zrultima

I just picked up an 2003 Chevrolet Blazer with a 5.3 Swap I have a what I believe is a misfire under medium to heavy acceleration. I had this same issue in my TransAm replacing the O2 sensors fixed it as far as when I was accelerating. The O2 sensors have been replaced on the blazer but it still has the issue.

The following Mods are what I know is done to it.

5.3 from a 03 silverado
Ls1 cam and LS1 Intake manifold from an 98 corvette
Ported TB and Z06 MAf
Cold Air intake
New head gaskets and lifters since previous owner advise it had a slight tick
Stock 4L60E
Base tune with EFI live

When I picked up the car previous owner informed that there was an issue with injector #6 as it was a loose ground but he had fixed it and car ran great when picked up. I can drive down the highway and no missfiring when i want to pass or speed up violently =D it will start to missfire. On idle no missfiring idles fine no stumbling.Any Suggestions

spacemanspif

iTrader: (5)

Have you checked for if it throws a CEL when misfiring? If it does, and its always the same cylinder, start swapping things 1 at a time to see if the misfire moves. Swap plug wires, coils, plugs and injectors. If you do all that and it stays on the same cylinder, you a wiring issue or a something internally is wrong.

If you accelerate slowly up to a fast speed does it still misfire when you get to a certain speed/RPM? Or does it ONLY do it under hard acceleration?

zrultima

Well as far as what I have seeen its when you r getting up to speed its not in any particular RPM butI havent checked it and verified it to see if it s at a certain rpm. I havent checked the CEl since I dont have a scanner and I just picked it up so I havent been able to but I will try once I get the chance

zrultima

Well took the car out for a spin when driving lower rpm the check engine light wont blink but when im accelerating it starts to blink car has alot of power and it d9es not look or feel like its misfiring

zrultima

Scan the truck and only code that came up is P0200 Injector Control...... Any ideas

zrultima

Nothing lol come on

snook

iTrader: (1)

Potential causes of an P0200 code include:
•Open or shorted injector
•Injector low internal resistance (basically an injector that works, but is out of specs)
•Grounded driver circuit
•Open driver circuit
•Driver circuit shorted to voltage
•Wiring harness intermittently shorting against underhood components

This is why I went carbed, don't like chasing my tail in circles with this stuff

zrultima

It just carb seems like I am moving backwards dont want to do that I always seem to run into electrical problems with every car I get I hate it I can take a pic and maybe you guys can pinpoint where things are going wrong. I believe the guy said Injector 6 had a ground that he had fixed since it was causing missfires but I dont see any lose wiring

spacemanspif

iTrader: (5)

Check to see HOW he fixed it and make sure it is a good solid connection. Chase the ground wire back making sure its in tact and has a good engine or body ground (or does the comp control the injector ground to make them fire????????). Chances are that it combines with other grounds but keep tracing until you are sure that everything is ok.

I'd start here considering your harness has a history and someone els' "patch work". Once you are sure everything is good then it is time to move on to other possibilities listed above.

snook

iTrader: (1)

Dont get me wrong, If you have efi, stick with it, I just started from scratch and went carbed. Same power and close mileage if tuned right. It was too simple for me.

zrultima

Well guys last night I clean some lose connectors and sprayed some grounds.... I don't think it fixed it but my gf went ahead and put some 93 octane fuel and we'll now it runs great I will keep everyone updated cell light came off. Snook I I understand I would do carb on a drag car but not a dd

zrultima

Alright Guys it came on again but only while it was on idle when cranked up this morning and while I was stopped at a light..... As i Started driviing light came off no change in performance though still runs like a raped ape lmao

zrultima

Well car doesn't go into overdrive I am thinking since it has a cam it needs a crank relearn how to do it without a scanner?

zrultima

Well abit of an uppdate

Alright so I sprayed it didn't see any arching from wires, took it to my new friend house for just some testing. Well we check wiring 12v from all injector checked grounds and still nothing so we were both at a lost.

Friend checked for +12V @ all injectors and started ohming out the wires going from the injectors to the ecm, also doing the wiggle test to see if any wires showed ground at any point. It all seemed good. I looked to see if any of the harness might be rubbing, but it all looked like fresh tape and was bundled tightely. It's a little close to the passenger exhaust manifold, but didn't look like it was touching.

Just about all GM injectors I've ever worked on works as they get +12v switched voltage on one side and the other side of the circuit is controlled by the ecm. It uses a transistor driver circuit to provide ground to the injector coil in order to "turn on" the injector. Didn't get too far into the wire harness as I don't know what's hiding under the tape.

Next thing will be to ohm out the injectors to make sure they're all reading the same, then unfortunately it'll probably be unwrapping the wiring harness and visually checking all the wires. From some stuff I've seen the wire harness was not done correctly and will most likely need to be redone or at least looked over and corrected in spots.

ls1nova71

iTrader: (4)

Did you ever swap the parts around to see if the problem followed? You're right about the PCM providing ground to the injectors, so the PO saying one injector had a bad ground sounds like a load of crap to me.

Old Geezer

iTrader: (3)

^^^^^ so the PO saying one injector had a bad ground sounds like a load of crap to me.

Exactly what I'm thinking!

zrultima

Yeah that exactly what he said I dont think he really meant to say it that way but when checking all injector plugs we got 12v+ on all off them we check the wiring and everything lookded fine. I havent swaped out any parts since car runs fine but has a rough idle after a certain rpm it feels great. But since I have the code on it wont go into OD

zrultima

Alright guys so I wiggled the injector wiring harness a but moved it away from the valve cover away from the exhaust and we'll the light stopped blinking. I rode it for a bit about 50 miles and the light shutoff I now have over drive and no more rough idle. I believe I found my problem but when checking the harness itself I didn't see any cuts, opening, or expose wire. Blazer runs fine but I would like to get the bottom of this before it happens again

zrultima

I know it's an 03 ecm from the same LM7 but other than that not sure hotwire had it the connector removed and was checking to see if all the wires match up and we'll they all did but what he found odd was the color of the connectors were from the 98-02 L33 when we pulled up on auto tap old version of efi live it came up as an 03. I have my multimeter now =) but I can't stand this cold weather I'm leaving back to Miami on the 18 I just want no issues on the way back so I'm constantly checking

BigEd_72455

iTrader: (7)

I would say that, if you can afford it, look into a complete harness for your application to just straight swap out. Shouldn't take too long to do and would be well worth the peace of mind for long trips and just plain reliability issues being resolved.

One of the site's vendors is having a cyber Monday sale on all kinds of stuff so you may want to call them.

https://ls1tech.com/forums/conversio...nday-sale.html

Would be better than having to pay a wrecker bill to get you back to Florida cause I don't know of too many shops that keep swap harnesses on hand!!