I am not sure if this is the right area, but it may be something to do with the tune. I need some help with running issues. I have wired up a ’99 LQ4 into my brother’s off road buggy. The engine is stock with a set of essentially open long tube headers “like almost all the buggy guys run”. I say open headers, but actually it has about a 4-5” long 3” ID straight thru resonator welded to each collector with one of those inverted cone spark arrestors in it. The front O2 sensors are placed in the collectors about 8” or so from the tip of the exhaust. I tried to put them as far up stream as I could, but this is as far as I could go. Due to lack of room I had to do away with the MAF. Since this engine’s original MAF housing included the IAT, I splice into the IAT signal and ground and put a standalone IAT out of a LT1 body style 6 cyl Camaro in it. I checked the resistance across the original IAT and this one at the same temperature and they were of equal values. In doing away with the MAF I had the credible turner, doing the mail order tune, do a speed density tune. I know it is not ever good to do a SD tune not in person, but I needed the VATS cut off so I could test my wiring and the tuner felt VERY confident doing the SD tune mail order since the engine was practically stock. The transmission is a Turbo 400 with a small stall, so I did away with practically all of the transmission wires except for the VSS. I kept it because I read where I needed to add a pulse generator to the Turbo 400 and hook up the VSS so that the PCM would have some kind of signal if the vehicle was moving. I was told not doing so would generate an idle problem so I bought the generator and plugged it up. The fuel system is a 255lph Walbro in line pump and appropriate filters. Besides these things it was a pretty basic tune which included turning off emissions “Rear O2s, EVAP, and EGR”. I am not running any vacuum lines of the engine. The one on the EVAP solenoid and the large one that typically goes to the brake booster are cap. I also plugged the hole into the intake where the EGR originally feed.

Now the problem begins. When I crank the engine it idles extremely rough and dies. Sometimes it will die immediately and other times it will run 30 or 40 seconds. The rpms are sporadic since the engine will almost die then rev up to idle. Sometimes you can rev it up a little, but most of the time it just dies when you attempt to rev it up. The same goes for if you go to drive it, as soon as it gets under any load it dies. I wired up an OBDII port, but when I scan it I cannot find any codes. It is a nice MAC Tools scanner, but it is a bottom of the line basic one.

This is what I have done: I went ahead and replaced the plugs with a fresh set of NGK TR6 plugs gapped to 0.040”. Even though they did not show to be bad I went ahead and temporarily replace the IAC and TPS sensors for used ones off a running truck “I just thought these could very easily be the problem and I could swap them for free”. I have yet to see any difference in run ability with any of these changes. Also the fuel pressure on the rail looked good “I think it was like 55 or 60psi”. It doesn’t really sound like a miss so I do not think it is in the ignition. However any suggestions on what to check there and how?

I would like to admit this was my first attempt at wiring anything like this up, but I feel like I did a very thorough job at it. However I said that to say this, is there anything super obvious I may have screwed up in the wiring that would give these symptoms? I figure the wiring would be more of an, it either runs or doesn’t kind of thing. I am passed frustrated with this so if anyone has any insight please let me know. Any help will be greatly appreciated.
Chase

 

First off...
you have posted this exact same post in 4 sections.....

you need to go delete the other 3... this is the right section to post in... the others are not.


probably unrelated to yoru cold start issue...but..
8" from the tip of the exhaust, is not far enough for the o2 sensor...
there needs to be 18 inches minimum... this wont cause any issue at cold start... but when your vehicle gets up to full temperture and goes into closed loop... it will have some fueling issues at lower rpm speeds...


mail order tunes are usually spotty at best...
there are some guys that get it closer than other... but its still just a guess...
you need to have a local tuner take a look at your tune and take a look at some scan data to see what the problem is...


not finding any codes, usually means that they did not put your car into speed density correctly... without a MAF, you need to see P0101,P0102, or P0103..
if none of those codes exist... then your car will try to use a non existent MAF, and it will react exactly like you are seeing it do
This is most likely your issue....

Find a Local Tuner...who has a reasonable reputation and is willing to provide you with some references...
a lot of guys will charge $50-$100 to do some basic edits...which includes changing DTC's and looking over the tune for potential other issues...
any reputable tuner will know that the MAF has to throw codes for it to go into Speed Density and work correctly.

start there... report back .