Won't Run Properly - Almost a Year Now...

[PAFirefighter11]

I've posted this elsewhere and figured I'd post here as well.. This is for my '98 Trans Am.

Car info: 109k miles, K&N FIPK, stock exhaust manifold, Walker Y-pipe, Flowmaster Catback, QTP Cutout.

Story: Back in July of last year my fiance and I drove up to the Hamptons for a weekend. It's 8 hours round trip. Some of the worst roads I've ever traveled on, namely BAD potholes, bumps, construction, crap. We made it home late at night on Sunday. Monday morning, around 10am, I headed into work. On the way in I noticed some sputtering in 6th gear. It was barely noticeable. As the days wore on it got worse, so the point where it prevented me from using 6th on the highway. The rhythm is like a full auto AK-47 being fired, but not that loud of course. It only did this in 6th gear.

Eventually the SES light started blinking at speeds above 30 MPH. Codes were P0420 and P0300.

It then got so bad that I basically could not drive the car. It smelled of raw fuel, had a lopey idle (like a nice cam). It sounds great! But runs like shit. Eventually we hooked it up to a Snap On Scanner. We noted cylinders 5 & 7 were having massive misfires, with minor misfires on # 8.

After changing lots of things I finally unplugged the MAF. The SES light stopped blinking at speed. In fact, I cleared the codes and the P0300 has not come back. I plugged the MAF back in and the blinking SES is right back on. So, I tried 2 other MAF's, one de-screened, one normal. Neither changed anything. Unplugged it again and the misfire code is gone. At this point it runs so much better with the MAF unplugged, but not near normal! Only code is for the MAF being unplugged.

Things I have done/tried:
-3 different MAF's
-o2 sensors
-Checked grounds
-New PCV valve & related setup
-NGK TR-55's gapped to .055
-Vengeance Racing plug wires
-Swapped coils around, even ran "new" coils that we knew worked
-Swapped injectors
-PCM
-Fuel pressure
-Compression test (All right at or around 151)
-Tuned out rear o2s
-Tuned out AIR system
-Tuned out EGR system

I have taken it to 3 shops and a few engine builders. They've tested most of the things I have tested. Have not taken it to the Chevy dealer, but that will occur shortly. Verified fuel, spark. Not mechanic as it runs great sometime, for a minute or two, then runs like ass others.

Posting more to this shortly.

Photos of the OLD plugs when I took them out several months ago:


#8 plug lol:


This was WHILE the MAF was still plugged in:


With the MAF unplugged:

[goof4080]

Am I crazy or do u have different plugs between left n right banks? Ngk n AC delco?

I think I gapped my tr55s at. 040.

If your fuel pressure drops off could it be a fueling issue under load? Did u change the filter? If its a 98 the bumps could have stirred up rust that clogs the system, pump or filter?

I'm just spit balling here.

[PAFirefighter11]

Am I crazy or do u have different plugs between left n right banks? Ngk n AC delco?

I think I gapped my tr55s at. 040.

If your fuel pressure drops off could it be a fueling issue under load? Did u change the filter? If its a 98 the bumps could have stirred up rust that clogs the system, pump or filter?

I'm just spit balling here.

The old plugs you see in the photos were OE and NGK lol. They were gapped to .085! I measured and was like WTF...

I have not touched the fuel filter, pump, or similar. I should give in and just do the filter to see if that fixes things.

[pajeff02]

MAFs may look the same, but if they have different part numbers they could carry a different calibration. Check your ENG SENS fuse in the underhood fuse block. Unplugging the MAF forces the PCM to operate in speed density mode. If the fuse is good, then check your MAF harness and connector for issues.

[xerocks]

Check the back pressure on bank 1 you might have a clogged catalytic converter. Anything over 1.5 at 2000 rpm is excessive

[PAFirefighter11]

No backpressure issues. I've pulled the cats and have a temp. OR-Y pipe on there while I test this stuff.

Brought it today to a guy I met through LS1Tech. Real nice dude, master tech. Anyway, we used his MAF and it didn't change how hte car runs. So he checked fuel pressure on his '98 TA is at 60 psi while running, drops to 50 when turned off, and stays there for hours upon hours. Mine is at 50 psi, then drops immediately to 0 when I turn off the car. We're assuming it's the fuel pump at this point. Next on the list!

[PAFirefighter11]

Tested the fuel pump. Amps are around 7.5, which is just about what his '98 is at. Also, volume of fuel is a bit more than his is flowing, so the fuel pump isn't the main issue. Changed the fuel filter, no change in drive-ability.

Checked vacuum. -15 or so, and bouncing all over the place. Goes up to around 15-20 when on the gas, but again it's bouncing and not consistent. Per his tech book it's stating this could be a burnt valve, broken valve spring, etc. We're going to rip apart the top end this week.[BLUR][/BLUR]

[civpit510]

If its not holding pressure in the fuel rail check the regulator.

[0rion]

I agree....if the pressure is dropping you either have a bad regulator or the accordion style hose to the pump is cracked. You say running you have 50psi? It should be 58-60.

[Steve83ta]

Im the one working with PA firefighter11, and everyone has some real good suggestions. Fist and fore most and he knows this, the fuel pump has issues, it has a back check valve in the pump so as soon as you shut off the motor all the fuel flows back to the tank and the line depressurizing. While this isn't good, causing extended crank and I orginally thought there could possibly be a volume issue somewhere in the fuel system, like orion suggested a cracked hose.

But like Rick said the volume test came out fine. The vacuume readings are all over the place indicating a headgasket failure between 2 cylinders or more likely a burned or bad valve spring. We will keep you guys updated later this week, all cylinders are going to get a compression test, static and running, oh and btw its also getting a leakdown test to, meant to meantion that to you Rick.

I appreciate all the good suggestions you guys have to offer and I know Rick is too. If you think of anymore throw them our way. You can never have to many heads in the pot.. Well most of the time I believe I know whats going on but suggestions never hurt.

Steve

[0rion]

it's hard to figure this stuff out on the internet without having the car in front of us and you have the car in front of you so you know more about what's going on then we do. I can tell you to me, going off just the info here, it sounds like the low pressure is probably his issue and when that would show up is when the car is under load which is why it did it in 6th gear. Before I ripped the heads off I would be tempted to put a fuel gauge on it and go for a ride and see what that pressure is doing when the car is put under a heavy load. I suspect that's when the pressure drops. Also, he should change ALL the plugs since it looks like at least 1 or 2 people were too intimidated by that number 8 plug location to change it.

[Steve83ta]

I suspect that's when the pressure drops. Also, he should change ALL the plugs since it looks like at least 1 or 2 people were too intimidated by that number 8 plug location to change it.

All the plugs have since been changed, I don't remeber what Rick told me, but he did put different plugs back in there. I personally would have stuck with the AC Delco, but thats me.

What I think is going with that #8 plug and will know more Thursday afternoon. Whoever had that car before was having a the same problem with that plug before. I've seen it done, where the person is givin a couple of options and decides not to fix the actuall problem but push it off. Replaceings the bank of plugs where you have the oil cotrol problem in that cylinder like a valve or incomplet burns, or the worst of all a score in the cylinder wall. It could be any of them. So it runs okay for a while, couple of thousand miles normally before it comes back. And they are advised to sell the car while its running okay. Ive never covered up things like that, but Ive seen it done, and its all up to the customer anyway if they want to play it that way. Not being honest is the crappy part.

Im just hopping for simplest possible fix What am I talking about, its an LS1 they are all simple fixes

[PAFirefighter11]

All the plugs have since been changed, I don't remeber what Rick told me, but he did put different plugs back in there. I personally would have stuck with the AC Delco, but thats me.

What I think is going with that #8 plug and will know more Thursday afternoon. Whoever had that car before was having a the same problem with that plug before. I've seen it done, where the person is givin a couple of options and decides not to fix the actuall problem but push it off. Replaceings the bank of plugs where you have the oil cotrol problem in that cylinder like a valve or incomplet burns, or the worst of all a score in the cylinder wall. It could be any of them. So it runs okay for a while, couple of thousand miles normally before it comes back. And they are advised to sell the car while its running okay. Ive never covered up things like that, but Ive seen it done, and its all up to the customer anyway if they want to play it that way. Not being honest is the crappy part.

Im just hopping for simplest possible fix What am I talking about, its an LS1 they are all simple fixes

Correct, those are the OLD plugs. They were gapped to something crazy like .085. I have new NGK TR-55's in there now gapped to .055. I may go back to the Delco plugs in the near future.

I'm definitely looking forward to getting some more work with the car tomorrow!

[PAFirefighter11]

PROBLEM FOUND! Check the photos for the work done today... All are cell photos so the quality sucks:

Went to do a compression check:


Then decided to pull the valve covers - passenger side:


A little closer:


Time to rip the top end apart:






Steve has his old LS1 with 55k miles on it (He has his LS6 now) so we're using his heads, springs, rockers, etc:








We're hoping to have the heads and everything swapped over by Saturday or Sunday at the latest. We ordered all the gaskets needed from GM today. Should be here tomorrow or Saturday. I can't wait to get this thing back on the road!

[Steve83ta]

006ibd.jpg006ibd.jpgI don't want to threadjack Rick's thread but I figured I would give you a guys an update as we said answers would be today. And for everyone who agreed and said "Broken Valve spring, or burned valve" give yourself a good pat of the back as you were right. Broken Valve spring and pics to follow. And for everyone else thanks for all of your ideas. Also on a side note. Some one has been inside this engine, how do I know, the driver side valve springs, retainers and keepers are stock, the passengers however are not and see if you can tell in the photos I post. Rick might have some better ones. This is also a BIG NO NO!! That is getting corrected also.

Now on to the pics
007wkl.jpg
Driver head
008jn.jpg

Pasenger Side head, Broken spring side, can you see the difference in the springs, and the retainers
007wkl.jpg

Oh yeah the Broken one.. forgot

005dgx.jpg
Click to enlarge Pics

Steve

[PAFirefighter11]

I agree, very odd. I appreciate the help as well!

Just throwing this out there... Does this look like a cracked rocker?

[JayTA98]

I had a similar problem with the fuel pressure dropping fast after the car was turned off and a long cranking before it starts. It was the corrugated plastic line cracked.

[PAFirefighter11]

The rocker is not cracked. Strange optical illusion I guess. More progress today. Heads are off, everything is cleaned, getting ready to put the new heads on... Photos from today:









Oh haiii... Found 2 of these - of course we didn't verify which cylinder(s) they were from:


Looks like aftermarket springs, retainers... Possibly a head off of a newer Trans Am, Corvette, etc.?






Heads are going back on tomorrow or during the week (depending on family plans).

[Steve83ta]

Off topic, but JayTA98 which line? An external line? Or part of the lines that are in the tank that are part of the fuel pump/level assembly?

[JayTA98]

Off topic, but JayTA98 which line? An external line? Or part of the lines that are in the tank that are part of the fuel pump/level assembly?

Is the line in the tank attached to the fuel pump itself. I just mentioned it because OP mentioned the fuel pressure drops when he turns the car off.