Down on power, detonation, burning pistons - NEED HELP

[edmonds27]

Hi guys, I haven't been on here for a few months now but I seriously need some help. Bought an 85GN last spring for my son. The car had a cylinder down and when we tore it down we found #3 had a burned piston. The ring landing (between the rings) was broken in several places. The top of the piston didn't look bad. We checked all the injectors (all good), had the cylinders bored, new cam, new lifters, new pistons & rings, etc... put the engine back together. The car ran okay, but never seemed exactly right. Seemed to be down on power a little, detonation under load, engine vibration at idle, acted like a timing problem. Then while we were trying to figure it out we started getting blow by. Checked compression and all were good except #1. Pulled the piston and it looks EXACTLY like #3 did when we tore it down the first time - broken ring landing. even though we tested the injectors I thought maybe I still had a bad injector. I spoke to my engine builder AND the guy that did the machine work. The both say it's not an injector. They both said it's a timing problem. First question: Do you agree? Next question: What is causing it? Computer? Cam position sensor? I don't know where to start. Anyone have any ideas?

 

[Boost231]

Did you ever verify timing?

Did you send the injector out and have them cleaned?

How did you check them?

Did you move that bad injector to another cyl. from 3 to 1?

Who installed the cam? was it degreed? What Cam?

You said it had detonation under load? how long and you kept driving it like this?

Seemed down on power since the rebuild?

How many miles on the build?

Sorry for all the question trying to figure things out here.

 

[edmonds27]

Did you ever verify timing?

Did you send the injector out and have them cleaned?

How did you check them?

Did you move that bad injector to another cyl. from 3 to 1?

Who installed the cam? was it degreed? What Cam?

You said it had detonation under load? how long and you kept driving it like this?

Seemed down on power since the rebuild?

How many miles on the build?

Sorry for all the question trying to figure things out here.

Thanks for trying to help. I have to admit, I have quite a bit of experience with SBC (racing) but this GN stuff is new to me. I think I answered these in order.

I did set the cam position sensor according to the specs. BUt other than that I'm not sure how to verify it.

We didn't have the injectors cleaned because they were spraying fine when we tested them.

We tested them at an auto shop. They had a setup where we could put injector cleaner in a hose that fit to the injector on one end and had an air chuck on the other so you pressure it up. Then you fire it by putting voltage on it. Only thing that worried me was that it puts 12 volts on them and I know that on the car they only get 5 volts.

We didn't find a bad injector. They were all working when we tested them.

I installed the cam and then had my engine bulder come and check it outbefore we seled it up. We didn't use a degree wheel, just followed the directions on the cam/timing set.

When we got the car running we started tuning. The only driving we did was just a few short trips to see if the adjustments were making any difference.

It had decent power and pulled good when we had lots of boost, but then seemed to flatten out and detonate after it would shift into high gear. Could not go WOT without detonation.

I'm just guessing on the mileage but we really only drove it while we were trying to tune and troubleshoot it. Probably no where near 100 miles.

Thanks for responding. I hope this helps.

 

[Jerryl]

A few more questions :

1.How much boost did you run?
2.How big of a cam?
3.What do/did the plugs look like?
4.What chip/gas are you running?
5.What is the fuel pump pressure at boost?
6.Are you monitoring for KR?
7.What pistons/rings were used?

This is where a recording scantool like PowerLogger is vital.
It will tell you all you need to know, and more, before you do damage.

FYI;
Had a simliar issue with a burned piston many years ago.
Post a picture of the piston(s) and cumbustion chambers.

 

[Chuck Leeper]

Hmnn..

A couple "items"...
1. Checking an inj like that is useless.
2. The injs work at 12 v, not 5.
"when we had lots of boost, but then seemed to flatten out and detonate after it would shift into high gear. Could not go WOT without detonation."
3. What's the fuel psi and boost level when this occurs?
4. How old is your son??????

 

[Jerryl]

A couple "items"...
4. How old is your son??????

This may be the MOST important question. LOL!

Edit:
Believe me, whatever happens, you want to:
a-Get those injectors cleaned. Contact Chuck Leeper (previous post), he knows a VERY VERY good place do do that.
b-Get new injectors that are clean, WITH a matching chip.

 

[Boost231]

all good info above...

 

[edmonds27]

Hi JERRYL,

I'll try answer your qestions as best I can. I know this won't make it easier and you die hard guys are going to slaughter me on this but unfortunately we don't have a lot of data. The car is mostly stock other than: The block was decked and bored .060, heads milled, and cam upgrade. As far as I know we still have OEM ECM, turbo, etc...

1. We only have the OEM boost gauge and it doesn't work, so I have no idea. (I KNOW, I KNOW)
2. Comp Cams 69-234-4: 206/206 Duration@.050 425/425 Lift
3. The plugs actually looked very good. Even the one on the bad cylinder.
4. All electronics are OEM as far as I know and we were running 93 octane pump gas.
5. Fuel pump pressure at boost? NO IDEA
6. Monitoring for KR? - NO
7. Sealed Power cast dished pistons. Rings? - I don't remember off the top of my head. I know they weren't the cheapest ones, but I don't remember exactly what they were. The rings actually look fine on the outside. I haven't pulled them off the piston yet to check the inside.

Where do I get PowerLogger? I'm a technology guy by profession (nerd by day, grease monkey by night) so I'm sure I can handle it, but I've never done much "techy" stuff on a car. Honestly most of my engine experience is from racing an asphalt late model and we don't use much technology there.

I don't have any pics right now, but I'll get some done and posted soon. THANKS FOR THE HELP!

 

[edmonds27]

Hi JERRYL,

I'll try answer your qestions as best I can. I know this won't make it easier and you die hard guys are going to slaughter me on this but unfortunately we don't have a lot of data. The car is mostly stock other than: The block was decked and bored .060, heads milled, and cam upgrade. As far as I know we still have OEM ECM, turbo, etc...

1. We only have the OEM boost gauge and it doesn't work, so I have no idea. (I KNOW, I KNOW)
2. Comp Cams 69-234-4: 206/206 Duration@.050 425/425 Lift
3. The plugs actually looked very good. Even the one on the bad cylinder.
4. All electronics are OEM as far as I know and we were running 93 octane pump gas.
5. Fuel pump pressure at boost? NO IDEA
6. Monitoring for KR? - NO
7. Sealed Power cast dished pistons. Rings? - I don't remember off the top of my head. I know they weren't the cheapest ones, but I don't remember exactly what they were. The rings actually look fine on the outside. I haven't pulled them off the piston yet to check the inside.

Where do I get PowerLogger? I'm a technology guy by profession (nerd by day, grease monkey by night) so I'm sure I can handle it, but I've never done much "techy" stuff on a car. Honestly most of my engine experience is from racing an asphalt late model and we don't use much technology there.

I don't have any pics right now, but I'll get some done and posted soon. THANKS FOR THE HELP!

 

[edmonds27]

Hi CHUCK,

So what's the problem with checking an injector the way we did it, other than the obvious fact of course that you're not using the wiring on the car to fire them.

Are you saying the injector wiring harness DOES have 12V on it? I thought I read 5V somewhere, but I could EASILY be wrong about that.

FP pressure and boost at detonation? I have no idea.

LOL.... okay that's a fair question. My son just turned 16 in June, and only had a learners permit until this past Monday and it was broken LONG before that. The car was never driven without me in it.

 

[turboc87gn]

You gotta research on here so you dont keep breakin parts..Fuel pressure and knock and boost are critical on these cars..No one mentioned a scanmaster the scanmaster works off of the data port you can keep in the car and it will work with your powerlogger or by itself..Once you learn how to use it you will know a lot more what the car is doing..and people on here will be able to offer a lot more advice to get you on the road...

 

[Boost231]

Cant post to much right now but you need to get a boost gauge on there ASAP.

Also a way to monitor knock like the scanmaster will work for basic tunning. the powerlogger is for advance tunning IMOP. So some searching around. www.fullthrottlespeed.com has both the scanmaster and powerlogger. you will need to get the 87 ecm setup in your car first

 

[edmonds27]

I've heard some chatter in here before about the 87 ECM conversion and we actually plan to do that if we find the ECM to be causing the suspected timing problem. I had looked into this a little before but I didn't want to start upgrading on a car that wasn't running right to start with, so I didn't find out everything I needed to know. If I remember correctly you had to also change the MAF (I think)? So what the real deal? Surely it's not as simple as just swapping the ECM and MAF?

 

[Boost231]

yes its that easy, get a MAF and ECM both can be found here or GBodyParts.com Online

Contact Turbo Tweak @ TurboTweak Home and have him set you up with a chip for your car with the 87 ecm swap and no IAT unless you want to do that but its not needed.

Then once you do that get a scanmaster or powerlogger. I would do that even without knowing the issues on whats causing your detonation which is still probably due to over boosting/timing issues

 

[Jerryl]

Hi JERRYL,

I'll try answer your qestions as best I can. I know this won't make it easier and you die hard guys are going to slaughter me on this but unfortunately we don't have a lot of data. The car is mostly stock other than: The block was decked and bored .060, heads milled, and cam upgrade. As far as I know we still have OEM ECM, turbo, etc...

1. We only have the OEM boost gauge and it doesn't work, so I have no idea. (I KNOW, I KNOW)
2. Comp Cams 69-234-4: 206/206 Duration@.050 425/425 Lift
3. The plugs actually looked very good. Even the one on the bad cylinder.
4. All electronics are OEM as far as I know and we were running 93 octane pump gas.
5. Fuel pump pressure at boost? NO IDEA
6. Monitoring for KR? - NO
7. Sealed Power cast dished pistons. Rings? - I don't remember off the top of my head. I know they weren't the cheapest ones, but I don't remember exactly what they were. The rings actually look fine on the outside. I haven't pulled them off the piston yet to check the inside.

Where do I get PowerLogger? I'm a technology guy by profession (nerd by day, grease monkey by night) so I'm sure I can handle it, but I've never done much "techy" stuff on a car. Honestly most of my engine experience is from racing an asphalt late model and we don't use much technology there.

I don't have any pics right now, but I'll get some done and posted soon. THANKS FOR THE HELP!

I think it is pretty neat that your son wanted a GN instead of a Honda or something with a SBC and we all want you to succeed with this project!
The melted piston is more than likely from detonation and to find the “why”, good data will be crucial.

As far as “slaughtering you”, absolutely not. It is just that many of us have “been there done that”. Some have “done more” than others . . . . . damage that is. LOL

If you are a technology guy, you will LOVE Powerlogger. Contact TurboTweak and get the PL on an 87 ECM with the right chip. There are people working on these cars with no tech background, and you have plenty of tech and mechanical aptitude to get it done.

ScanMaster is a great tool, but does not have recording ability. With PL, you can record, and with that, you can post a log and we can provide tuning guidance.

Note:
PL® and Scanmaster® do NOT work with the 85 ECM, so you need to upgrade to get those to work. So at this point, I would look for an OTC2000 or OTC4000 monitor. These will work fine for a while but whatever you decide, you need a monitor/scan tool.

You may want to update your location so you can get some local assistance.
Aslo, read the sticky and everything you can about these cars, and post as many pictures as you can of the turbo, etc sowe can get some things verified.

 

[edmonds27]

JERRYL,

I know what you mean about it being cool for a 16 year old to want to drive a GN. I thought it was awesome that he chose a GN for his first car. AS of right now, we've ordered the parts to get the cylinder back together. As soon as we get everything in we'll get the engine back together, but I don't plan to run it at least until we get the ECM changed out most likely with a street chip from TurboTweak as suggested above. After that we might start it and check a few things out but I don't plan to drive it until we get a PL unless it's noticeably different. We're definetly getting a PL ASAP. IN the meantime here's some of those pictures:

 

[edmonds27]

Oh yea, I forgot to ask - I know I need the 87 ECM, but will the OEM 87 ECM chip work or do I need an aftermarket chip like the TurboTweak chip for the conversion? This is a street application (no racing)... no, I haven't forgotten how old the boy is.

 

[Boost231]

need a TT chip. 87 chip wont work

 

[Jerryl]

Oh yea, I forgot to ask - I know I need the 87 ECM, but will the OEM 87 ECM chip work or do I need an aftermarket chip like the TurboTweak chip for the conversion? This is a street application (no racing)... no, I haven't forgotten how old the boy is.

Funny comment about the age reference. :biggrin:

The 87 chip will work for just starting the car up to about 2-3 PSI boost . . . . after that, your tune will be waaay off. This is the EXACT reason TT has the HA specific chips! These are different animals in the tuning area.

Also, the original chips had too much timing for today's gas.
(I know, "93 octane in 85" should be "93 octane in 2011" right? . . . . )

Still wondering “why” the piston has the damage. . . . . What were the ring gaps set at, and did you verify them?

Could also be bad injector, pinched/bad wiring, bad injector driver in the ECM, too much boost/timing for octane?
(Wondering if the KR system is working . . .. . . . PL will tell )

 

[TurboBuRick]

All that work and never bothered to test the fuel system.. Tisk-tisk.