Help diagnose intake vacuum leak...

[Morkai]

I've been chasing a problem causing my engine to idle and cruise rough for a while now. All started after putting in 50's with T+ and a cam swap.

I've replaced or check about everything but the intake gasket itself. (I did the carb cleaner check on the topside) I figured it was the 50's, because they wanted to run rich with low BLMs on me. Tried with and w/o the T+ & extender also with a PTE chip. Put the stock maf back in during that.

I finally decided they might need a good clean&flow. I took them out and put my old stockers back in to test. Still rough, actully been getting rougher it seems, cutting off all the time. I figured all that was from fouled plugs, but no. Stock injectors doing it to, BLMs are ok on it as long as I stay out of the throttle, plugs look good.

I checked the outside header temps, all were around 500* cept for #6 was about 100* less. that plug is cleaner too. Swapped that plug for a new one, and put the noid light on the injector, everything seems fine.

My main question is this.... Could a vacuum leak from under the intake on that port cause a low exh temp?? I would think it would be hotter if it's running lean, but I guess if it's so lean it's not combusting good it might be cold. Any ideas much appreciated.

 

[Morkai]

more info

Guess I'll be thorough, here's what I remember doing so far:

New plugs, over and over, swapped the wires with old set, took each off individually and used my spark gap tester, all spark looked good and hot. All seemed to have an effect when disconnected.

New module, newish accel coil pack, cam sensor is not 180 out. Tried two 50# chips (ext & pte) with and without the T+ and ls1 maf.

Crank sensor was new before cam swap. Tried different fuel pressures...

Sprayed anything and everything with carb cleaner on the topend for leaks. Also replaced the EGR.

About the only thing I think I haven't done is replace the intake gasket.

Oh, and I miced the cam lobe lifts, all within .002-003" of spec at the pushrod.

 

[Morkai]

gasket

I pulled the intake. I can't see any signs it wasn't sealing good.

I did, however, notice something odd about my injector harness. The plugs are numbered 2,6,4 in that order on the passenger side. From what I can tell, it's still strapped to the rail with the original tie straps. If this is the problem, why wouldn't it have surfaced in the past?

Anyone know what pins are what on the connector so that I can trace them to see if it's just numbered wrong??

 

[T4Texas]

go to http://www.vortexbuicks-etc.com/

click the troubleshooting link in the L/H column,

then the link at the top R/H corner that says "Fuel Pump/Fuel Injector Circuitry"

HTH, good luck chasing your gremlin

 

[soundguy]

if the injectors are numbered 2,6,4 in that order that is most likely your prob. Ya got 2 cylinders that are getting fuel at the wrong times and is probably getting it on the exhaust stroke which would cause a lean mix status. Number 6 should be the shortest wire for that side. Check the lengths and put the shortest as number 6. Someone may have relabled them wrong in the past.

 

[Morkai]

wiring

That's just it, I'm pretty sure this is the factory wiring that has been untouched, I know it's not changed since I've worked on it. Why would it not have had problems before?

#6 has a black wire with red stripe, #4 has a black with looks like yellow, but they're labeled opposite on the connector. Looking at the diagram, they are wrong. Blk/red should be 4 and is labeled as such, but on #6 injector. It looks to me like it's been that way since the factory, why wouldn't it have run bad before? Would the larger cam bring out the problem in injector timing?

I sure hope this is my issue...

 

[Morkai]

Well, I put a new intake gasket on, sealed it real good. Put it all back together with the stock injectors and swapped the 4 & 6 wires so that they were correct. Still missing like crazy. I give up....about the only thing I haven't done is buy new injectors.