Need advanced help with detonation

[HBHRacing]

I have been doing some searching on here looking to see if this problem has come up before but I have yet to see the same symtom or any information new to me. So I hoped that I could get some thoughts and maybe work through the problem here. I stuck this in the advanced section since it;s going to be a good bit detailed and since I can keep up with any discustions about it from expirenced people here.


First a little about me. I am a mechanic. I ahve been one for just under 5 years. I have a strong backround of electrical diagnostics and computer troubleshooting. I own a 96 Z28 and frequent several fbody boreds. I have been working on a friends 3.8 for a while now and am still no closer to an answer.


now about the car. it's a 01 firebird with a 3.8 Totaly stock when purchesed, He notices soon after getting the car that he had what he called a "miss" after talking about it I desided to take a look for him over the weekends and get it fixed. Since he still had a warrenty he took it to teh dealer first. They condemed 4 bad plug wires. replaced them. No help. went back, they said one coil, replaced that and no help. Then hey changed the PCM (gota love dealers) no help. So he got sick of that and let me take a look.


after drivng the car and feeling what it was doing right away it didn;t feel like a miss to me. it felt like someone had a switch to cut off the motor and right about at 4,000 RPM while acelerating would turn the motor off for a split second and turn it back on. I would more like to call it a "surge".

My first thoughts were fuel pressure. checked fine. inspected the vacuum and ran a test based on MAP BARO and MAP KPA and came up with 20 inches of vacuum so we were good there. Check all of teh computer systems. Everything nominal. I tied into the injector control with a graphing meter to look for a drop out while driving, nothing.

The more that I heard it the more it didn;t make sence. I then was listening closly and figure something out. everytime it "surged" I heard something. it was an audible "ping" My thoughts then went to detonation. So I looked at the knock retard. while driving I randomly got 2-4 degrees of KR. when we felt the surge I could see anywhere from 6-14 degrees of KR. I knew we had something.

I have tried everything that I could think of so far. everything looks good. WE played with the knock sensors trying to emiminate a faulty one. to no avail. it can not be false knock since you can hear it ping. he also to emiminate false KR unhooked both knock sensors (bad idea I know) and still it did the same.

he recently changed plugs and wires and ran 93 octane. still no help.

I know this is long but I could really use some imput. the next thing that I am having him do is take it for a thourgh top engine clean. I wanna get rid of any biult up carbon that might be getting super heated.

I apresite the time.

[Speed Freak]

I bet his cat is clogged. It's a common problem.
It happened to me 3 times before I changed to a high flow.

[AllTheGoodNamesAreGone]

ICM.. try swapping out hte ignition controll modual too..

i "dont think" its the cat after reading the description above.. but its not impossible..

[Turbo V6 Camaro]

what plugs did you buy? and what are they gapped at?

umm that a wierd one,

you could try seafoam to get the carbon out of the motor

[Turbo V6 Camaro]

oh check the IAT sensor make sure its not telling the PCM it getting like 30* air and advancing the timing to much

[HBHRacing]

well. He's still trying to get teh dealer to do something about it. I would try an ICM but it's more money then he would like to put out there to "test"

I doubt it's teh cat either but now that I think about it I have yet to do a back pressure test to compleatly rule it out.


I "belive" he got the NGK TR55 plugs but don;t quote me on that. as for the gap I am unsure but I supose that we could try closing the gap a little bit.

as for the sea foam. I am stealing the top end cleaner kit from work and running some BG fuel system cleaner in through the brake booster line but I am still going to recomend that he goes through a thourough injector flush/clean to really get the cleaner to the pistions.


Thanks for all the help thus far. I look forward to further insite.


IAT was good. However. He installed a 160 thermo and I made him a manual fan switch. And now he has the issue of the ses light and the temp gauge dieing. Apearently someone from here said to install a resister in the IAT. I am not fond of that idea. If the car was perfect I would say what the hell but I do not want the computer to add any more timing especialy once the motor is hot. There must be a way around that without such a dramatic change in the IAT imput.

[arthansen]

I could not run the 160* thermo, had to go with the 180*. Hypertech says this is a problem with the 2001's. The 180* does not throw the code.

[HBHRacing]

Thats kinda what I told him. But with the fan switch I made him he can keep it plenty cool. whats the stock thermo a 195?

[Turbo V6 Camaro]

if he put a resitor in the IAT and it was to high it will advvance the timing to much

[malice10985]

Your description sounds a lot like my car when I had a clogged catalyst. I had a flowmaster muffler at the time, and I noticed that it started to get a lot quieter over a 2 week period; on top of the other symptoms you desribed.

I would seriously check the cat.

[2short]

Hi Harlan :Waves:

Sorry can't help Jeremiahs problem, just wanted to say hey lol.

btw its camarochrisz28 from fbody.

[HBHRacing]

lol. hey man. Nice to see a friendly face around here.


he did not as of yet put teh reister in the IAT cause I told him to wait untill I could scan the computer again and see what kind of readings it was giving off. I mean he IAT isn;t gona control that much advance but still with it this bad anymore then normal could be a real problem. I might take one look at the readings and tell him to through a 180 in it to be safe.


As for the cat. Yeah, I really should just go for a back pressure test. I more or less ruled it out already but would like to have the correct readings to be 100% sure.

[Coriya71]

Detonation/Spark Knock
Checks Action
DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Preliminary Checks Refer to the Symptoms .
Search for bulletins.

Fuel System Test for incorrect fuel pressure.
Refer to Fuel System Pressure Test and Fuel Pump Electrical Circuit Diagnosis .
Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
Test items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean Bank 1 .

Ignition System Inspect the spark plugs for proper application.
Refer to Spark Plug Usage in Engine Electrical.

Engine Cooling System Inspect for obvious overheating problems:
Low engine coolant.
Restricted air flow to radiator, or restricted water flow through radiator.
Electric cooling fans operation. Refer to Electric Cooling Fan Diagnosis .
Correct coolant solution should be a 50/50 mix of GM approved antifreeze coolant and water.

Engine Mechanical Excessive oil in combustion chamber-Leaking valve seals.
Low cylinder compression.
Combustion chambers for excessive carbon buildup. Clean using Top engine cleaner. Follow instructions on can.
For incorrect basic engine parts. Inspect the following:
Camshaft
Cylinder heads
Pistons, etc.
Refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Additional Tests Test for proper EGR system operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .
Test the transaxle range switch input with the vehicle in drive and the gear selector in drive or overdrive.
Test TCC operation. A malfunctioning TCC can cause the engine to spark knock. Refer to A Diagnostic Starting Point in 4L60E Automatic Transmission.
If scan tool readings are normal and there are no engine mechanical problems, fill the fuel tank with a known quality gasoline that has a minimum octane reading of 87 and re-evaluate vehicle performance.


Also if you want to check the ICM without buting a new one, take it to autozone, they'll test it for free.

[HBHRacing]

I can test the ICM better then they can. But resistence and voltage tests are usulay inconclusive when dealing with an intermitent fault. the fault must be recreated while tetsting in order for it to mean much of anything. For the most part the ICM test is looking for an open circut that would point to a no spark situation, not an intermitent fault.


There are few things that we have not ruled out that could cause detonation. Most of them I will finish rueling out next weekend when I look at the car.

I will be doing..
a top end clean and a exhaust backpressure test as well as another full systems check with the M.O.D.I.S

if the back pressure test shows anything then I will have him take it to teh dealer and have them perform the same test and replace the converter under warrenty.

If the top engine clean shows any kind of improvment then I will have him take it in for a very very good flush and clean.

[HBHRacing]

I would just ike to add something that I left out. It seems to go along with combustion chamber temps. The hotter the car the more severe the ping. Thats why we ran a manual switch and 160 thermo. obviously as the combustion temps rise so does the ability to ignite the fuel. So it;s going to get worse then but I just thought that I would add that to the story