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

 

O2 sensors have to be 18" or more from the end of the exhaust. 18" minimum. Without that it will not idle. I bet that's your problem period .

 

+1

Just went through this on my car when I got it running with just open headers. Soon as I put a midpipe on it the car would run fine. When the O2 sensor is too close to open air it gets exhaust and clean air making the A/F ratio erratic.

 

really? my car drove home fine with open headers. Ten miles. and It would start up and idle fine too, it was just too loud while i was waiting for the y pipe to come in the mail, And i didnt wanna kill o2 sensors.

 

My old lt1 ran open headers for a month with 0 issues.

 

Didn't read everything... Open headers cause some people huge issues, some people 0 issues.

After a while you will burn out your 02 sensors. Some people have idle issues as well.

Clamp/weld an extra foot of pipe onto the headers.

 

Looks like I probable have a few problems, but we just ordered some material and we are going to extended the exhaust so that the O2s are atleast 18" up stream So this shouldn't be a problem in the near future.
However my brother just called and the mechanic with a good scanner has been working on it now. He said the MAP sensor is showing bad and also that the fuel pump is kicking out. This is all second hand, but he said something about I did not have the fuel pump wired into my oil pressure gauge and the computer was telling the pump to shut off since there wasn't an oil pressure signal. I am not real sure what is going on at this point, but I will find out. I simply just wired the fuel pump up to a relay with the fuel pump wire from the computer being the signal to open and close the fuel pump relay. I will post more info as I find out more. Thanks for all the input.

 

I ran my car open headers just the other day and it caused all kinds of problems. It drove down to my friends fine, took off the exhaust, rode it home and it missed anywhere below 2500 rpm terribly. Then I drove it back to my friends and it was the same thing. Left it a couple days and drove it back cold when I turned it off at home it never started again, it killed every plug and filled the oil pan full of gas. We towed it back to my friends, installed my new 4" single system changed the oil and plugs and it ran perfect just like nothing ever happened. Never again will I even risk it running anything open headers. A friend of mine has a stock LT1 car hes ran open headers for a week now without a problem at all.