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

 

If it was the O2s it wouldn't act up till the engine was warm and tried to go into closed loop.

I think you need to get some sort of live data scanner on it.

The tune could be botched everyone makes mistakes. I had a very popular tuner send me some tuneS that were so bad that when I backed down the driveway the car couldn't climb back up the 3 feet into the driveway and I had to reflash in the street.

If the tuner I had used had made big mistakes once or twice then it is a mistake, it happened enough that I would say his reputation is FAR better than his ability.

 

That is what I was thinking with the O2s since it has problems on cold start ups. I hope to get a scanner on it Wednesday, but I just figured with something this bad off it would throw a code. Very true on the tuner, if something doesn't show it's head while being scanned Wednesday I will probably see if I can mail it back to the tuner and have him double check everything. Thanks for the input.

 

MAF issue is my bet

 

Is this the magical non existant MAF that the OP is running? Did you miss the part that says he has no MAF?

This is tune related, and like you said, it would be tough to trust a mail order tune when it comes to speed density. SD requires quite a bit of work over a basic MAF tune. It's not as "self-sufficient" because the SD tune is set with certain parameters, and if those parameters are wrong then the thing will not run right. But with a MAF it can correct itself relatively.

I would try and get some sort of scanner in there, especially a wideband.

 

Maybe try the correct forum???

 

Not even a MAF code...?

 

Are u using a MAC TASKMASTER scanner? If so u will be able to read the live data, cuz thats what ur gonna need to do. I also believe this to be a tune issue...my advice would be take it out of SD mode and set up MAF correctly and go from there! SD is a FICKLE BITCH!

 

Check my reply in the PCM Diagnostics and Tuning Forum....

you've posted this thing in 4 different places...
this is not the correct place here.

Will A Moderator please delete the 3 posts of this that are in the wrong places like this one is.

 

Iat doesnt go to ground should be r25 and r57

 

grounding that wire would dump all kind of fuel into your engine

 

the IAT is not his issue...

its completely related to the fact that he has no MAF... and yet he is throwing no MAF codes...
the pcm needs to throw a P0101, P0102, or P0103 to operate properly when there is no MAF...

it will not run right(or at all in most cases) without throwing one of those 3 codes with the MAF physically removed...

it means whoever did his tune set the codes to no error reported... which is the wrong way to do it... so it tried to force use the MAF tables, which dont work without a MAF signal.

you can ground out the IAT or unplug it and the pcm wont care... it will just read an odd IAT value and fueling will be off... it will still run just fine without an IAT...
I've done it on my own car on accident and forgot to re-plug in the IAT after doing some work in the car..LOL

 

could be a bad tps sensor

 

Not without throwing a code....
Its not a bad sensor...

 

You need a scanner to log all the sensors. Thats where to start.

For buggy's like that I tune them OLSD. The 02's will get false readings but thats not your issue right now.

 

grounding the iat will either tell the computer that its either 300 degrees or minus 50 which will dump or cut fuel.. That a quick trick to use nitrous on a 2 bar pcm

 

If there is no MAF DTC then the PCM is still using the MAF (regardless of it being physically present or not).

 

correct...
well.. sort of...
its not still using the MAF...but it will try to use the table... but will have no reference Hz value...
so it will react exactly like he is saying it is doing....
stumble stumble fail...

 

yes.. it will change the fueling....
but it wont change it enough to cause the issue he is having...

IAT plays a very small part on fueling...only a few percent....not enough to cause the issue

I actually drove for a whole week without an IAT sensor plugged in...was tinkering with something under the hood, forgot to plug it back in
never saw any real issues...
had some odd idle behavior sometimes... but it wasnt enough to cause the car to stumble and die

 

My lq4 had a bad wire to the manifold absolute pressure. Idled like the cam was the biggest in the world. Began taking it back apart, and found a loose wire. It never actualy pulled from the plug. But taking the engine apart revealed the wire issue. Before any other expense I would slightly tug each wire, to see if there'd is a loose issue. Could be a cheep fix