've heard positive things) - and I believe that TDC Racing does custom tunes as well. The bottom line - you should not - at all - be running a stock tune based upon what you stated as your current build. That's a lot of hard-earned money and time that will go to waste.
2) Invest in some type of scanner Either scan gauges, a handheld version or a laptop-based option. Modifying and scanning should be hand-in-hand. If you take the time to build something - don't you want to make sure it stays together? Scan it. Often.

Q:What is Knock Retard?

Knock Retard (hereafter referred to as KR) is the response from the PCM to cylinder detonation. KR is the measure of the number of degrees of overall ignition timing advance that must be removed from the engine to prevent detonation from continuing, thus protecting the engine from damage.

Q:What is detonation?

KR is a result of detonation. To have 'real' (more on 'real' vs 'false' KR later) KR, you MUST have detonation. Detonation is the uncontrolled combustion of the intake charge. "Uncontrolled" means that the mixture ignites via a means other than the spark from the spark plug. In most cases, the uncontrolled ignition is due to a 'hot spot' in the cylinder. Hot spots can be caused by uneven combustion, spark plugs that are rated too 'hot', lean fuel conditions, breathing restrictions (exhaust / intake), bad gas and so forth. One problem in particular that came to light for me was the head gaskets. During one of my engine teardowns, Zooomer from ZZP pointed out that, while my cylinder bores are perfectly round, the head gaskets are NOT made perfectly round. Some of the gasket material actually protrudes slightly into the combustion chamber. Since the head gasket bore linings are made of metal, that little bit that protrudes into the cylinder glows red hot, thus creating the potential for a nasty 'hot spot'. This is a good area to check and perhaps replace with an aftermarket head gasket. In other cases, the 'hot spot' is due to unreasonably high cylinder compression. Either way, the 'pinging' or 'rattling' sound you hear is the result of the actual collision of the flame front produced by the 'hot spot' and the normal flame front produced by the spark plug. Typically, these two flame fronts are opposing fronts, meaning that they are expanding, or propagating toward each other, thus the collision. Real KR does NOT occur without detonation occurring FIRST.

Q:How is knock detected?

Since detonation results in noise (the rattling or pinging sound of the two colliding flame fronts), it can easily be detected through the use of microphones attached to the engine in key locations. On both the L36 and L67 3800 engines, there are two microphones. Each one is located immediately beneath a cylinder bank and are mounted in the block of the engine directly into the cylinder water jacket. As the sound of detonation occurs, the noise is 'heard' by the microphones and the signal is carried to the PCM where it is analyzed. The PCM determines whether or not the signal provided by the microphones is knock or just normal engine noise. Knock is detected by the frequency of the signal. The severity of the knock is determined by the voltage level of the signal. Another way to say it is the voltage level of the signal will determine the level of KR. The PCM is tuned to responded ONLY to those signal frequencies that it has been programmed to recognize as knock. Anything else is engine noise.

Q:How does the PCM respond to knock ?
Engineers designed into our engines a safety mechanism for protecting our engines from KR. To do so, the PCM must respond electronically somehow to the knock signal. To electronically eliminate KR, and thus detonation, it is necessary to reduce the heat in the cylinders. Heat is a byproduct of power, so to reduce heat … power must be reduced. The PCM can reduce power electronically by retarding the overall ignition timing. The PCM converts the voltage level to a corresponding spark timing degree (KR) by which the engine should be retarded so that the detonation is naturally eliminated. The higher the voltage, the higher the KR. By doing this, the spark ignition of the combustion mixture occurs much later in the cycle of the piston compression stroke, thus reducing the effort the piston undergoes in compressing an explosion that has occurred ~15 degrees prior to TDC (top dead center). The later the ignition occurs, the less combustion that is compressed, and the less work the engine has to do. The effect of this is to cause the engine to lose power …. a noticeable amount of power. The other effect of this is reduced cylinder temperatures which immediately dissipates cylinder 'hot spots'. With temperatures down and 'hot spots' gone, detonation has been eliminated. The KR response by the PCM is limited to not exceed 25.5 degrees.

Q:What does the PCM do immediately after the detonation levels begin to fall?
Once the PCM has retarded timing sufficiently to reduce knock below the currently detected peak level, a changeable parameter in the PCM governs how quickly the overall ignition timing can be restored to normal levels (more on this later). The engine could see a peak of 15 degrees of KR from which the originating detonation may immediately disappear. However, the PCM will not instantly restore timing to pre-detonation levels. Instead, the PCM cautiously and conservatively restores ignition timing at a rate of 0.8 degrees per second. In the event of a 15 degree KR event, it would take nearly 19 seconds for the ignition timing to be restored to pre-KR levels. By the time your car sees full power again, the race is already over. This 'time' that the PCM takes to restore the ignition timing is called the Recovery Rate (more on this later). The Recovery Rate will continue in this slow fashion until KR reaches zero, KR increases back above the current recovery value, or the throttle is released.

Q:How much horsepower do I actually lose with KR?

Approximately 2 hp per degree. At 15 degrees of KR, you are subject to lose 30 hp. At 25 degrees of KR, you lose approximately 50 hp. Yes, it is VERY substantial and VERY noticeable. Please note that this is not EXACT hp lost … it is approximate.

Q:Why do I NOT want to have KR (why is it bad)?
Due to the retardation of the ignition timing, KR causes the vehicle to lose substantial power. More importantly, though, the flame front collisions are EXTREMELY harmful to the pistons. These highly volatile areas in the cylinder can cause stress cracks in your piston, which will eventually give way causing an entire CHUNK of your piston to lift right off and begin banging around inside the cylinder. This is why when the spark plug is removed after such an event, the plug end is bent all the way over. The broken piston can be VERY expensive to fix if you are not capable of doing the work yourself. DON'T EVER DISABLE YOUR KNOCK SENSORS. It takes less than 3ms to damage your engine due to knock.

Q:How do I know if I have KR?
KR is an electronically determined value based upon signal input from the knock sensors. As such, the best way to determine whether or not you have KR, and if so how much, is to use a scan tool to actually read that parameter ID (PID) from the PCM. There are three tools readily available …. Autotap, Scan Master, and a Tech 2 that can show you your KR value.

Q:What is REAL KR and what is FALSE KR?
Real KR is KR that grows with engine RPM and engine load. It depends entirely on detonation, which is dependant upon throttle position, MAF, MAP, engine load, engine temperature, and RPM. As RPM and engine load increase, the chance for KR (or higher KR) increases. As the vehicle shifts to the next gear, KR will usually make a small jump up as well due to the higher engine load.

False knock is characterized by a sharp spike to an immediately high value of KR followed instantly by the KR Recovery Rate. It doesn't grow with engine RPM or load, it jumps to a high value on throttle input and then recovers to a low value, or zero perhaps, as engine RPM continues to increase. Note that this is exactly opposite to the characterization of REAL KR. Remember, knock is simply specific noise detected by engine microphones. Because it happens to fall with in the frequency of real KR does not necessarily mean that it IS real KR.

Q:What can cause FALSE KR?
Outlined below is a list of things that can cause false knock.
Sway bar hitting exhaust downpipe - This happens typically with the downpipe of headers because that configuration puts the downpipe in very close proximity to the sway bar … much closer than the stock downpipe. The banging noise from the two metal objects hitting may resonate through the frequency band that the PCM detects as knock through the knock sensors. The solution to this is to flip the swap bar over. Because of the curvature of the sway bar near the downpipe, flipping it will allow the sway bar to curve AWAY from the downpipe rather than toward it.
Transmission oil stick hitting exhaust crossover pipe - This typically happens with the crossover pipe of headers due to their large size and proximity as opposed to the stock crossover. The banging noise from the two metal objects hitting may resonate through the frequency band that the PCM detects as knock through the knock sensors. The solution to this is to carefully bend the trans oil stick away from the crossover pipe so that the two do not touch.
Anything loose in the engine or outside the engine may cause noises that drift through the frequency range that the PCM detects as KR. Carefully check your engine! This is very vague and is intended to be vague because just about anything loose in or out of your engine that is making noise could cause this. This includes loose or noisy components in your transmission as well.
Loose knock sensors, or knock sensors that are too tight. Double check that your knock sensors are torqued to spec (14 lb-ft).


There are a lot of solid, knowledgeable people on here - do don't be afraid to ask questions - it's not stupid. Some would say you were stupid to mod your car - when you didn't know what KR was - I don't think you're stupid, but I will if you don't take some steps - like I suggested (but not necessarily what I suggested - I'm not the guru) - and then your car blows up.

Want an example of what happens as a result of KR? Take a look:

All of this (and more) was in the oil pan


Chipped 3 pistons


Something is missing here....


One of these things is not like the others...



Good luck.

-Swash

Originally Posted by Dan

i phoned 3800 performance who specializes in these cars and told me you dont need to tune the comp for higher compression as they do top swaps on the 3.8 n/a all the time and use the gtp engine tables for the ecu and they are 9.5:1 compression

The L67 engine is 8.5:1....you didn't come out and say that you were using an L36 bottom, but I assumed you were (b/c of the pistons you mentioned). So if "they" loaded L67 tables...that doesn't make sense to me.

As for the FPV - I don't have an answer for that question. Sorry.


-Swash

Originally Posted by Dan

ok yea sry i have an L67 engine but i was convinced on the rebuild by the engine shop id be better off using 9.5:1 pistons instead of the stock 8.5:1 because i wont be using the blower as much so i used them im also using the newer series 3 hot metal forged rods...talked to the shop where my car is getting scanned n they cant see much yet but the fpv is working fine....this is a weird one

So - you bored the L67, to .020 over, I'm assuming and obviously running L32 (powdered metal) connecting rods. That explains the "no need for tuning"....gotcha. I'm assuming that you also either completely removed or disabled the balance shaft? Just trying to get the whole picture, here. Any head work at all? Injectors?

-Swash

Originally Posted by minichopper6hp

That piston up there doesnt look like normal detonation damage, the ring lands are in tact. How the hell did the skirt get broken off like that? Cheap hypereutectic garbage...

Better question - how did the skirt get busted off like that and NOT score the cylinder...at all?? But hey - I'm not and wasn't complaining.

-Swash