engine miss

[kglowacky]

OK. The codes are PO134 and PO154.
Looks like you are on the right track. Did some research. I assume my rear o2 sensors are deleted from ecm. I am thinking of replacing both o2s and fuel filter. Your thoughts. I have for years said my fuel milage has sucked . I wonder if this has something to do with that.

[leegreen]

Bad mileage and bad fuel filter are not obviously connected, replacing the filter won't hurt anything but I have low expectations of a fix from that. Did we ask about idle fuel pressure above in this thread? That needs to be confirmed

Did your mechanic check for real time data from o2 sensors? That is where I'd start, see if they are flatlining or cycling up and down like they should. You don't need expensive scanner for that, just a phone, torque pro app and a Bluetooth OBD2 dongle, that's maybe $50C

I think those codes refer to 'no activity'. if the real time trace shows a flat line and given you are now questioning if it ever ran right then I'd probably start to question if they are wired right, if there are good grounds, if the o2 type matches the ECM and harness, before I dropped the hammer on new ones.

[kglowacky]

The engine has always run great for 4 years Just low gas milage since (12mpg).. Until recently when it started to miss. I can change out the 02s cheaper than I can bring him back. Do you recommend any brand of sensors. It appears the front and back are the same or are they different when buying them.

[leegreen]

12 mpg is not great but hard to judge that not knowing what it is in and how you drive. My '98 suburban 4x4 with less efficient than LS 5.7 TBI got about that around town. my LS swapped Sonoma gets about 15 on my daily commute

Do you still have all 4 sensors? For GM I think they are all the same sensor and Denso is OEM brand. I'd try to get OEM quality but I don't buy enough parts to be recommending brands. I've been stung by junk parts enough that I am starting to think the pick a part auto wrecker is as good a place to buy LS waterpumps and alternators as the local parts place!

I still recommend you get some real time data before trying to fix it with the money hammer. it ran fine until both o2 sensors failed at the same time just does not ring true.

I have not bought this one but 21,000 ratings say this is worth $30 to try https://www.amazon.com/Veepeak-OBDCh...dp/B073XKQQQW/

And tourque pro is only $5 on play store, You will find videos online about how to use it to get a graph of what your O2s are doing

[kglowacky]

I have 2 sensors. One on each exhaust manifold. The cats are gone and the lower sensors removed. Got a text into the guy that set up my ecm to confirm he only deleted the rear sensors .
Looks like from my research if I need to buy 02 sensor's they are two different part numbers. Both say upstream position. The Denso part #s are
Left 234-4025
right 234-4087
5.7 :LS1 out of a 2002 Firebird Trans Am

Trying to confirm there are different sensors based on each side, seems I can get whatever answer I want. Only thing I can think is they changed parts numbers at some point. 4087

Looks like 4025 was replaced by 4087.

[A1971Blazer]

Originally Posted by kglowacky

I have 2 sensors. One on each exhaust manifold. The cats are gone and the lower sensors removed. Got a text into the guy that set up my ecm to confirm he only deleted the rear sensors .
Looks like from my research if I need to buy 02 sensor's they are two different part numbers. Both say upstream position. The Denso part #s are
Left 234-4025
right 234-4087
5.7 :LS1 out of a 2002 Firebird Trans Am

Trying to confirm there are different sensors based on each side, seems I can get whatever answer I want. Only thing I can think is they changed parts numbers at some point. 4087

Looks like 4025 was replaced by 4087.

I think the only difference is the length of the pigtail so that it reaches the factory connector location.
I bought two different part numbers for my LS1 (from a 2002 TransAm) they were identical except for the length of the wires.

[Dead Parrot]

Make sure all the vacuum hoses are still in good shape and connected where they are supposed to go. A vacuum leak can cause a miss in one or two cylinders. Might also explain the O2 faults by causing the mix to go lean. Don't overlook something like a brake booster that has developed a leak. A booster can still provide boost while leaking vacuum.

Possible a mouse did a quick chew and run on a few hoses.

[leegreen]

vacuum leak might show up in long term fuel trims or since this should be a DBC throttle body, as IAC being commanded to zero by computer. Or surging idle if it is bad enough leak.*

2 dead or unconnected O2s probably just put it into open loop with bad mileage.

weak fuel pressure could account for a random missfire or even a cylinder specific missfire if there is one weaker injector spring. There are no reports of checking fuel pressure in this thread.

A scanner and fuel pressure tester costs less than one new O2 and you can probably get them overnighted to your door. We are just guessing without checking.

My guess right now is the O2 issue is not the cause of missfire



*bad idle....if either computer is not know for sure to be from a drive by cable vehicle is it worth checking to make sure the IAC driver chip is present on the board. Some DBW computers don't have them, some do. but this will not be source of random missfire off idle, at least I don't think it would

[kglowacky]

its drive by cable. factory set up

[kglowacky]

well changed 02 sensors. no help., At cold seems to run pretty normal. As its warns up it starts to miss somewhat. Then get it up to 50 and the truck starts missing so bad feels like a bad tire. (I checked, tires are good, LOL) Then once warned up misses all the time.
I'm looking for someone in North Houston area that can fix it. Thinking a street rodder is what I need. Anyone suggests anyone. Going to see an old junkyard friend that sells a lot of these LS1s and see who he recommends. Tired of trying on my own and don't want to start buying parts or tools I'll never use again.
I do want to say I am over 65 years old and so disappointed in these so-called new mechanics. They have no skill set or understanding on how to trouble shoot anything not on a computer scan. I guess I missed my calling on when I was born. I know I could figure this out with the correct tools but I just want it fixed so I can enjoy it.
thanks everyone for your thoughts on the thread it helps to have someone to bounce ideas off of.

[LS short box]

I would go over to LS1tech.com and ask about tuners in the Houston area. Got to be more than one.
Or a quick internet search looking for LS tuners in the Houston area.

[leegreen]

Any general mechanic shop that can't fix 20 year old GM V8 tech has really missed the boat. You exactly want someone that has a computer, a tool box and makes his living making daily drivers run right.
Statistically that implies you don't want a hot rod shop that maybe builds a handful of cars a year, or a tuning shop that tweaks bolt on stuff with a dyno, you don't want a place with shiny floors and a line of new cars waiting for an oil change and wash.
You want the place one block off the main drag where the rent is cheaper with work trucks waiting to be fixed and guys hustling around making a living. "Family run, 4th generation" would be a good indicator

[kglowacky]

Love it. Now i'll get to work finding one.

[A1971Blazer]

I had a couple of issues with my LS1 when I swapped it in to my '67

First was a random misfire on every cylinder on the driver side. I replaced the coil harnesses on both sides after I figured out it was the connector plug to the coil harness.

Next was a MAF issue. When I connected the scan tool there was no reading for the MAF sensor. I tried cleaning it, still nothing. I replaced it, still nothing.

So as it was running I wiggled the connector and immediately it began to read on the scanner. (should have done that first).

As you might guess, it was a bad connection. I was able to tweak the pins in the connector, that fixed it.
So, all that to say, check the connections to the coil packs and other suspect components that would cause the miss issue.

I had already bought the HPtuner package mainly for the reason you expressed, finding someone that could troubleshoot and repair the problem is difficult and expensive.
For me it has paid off to have it.
I have modified some setting on my engine and transmission, and also done some for my friends.
The way I see/justify it is that it's just another necessary tool.
Anyway, good luck with it!

[kglowacky]

truck goes in on Monday to a shop I used for 30 plus years when my body shop had a major electrical or not so simple problem. He always found and fixed every job. Honestly forgot he was still in business. Talked to him, his sons help him run it now BUT he promised me he will be there to get it fixed, Off the beaten path but I am extremely happy to take it there. His son has 4 or 5 ls1 engine swaps working on right now. I am pumped. Don't know why I didn't think of him 2 months ago.

[leegreen]

was a fix found? curious

[kglowacky]

went there yesterday. They say Yes but I am having them find the leak in my a/c so I haven't driven it yet. But they say it runs great. Offered to buy it. I gave him my price, he said a fair price for what I have. Now as far as the fix. They say no codes, but it had 2 bad spark plug wires and therefor 2 bad plugs. Replaced all the plugs and wires. I really am speechless as the 1st two mechanics didn't find this. I asked why no codes he says a lot of times when the ECM gets reprogramed or whatever they do to them when they remove vats, they do something to them that sometimes stops the ecm from picking up certain codes. Not sure I understand all that but its fixed and that's what I needed. will update one more time when I get it home and drive it.

[biketopia]

When a stock ECU is retuned, the tuner can block certain codes from illuminating the CEL, or even reporting at all. It's typically just the EVAP type codes and Rear O2's turned off though. I have also seen it, mainly on Fords, they missfire but don't tell on them selves directly but give a different code that makes the trouble shooting more difficult.

[Joyridin]

I had a tuner recently that shut off just about everything. The one spark plug wire was not on the plug correctly and it would run weird going down the road. No codes.

I found the problem and turned on the codes. Crap tune sent the whole car into a meltdown. I had 15 codes appear after turning them back on.

[leegreen]

someone selling 'unlocked' ECUs with bottom feeding used car lot tune designed to hide problems

or 'tuners' that just know how to copy and paste tunes from the forums and figure the tune that claims the most HP is the one everyone wants

[AussieinNC]

I have enjoyed reading this post immensely, sorry I could not add my 2 cents worth until today as life has been throwing hand grenades just about every week.

I get the feeling that sometimes folk overlook the obvious and go searching and relying on the computer etc.

Now this is not a downer on the modern diagnostic tools available, rather my observations from the thread.

1/ Original donor vehicle was at least 20 years old...how old were the plugs and leads and coils? Original issue? First stop, swap out plugs, coils and wires with new, even if they are Amazon quality.

2/ While you have the plugs out run a compression test to ensure the engine doesnt have a valve or cam issue.

3/ Check all grounds on every coil pack...remember, these coils are all 12 volt on with engine not running, the ground is removed causing the coil to fire...bad ground and they may fire ok when cold but not when engine is hot. Always add an additional heavy ground wire between engine and chassis.

4/ Vacuum leaks can influence the trim tune in the ecu, just like on a carbed engine...biggest issue I have found is the vacuum brake line becoming oil contaminated and breaking down. Dont even get me started on the gruel we laughingly refer to as gas!

5/ IMHO, when tuning an ecu, the tuner removing the code alerts for misfires and fuel injector codes is totally un-necessary. it shows an inexperienced tuner who cares less about the product and more about the quick turn over of the retune process.

Glad you are moving forward with the repairs, it can be frustrating I know when you are trying your hardest and not getting the results.

Post up your results so we can see what was final diagnosis and corrections etc.

Bill

[kglowacky]

UPDATE: Just picked up truck. Drove it home over 25 miles. ran great, before i knew it I looked down running 70 plus. Ac blew really cold. Engine temp in middle of gauges. Only slight issue and maybe being way to cautious I think at idle my volts will drop below 13 on gauge when a/c on. I would say no lower than 11 as the org gauge shows but the minute you move the volts go to 13 plus. If I don't run a/c it is at 13 plus at idle. Both my fans turn on with a/c on. In Houston I am protecting the engine temp with our heat. Overall, very very happy with mechanic work. As far as when I transplanted motor. For sure new plugs but no wires. Engine seller said 75k on motor ecm tuner said 175k on ecm. LOL who to believe. Thanks everyone.

[AussieinNC]

So happy you got it all sorted out and can start enjoying the truck.

Re volts....maybe add a newer high amperage alternator to the system. Also remember the wiring in the truck may be original and not accustomed to higher amperages.

Re ecm and mileage....there is no way to know the ecm supplied was the original to the car or not....

just enjoy your ride sir...