Page 1 of 2 12 LastLast
Results 1 to 15 of 23

Thread: coughing, backfiring or hesitation Gen II Lt1

  1. #1
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14

    coughing, backfiring or hesitation Gen II Lt1

    I have a 95 Camero 350 Gen II LT1 engine installed in my 55 Chevy. It starts & runs well when cold, but when @ operating temperature, it will die in gear. Dropping it in gear with a small increase of RPM usually gets the car moving, but usually after some coughing, backfiring or hesitation. My pre OBD2 ECM is from http://www.psiconversion.com/ Occasionally, the MIL light comes on, but goes off soon after the car is moving OK. I bought the engine used, & I think it may have a performance Cam in it, as it has a somewhat lumpy idle. Could the performance Cam be the cause of this problem or something else? Help!

  2. #2

  3. #3
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    New fuel tank with new fuel pump, new 3/8" steel fuel lines, new fuel pressure regulator, Fresh fuel, new fuel filter, new fuel injectors, new O2 sensors, new plug wires, plugs are not new, but clean & gapped correctly. Has Optspark, so that is an unknown thing, but hard to check. Harness is a 96, with all extra connectors removed. I am an Electrician, so I got diagrams & verified all ECM wiring & connectors. Runs perfectly in open loop.

  4. #4
    Fuel Injected! bybyc5's Avatar
    Join Date
    Feb 2013
    Location
    NE, Tennessee
    Age
    68
    Posts
    73
    Do you have any way to data log and see what is happening?
    Did PSI make a "custom" tune for your application?

    The MIL light coming on should have set a code. Do you have any way to pull codes from the PCM? Have you contacted PSI about this?
    Sorry for so many questions, but looking at this without more information is just guessing. How do you know the motor is going into closed loop?

    The fact that it runs well when cold is a fair indicator that all your wiring and sensors are working, save for the O2 sensors, they are not looked at for fuel control in open loop.

    Data log and pull codes, then post your results. This will help anyone trying to help you.

    The LT1 motor is a really great motor with a lot of potential.
    04 Lightning Pullies n Tune CAI
    96 Formula WS-6 m6 383 LE3-Heads/GM847/N2O/ Ford 9" 4:33/Sus Work/Stickies/TunerProRT
    93 K1500 383 LT1 with Low RPM 4x4 torque cam

  5. #5
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    Thank you for your response & questions. They are giving me some direction to solve this problem. No, I have no idea about the data log or how to get it. I need to learn how to do that. Currently, I have a 16 pin OBD2 plug installed in the engine loom, because the engine, ECM & car I bought was a 96. But, there was no Crankshaft position sensor, so I decided to go with a 94-95 ECM. I told PCIconversion.com about what I didn't want, the application, transmission type, etc. but at this point, I have no idea exactly what they programmed in, or what the trouble code numbers may mean. Because I have a 16 pin OBD2 connector installed, I need to study my diagrams to see which wire I need to ground to see if & what trouble codes it may spit out. I see some posts about O2 distances to exhaust valves. I have medium length headers, so that length is 18"-20". Maybe that is part of this problem. My engine is not new, but is a GM crate engine, very clean inside, so I think it only has a few miles on it. Whoever put this engine in the 96 Camero, it previously had a 3.8 V6, & apparently that guy never could make it run correctly, because it had a 96 loom & a 96 ECM, but NO Crankshaft position sensor. Another possibility that someone suggested to me, is maybe the valves were never adjusted correctly after the performance cam was installed & maybe there is a tight intake valve. I will learn how to get data from the ECM & post it. Thanks guys

  6. #6
    Fuel Injected!
    Join Date
    Oct 2013
    Posts
    1,022
    You need to check the basics first. Plugs, wires, fuel pressure, vacuum leaks, compression etc. You can't fix a mechanical with tuning.

    Also, you need something to read the codes. You can't jumper terminals on the OBDI port to do it.

  7. #7
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    Well, If you had read above, you would see that most everything outside this engine is new! As I have said above, it idles in gear perfectly when cold. I did not mention above how the engine runs at full throttle, but it runs very hard, so if something was wrong with fuel metering, or some type of ignition problem, that is easy to feel & hear, & it would not run strong! I agree, I need to read the codes, if possible, but I was told by PSI that the ECM they sold me could NOT be read by a plug in analyzer & the only way to get trouble codes from their ECM was with the blinking MIL light. I have a 96 ECM, & when I instal it in my 55 Chevy, it will read all sensors with the key on. But, it will only run for 3 seconds, because I do not have a body computer to give me the fuel enable signal. I have on order a small module that will give me the 50 Htz. square wave signal for fuel enable, so when I receive that, I will try using those parts in my 55.

  8. #8
    Fuel Injected!
    Join Date
    Oct 2013
    Posts
    1,022
    Did you swap sides with the O2 sensors? That will cause it to screw-up in closed loop.

    You can easily read the codes with a cable and PC. The flashing CEL will NOT work.

    I wouldn't bother using the 96 PCM since it is hard to find any software that will tune or data log it, but that's just me.

    Except for the running good in open loop vs acting up in closed loop, that lower rpm missing and backfiring is typical of a bad Optispark.

    Don't have anything else to suggest since apparently everything is good.

  9. #9
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    I know I verified the O2 Sensor wiring, & because one side had longer leads to the connector, I doubt if I could have crossed up their signals. The Optispark is high mileage, like all the accessories on my crate engine, so I definitely will locate another one. I've already changed the fuel injectors & alternator because of high mileage. Where can I buy a Cable & Software to read codes with?

  10. #10
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    Sense my last post, I have done more digging. I found out that the PCM I bought from PCIconversion.com is a 1618851, a 94-95 LT1 model or at least what is what the sticker says on the outside! so, I downloaded TunerPro RT & made a $39 donation 2 him. I made an inquiry here on this forum about where 2 buy a cable, but the place they recommended has their web site up for sale! Mark @ TunerPro RT recommended www.moates.net. $80 $EE definition setthere for their cable, but I also need 2 buy Winflash $20 & download the $EE definitions. moates.net states that the PCM I have is MAP sensor based, so that certainly makes sense to me, why my car runs so badly when idling, because of the performance cam & the low vacuum that always accompanies those types of cam shafts. How much time & money will I have to spend to just get data, then how will I know how or what to modify? And, I may never get it to run well, because that PCM uses MAP sensor based software, which I'm sure is not the ideal solution for an engine with a performance cam in it,So I have come up with another alternative to solve this problem. Shitcan that PCM & reinstall the 96 PCM that the donor Camero had in it, along with a VATS Bypass module, and presto, my car now runs normally!

  11. #11
    Fuel Injected! bybyc5's Avatar
    Join Date
    Feb 2013
    Location
    NE, Tennessee
    Age
    68
    Posts
    73
    {quote}"" my car now runs normally! ""

    So did this work for you?
    I am curious how you got a v6 harness and PCM ( the donor car was a V6, correct?) to run your LT1 good, performance cam or not? Or did I misinterpret the posts above?

    A 96 LT1 harness works fine with a 94-95 16188051 PCM plugged into it. The 94-95 16818051 is not looking for a crankshaft position signal, or the post cat O2 sensors either. The knock sensors are different. Those 3 things will not cause the motor to run poorly. The car in my signature below is using a 16188051 PCM with tune work done with TunerPro Rt.

    If you would like some assistance tuning your PCM, this is the best place for that.

    Also, just FYI, the 16188051 IS a Maf sensor using PCM. It has a map sensor as well, for a Baro reading, also different set of tables in the LT1 tune (VE, volumetric efficiency).

    Unless the cam in your LT1 is extreme. The stock 94-95 PCM should at least start and run the motor pretty decently.
    04 Lightning Pullies n Tune CAI
    96 Formula WS-6 m6 383 LE3-Heads/GM847/N2O/ Ford 9" 4:33/Sus Work/Stickies/TunerProRT
    93 K1500 383 LT1 with Low RPM 4x4 torque cam

  12. #12
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    Yes, My car now idles well in gear cold or hot & when the light turns green, no more coughing, sputtering, backfiring or hesitation, it just runs normally with no other changes other then the 96 PCM. I am not sure where U read that I had or was using a V6 engine harness, but the harness I got from the 96 donor Camero definitely has 8 fuel injector connectors & all the other stuff for a V8. I cannot find the moates.net page that had the statement " MAP sensor based", but I actually copied that phrase from a page on their web site! Different knock sensors? well, they don't cost much, I will buy one for a 95 V8. I assume that because my PCM was reprogrammed by PCIconversion.com, they obviously got something wrong! I told them what I would not need, like EGR, AIR, Body module, etc, they would get it right the first time. The only thing I did not know about when I purchased the PCM from PCIconversion.com was that my GM crate 350 engine had a non stock cam. I bought the PCM many months before I got my car running, so I doubt if they will want to make it right.

  13. #13
    Fuel Injected! bybyc5's Avatar
    Join Date
    Feb 2013
    Location
    NE, Tennessee
    Age
    68
    Posts
    73
    I think your better off starting from scratch with the 94-95 16188051 PCM. Software for the 96 PCM is really expensive, and for your application, the 94-95 PCM is an easier one to tune (IMHO).

    So if you download Wintune, and you already have the TunerPro and a cable, your ready to tune. If you want to. The XDF and ADF files you probably already downloaded as well for using TunerPro from Marks site, and there are some at this site as well.

    Did you get the Winflash software? I think you get 30 days trial before you have to buy. If you can read out the 95 PCM bin file and post it. I'm curious what they did or didn't do. You can download a good starter "stock" file from here, or I have some to chose from if you want. Then tune from there.

    Another thing you may already know, the 95 LT1 cars (f-body anyway) all had the 16 pin OBD2 connector inside the car, even though the PCM was OBD1-16188051.
    Also you don't need the module to bypass the anti-theft system, that can be tuned out of the 16188051.

    Sorry I misread one of your posts above.(."Whoever put this engine in the 96 Camero, it previously had a 3.8 V6, & apparently that guy never could make it run correctly, because it had a 96 loom & a 96 ECM")

    If your a bit unclear on how to use the TunerPro software on your LT1, here is a link to a Camaro website that a guy did a really nice tutorial on everything from downloading and installing the software on>>

    http://www.camaroz28.com/forums/comp...torial-759772/

    Hope this helps some.
    04 Lightning Pullies n Tune CAI
    96 Formula WS-6 m6 383 LE3-Heads/GM847/N2O/ Ford 9" 4:33/Sus Work/Stickies/TunerProRT
    93 K1500 383 LT1 with Low RPM 4x4 torque cam

  14. #14
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    Yes, I would welcome some help with this PCM. The first decision I need to make, is which cable I need to buy, as the engine loom is a 96 & has the OBD-2 16 pin connector. moates.net has a cable for the 95 LT1, but will it work with my 96 loom? They say "Looks like OBD2 but it's not". it's @ http://www.moates.net/aldu1-and-cabl....html?cPath=64 I am not sure if they R referring to the OBD-2 connector or something else! Any Ideas about which cable 2 buy?

  15. #15
    Electronic Ignition!
    Join Date
    May 2012
    Age
    80
    Posts
    14
    So, the correct cable to buy is the model with the OBD-2 connector?

Similar Threads

  1. TPI swap backfiring in closed loop
    By pavehawk in forum GM EFI Systems
    Replies: 11
    Last Post: 12-08-2014, 05:54 PM
  2. Lean hesitation with cold engine TBI
    By 92TBIVentura in forum TunerPro Tuning Talk
    Replies: 5
    Last Post: 07-23-2014, 10:11 PM
  3. Replies: 3
    Last Post: 07-28-2012, 05:10 AM
  4. tbi backfiring
    By chevyman_400 in forum GM EFI Systems
    Replies: 12
    Last Post: 04-03-2012, 06:14 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •