I'm out of ideas, guys. (Truck runs like crap no matter what I do).

[ChrisAU]

Yeah, I noticed that too. It's not cracked, it's like an indention, i think i tightened the air cleaner housing too much at one point and it put a dent in it. This MAP is good, though, I pulled it off my brother's suburban which was running beautifully.

But it didn't have the dent in it on your brothers burb? You very well could have some contacts in side that are broken in that thing.

 

[TylerZ281500]

cant autozone test those?

 

[jdyates]

Regardless, I have another one laying around I can swap on.

 

[jdyates]

Also, I picked up a new coolant temp sensor for sh!ts and giggles, since mine is half broken off anyway.

 

[ndians68]

Does it lag at starting, like you have to hold the key for a bit to get it to start? this sounds exactally like what the 88 did year before last, when we put the pump on it ran fine. (yes, we did plugs, wires, cap and rotor and it still ran like crap unitl the pump was changed)

 

[jdyates]

Does it lag at starting, like you have to hold the key for a bit to get it to start? this sounds exactally like what the 88 did year before last, when we put the pump on it ran fine. (yes, we did plugs, wires, cap and rotor and it still ran like crap unitl the pump was changed)

Doesn't lag at all. Fires right up, then runs like **** lol.

Also, I should mention I feel like a complete asshat, I tried taking the old CTS off......while the engine was still hot. A little coolant leaked out, no biggie, but it was hot as hell lmao

 

[great white]

Change the coolant sensor yet?

Any difference?

Still thinking of which way to go next, my ref material won't be at hand for a couple days yet as I'm currently on the road.

Swapping on a different map sensor might be a good idea. The messed up top piece and broken retaining clip had me staring at it in the pic but the ecm should be pointing there (code) if it's bad or dodgy.

Those plug wires are waaaaaay too long also. It won't cause the problem you describe, but it's more resistance than speced and where it's touches the various engine bay parts is a chaff point and possible leakage to ground. they should be a set of "custom fit" ones (meaning: spedic fit for vehicle) and held im standoffs/wire loom holders. At the very least they should touch a minimum amount of places and they shouldn't be able ti shake of whip when the engine runs/ vehicle moves. Spark plug wires are actually pretty sensitive to this type of damage. Make sure you also pull only at the base of rhe boots and not the wires.

I've dealt with a set that worked fine cold but missed like a lean fuel buck when hot or worked hard. Brand new fresh out of the box accel 9mm jobbies. Problem was the conductor had seperated and cold or under light load the spark would jump the gap but when hot/under heavy load it would still jump the gap but had a very reduced/no spark condition in the chamber due to having had jumped one of more gaps in the wire itself.

If you're concerned about it you can remove the wires one by one and meter them. I can't remeber the resistance value per inch/foot, but google should turn it up. Only go through this pita if you have suspicion that the wires may have an open in them since they're new.

The only other thing that catches my eye is the slightly melted wire wrap on the drivers side front. As long as the wire insulation is intact in there it's ok.

Compression numbers say good pistons rings, valves and probably head gaskets.

So now it's spark and fuel we're looking at as probable culprits.

Since the ecm sees nothing, the electronics seem to be non suspect, but electronics are funny things sometimes...

Still mulling a few things over right now...get back to you after a stop, a coffee and some more thought.

Wish I had my books at hand....specific gmt400 tbi stuff is stored on pretty old and dusty shelves in my brain......

 

[TylerZ281500]

knock sensor from what i read will cause similar issues and not throw a code because the computer tries to ignore it. it then bypasses esc. thats what happened on mine. plug knock back in tuned out the egr and what not and it runs just fine.

 

[jdyates]

Haven't changed the coolant sensor yet, the engine didn't cool down enough before I had to go to work (posting from my phone on break). Gonna change it when I get out and hope for the best.

As for the plug wires, I'm away they are way too long, that's why I used separators to tidy them up as best as I could. When it comes to the plug wires, the last set had the same problem I'm having, and so do these, so I'm making the assumption the plugs are fine. Wasn't a problem swapping them, last set had warranty and were only 3 months old.

The other night I climbed under the truck, and the knock sensor wire had gotten pinched when I put my new starter on, so I unplugged it, untangled it, and plugged it back in. However, I didn't have the problem until waaaay after I changed the starter and binded the KS cable, so that also leads me to believe that's not it either.

 

[great white]

Well, the cts is a bit of a hail marry pass at this point but if you've already bought one slap 'er in and see what it does.

The reason i wild guessed it before is if it's sending erroneous data to the ecm it may always be running in cold start mode.

Obviously, it will start fine if it thinks it's cold but will have various running issues when using the cold enrichment tables in the program.

A cts can fail and not set a trouble code. Reason being; it still send data, its just wrong data. Then the ecm can't properly trim the fuel delivery because it always thinks its cold. You can end up dog nuts rich and that just doesn't run right at all.

If memory serves from the old days when i used to mess with tbi, it won't go into closed loop either if it thinks it's still cold. That means no O2 sensor feedback and possibly funky operation.

It should just default to open loop, but computers and electrics are fussy beasts sometimes...

Like i said, wild guess but if you've already bought one.......