ANOTHER frustrating lt1 misfire problem...

[kris72079]

Ok, to start let me say that I have reviewed 100's of posts on this and other sites to resolve this problem. While things have improved this issue, nothing has resolved it.

I have a 1997 Camaro with lt1 and M6. The lt1 is a new rebuild (less than 100mi. on it). Immediately after install it had a cyl #4 and #8 misfire that made it not driveable. The cap and rotor were new, and then after a moment of thought realized that the plugs were not changed. New Delco plugs were installed also the fuel filter was changed. That made a vast improvement, #4 & #8 cyl misfire gone but now a rather bad #3 misfire.

Next fuel injectors were all removed and seals were changed, fuel rail was cleaned, and injectors were reinstalled in new locations, That helped enough to make it driveable for me to get it to my garage. Tired of driving to someone elses house after 10hr workday to mess with it! Then the valves were adjusted trying to track down the #3 misfire which did almost nothing.

Next I installed a new optispark. This helped ALOT, but not 100%. To this point it would run fine over 2300RPM but misfire with flashing SES light below that. After opti I can drive it with almost no issue except for 6th gear (1500RPM @ 50mph) it hitches like crazy and MOST of the time will trip the flashing SES light until I go to 5th and get the RPMs up. Throttle response is pretty good with the exception of the occasional hitch when going from cruise to WOT. Now I only get the misfire when running in 6th (low RPM, high load) and after it is driven for 10-15 mins and parked at idle. It will idle ALL DAY LONG from cold with no SES light or noticeable skip, but after driving it and return to garage flashing SES light after 10 seconds of idle, run up RPM for a few sec and flashing SES goes away, return to idle and in 10 sec it comes back.

Yesterday I replaced the intake elbow, no help but was needed. This morning I sprayed the intake gasket area, vacuum lines, fuel injectors, EGR valve area, and intake elbow to air box with starting fluid while idling with no change in RPM so vacuum leak is not suspected as far as I know.

After changing the opti The misfire came back almost immediately on the #3 cyl, but after some drives I have had it come back on the #4, #8, and #3 cyls at different times. It is almost non existent if the RPMs are kept over 2k, but after significant DRIVING warmup it will return at idle (on one of those 3 cyls). Also, this morning I had my scan tool (INNOVA 3160b) set to record 50 frames before and after DTC. It set P0308 (#8 cyl misfire). The results at trigger frame are as follows:

Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load(%) 8.6
ECT(F) 176
STFT B1(%) 0.0
LTFT B1(%) 21.9
STFT B2(%) 0.8
LTFT B2(%) 18.0
MAP(inHg) 9.7
Eng RPM 2030
Veh Speed(mph) 44
Spark Adv(deg) 32.0
IAT(F) 39
MAF(lb/min) 3.0
TPS(%) 8.2
Air Status OFF
O2SLoc B1S12B2S12
O2S B1 S1(v) 0.625
STFT B1 S1(%) -0.8
O2S B1 S2(v) 0.825
STFT B1 S2(%) 99.2
O2S B2 S1(v) 0.455
STFT B2 S1(%) 0.8
O2S B2 S2(v) 0.845
STFT B2 S2(%) 99.2
OBDSup OBD2

Looking back in the results prior to DTC set this stood out to me:

-60.5 seconds -58 seconds
STFT B1S1 28 STFT B1S1 50
STFT B2S1 30 STFT B2S1 50
Absol. throttle pos 100 Absol. throttle pos 100

Reviewing the 100 frames recorded (50 before and 50 after DTC) more often than not the B1 S1 readings are high during high throttle positon leading me to believe that it is trimming more fuel during high throttle situations because it it too lean?

Anyways, looking for an outside set of eyes and ideas as I am getting frustrated and tired of throwing parts at it. IDEAS?

Thanks!

[USMC]

Kris,
This sounds EXACTLY what my m6 Trans Am did and how it acted after a full tune up. Long story short my brand new plug wires were the cause of my multiple misfire, sluggish responses and hi load low RPM test. It had a slight hesitation before the tune up which promted me to give it a tune up. I bought MSD wires and dissolved my issues. I had a friend connect his computer to it and yep almost the same exact thing. Good luck

[cocobolo95]

I will suggest looking at the wires at night with engine running. See if you have any arcing. Spraying the wires with a mist of water beforehand can help pinpoint spark leakage.

Have you tried a new coil. Often time missing at a high load is caused by a bad coil.

[kris72079]

The coil and wires are new MSD installed at time of build, not to say that they aren't the problem because at this point ANYTHING that I've replaced is back on the table as an issue. I have checked them at night for arcing and saw nothing. What troubles me is that 1. the misfire comes and goes from three different cyls at different times; and 2. that it has improved with numerous fixes. I will try misting the wires and see if that does anything. Anything else?

[kris72079]

Okay, so now WAY beyond f'n fed up with this car!!! Today took all day and replaced plugs and wires (again) based on previous suggestions. Could have done it much faster but where this motor was just put in I wanted to see that I didn't overlook anything during the install. I took off y-pipe, starter, alternator, power steering pump, A/C pump, all accessory brackets on the right side, water pump, air injection pump, and removed radiator to be able to see EVERYTHING and change the plugs and wires with no questions about cracking a plug, tugging a wire out of the end boot, crossing wires, etc.

Everything looked good during my inspection so I proceeded to put it all back together after carefully replacing plugs and wires being certain to have proper routing of the wires. Here's where my day goes to crap. I start it up and it IMMEDIATELY throws P0304 and P0154 codes. Revving it does nothing like it has before. I clear it and almost immediately it throws P0308 and P0154 codes. I take it for a ride. Its running like crap, no backfiring or noticeable miss just sluggish and down on power. I check and clear codes several times during a 3 mile ride, no more P0154 at all but MANY P0306's and few P0304s and P0308s each and one P0303.

Okay, I know everyone is probably gonna jump all over the P0154 code and tell me to change the upstream O2 sensor on the right side, I get it. But I'm getting tired of throwing parts at this thing. I'm a avionics technician in the Air Force, if I threw as many parts arbitrarily at a jet as I have this car I'd have been in to see the maintenance officer by now. I'm not against changing that O2 sensor, just looking to see if there might be something else that I am missing. Also, the P0154 code came and went, ideas why? Also, where did the P0303 come from? its on bank 1, where my P0154, 0306s, 04s, and 08s are on bank 2. Did the knock sensor just get it wrong? ARRGH!

Also, to throw something else in for confusion...I hooked up my fuel pressure tester to the schrader valve on the fuel rail and key on engine off pressure is 24#, at idle 28#, and dips to 18# at WOT. I'm not certain that this is really doing much for me negatively though as I've always had no issues at high revvs until tonight.

Not looking forward to dumping that Y-pipe again to change the O2 sensor.

Questions? Comments? Concerns? Potential Buyers? (haha)

[hendy94Z]

Your fuel pressure key on engine off should be in the 43# neighborhood which could explain your bank 2 issue. The 303 could have simply been a fluke

[cocobolo95]

Your fuel pressure is low, but before you go out and buy a fuel pump, make sure the pressure regulator isn't stuck a little bit open. Then check your injectors for leakage. Fuel filter should be changed if it hasn't been already.

Having low fuel pressure can cause a lean misfire condition. Hook up to a scanner that does real time sensor data and look for injector on times being way high to compensate for the low fuel pressure.

[kris72079]

Originally Posted by cocobolo95

Your fuel pressure is low, but before you go out and buy a fuel pump, make sure the pressure regulator isn't stuck a little bit open. Then check your injectors for leakage. Fuel filter should be changed if it hasn't been already.

Having low fuel pressure can cause a lean misfire condition. Hook up to a scanner that does real time sensor data and look for injector on times being way high to compensate for the low fuel pressure.

So are we leaning towards fuel pressure being the critical error as opposed to the O2 sensor? If the fuel pressure is the issue then why is it only occurring on bank 2? The fuel rail feeds both banks from the same batch of fuel, so how can it starve only one side? Also, if its fuel pressure wouldn't you expect fuel starvation at high RPMs when consumption is greatest? All along its been better at high RPMs and crappy at idle or at low RPM cruise. Absolutely not doubting anyone here, to the contrary I put this out on here because of the knowledge I see thrown around on this forum, just trying to justify it in my head...

Also, filter is new, and the injectors have all been sprayed with starting fluid with no change in RPMs (injector seals are new) so no leak suspected there....

[hendy94Z]

The feed to bank 2 travels further than bank 1, low fuel pressure won't allow as much to hit 2. Far as the rest I'd be shooting in the dark so someone else can explain that

[kris72079]

This morning I went out to check the fuel pressure regulator. As a baseline I checked things and this is what I started with: KOEO 26psi, engine started 24psi, WOT 18psi. Now with vacuum line off FPR and intake port plugged: idle 24psi, WOT 18psi. Also there appears to be no leakdown to point to check ball or injector leak. I also crimped off the fuel return line and there was no change in pressures at KOEO, idle, or WOT. Fuel pump?

Just looking to straighten out my damn misfire (see whole post)!

[cocobolo95]

Fuel pump would be prime candidate now.

[kris72079]

Originally Posted by cocobolo95

Fuel pump would be prime candidate now.

Thanks Coco...I will put new one on order today and post back when I have a chance to change it. So you have the trap door access installation link handy?

[kris72079]

Originally Posted by kris72079

Thanks Coco...I will put new one on order today and post back when I have a chance to change it. So you have the trap door access installation link handy?

Nevermind...Found it!
Fuel Pump Replacement on F-Bodies - MEASUREMENTS - Worldisround photo

[kris72079]

Anybody tried the TRE Performance 255LPH High Pressure 343-2 pump? Just ordered one based on cost and the fact that the seller sells and equally compares them to the WalBro pumps. Comments?

[cocobolo95]

The TRE fuel pump is a Chinese made walbro clone. A POS. Do yourself a favor and order the genuine article from a source like Jegs or Summit, and get the genuine article instead of a cheap knock off. The Chinese clones even have welbro inscribed on them, just like the real deal.