99 MC rough idle , backfiring , dying :-/

[montesittinup]

Ok well I got a 99mc with a 3100 in it... Had a lower intake gasket leak n about a year ago I ordered 3400 heads up from milzy for a swap never got around to it so figured now would be the time.... Finally my mechanic got everything on also I put a egr delete on and a PCM from him ... But the new plugs are getting burnt up n the car is running real rough n backfiring when it's started just wondering if anyone has some ideas to throw out there he is lost on what it could be and why :-/ .... Also it's dying on top of rough idle and backfiring. Posted in 3x00swap but no response yet we r going to try. New set of plugs again and put my old PCM back in instead of the one from milzy hoping it might be messed up ... Any ideas plz possibly egr delete causing or ??

[unchained01]

Vacuum leaks. Plug wires backward Is the PCM programmed for the EGR delete. Are you using 3400 intakes ? Or 3100 intakes. ?

[montesittinup]

Using the 3400 intakes and as far as I know the PCM should be programmed for it well as far as I was told lol but we are going to get back to it m a bit try to figure it out ! Thx also was thinking possibly crankshaft sensor ! So hoping she wanna run soon

[unchained01]

yeah thats possible too check the sensor wires also !!

[montesittinup]

Well ran some more tests n plugged up a better scanner everything shows good except the sensor like it shows that it is there but when u crank on it it doesnt work so think we got it narrowed down . Thx

[montesittinup]

Well finally got her back with my 3400 heads n p n p intakes n egr delete n milzy PCM !!! Ended up being a ignition control module and the angle cam sensor wire was melted lol runs a little rough on idle still but that should relearn itself kinda I imagine ?!

[TGP37]

Vacuum leak.

Causes lean condition at idle. Lean has hotter combustion temps but lower exhaust temps. Rich is the other way around. If your burning plugs you are idling hot, lean.

Test the manifold vacuum at idle. As a healthy engine has a healthy vacuum. Should be around 20 inHg. Check the EGR seal.

Unless you have a wild/hot cam, your idle should be smooth.

Bad crankshaft sensor usually kills the engine and prevents any kind of start. Maybe a pop or two at first but that is it. The other crank sensor by the harmonic balancer will not prevent operation. It is used for fine tuning idle as far as I know.


However, if you messed with the crank sensor wires, that could be it. They are sensitive and require 12 twists per foot and do not like EM interferences. If the sensor is wired backwards, you will have a VERY rough start, terrible lopping until it stalls out. Make sure the Crank Sensor wires are correct polarity. I personally wrestled a backwards wired 7xCKP sensor. Did everything you mentioned.