Stuff a couple of rags under the intake manifold BEFORE cleaning (near the throttle body), to ensure that you don't get a bunch of water in the knock sensors, and don't spray a lot of water near the injectors or where the manifold meets the heads. You can clean that area by hand very carefully if you are worried.
Also, be sure to cover the pulley/bearings and the alternator with tinfoil to prevent them from being degreased.
'99 Firebird: Under the Knife February 2012 GMHTP Street Heat Car
I just washed mine a couple months ago. Used a pressure washer and some simple green.
Pointed the nose down on my incline driveway.
Rinsed it down with the power washer.
Sprayed simple green on the engine and let it sit.
Turned the car on and then re-rinsed with pressure washer.
Then used my air compressor and dried up the excess water.
Car still run great. I'd recommend a pressure washer since it shoots out water at a higher velocity but actually spews out less water...I didn't cover anything. I didnt spend long periods spraying the fuel rails or PCM area either...
ive done it twice...my engine is totally stock looking and not really that dirty but when i clean it...i just spray engine degreaser, let it sit and then spray it off with the hose....i dont hit the alt or the PCM that much but eveything seems to work fine after..
and i spray the **** out of eveything else to get the degreaser outta there.
__________________ 1999 M6 Pewter Trans Am230700miles & counting
TICK TM SNS Stage2 CAM, TSP PRC 2.5 5.3's, wide *** open BORLA, LS7 clutch & Tick Master, SSRA, 104 FTP LID, FAST 92/92, Edelbrock 1 7/8 Stepped LT's+ORY, 25% UD, Chrome TTM's, strano/bilstein package, 3:73's, TA Girdle, BMR relo brackets, LCA's, SFC's & adj TA, Spohn adj PHB, Full NX Wet Kit, Racetronix Fuel Pump/hotwire kit 520hp 560Tq on 150 shot ~TICK TUNE~ NEW #'s coming w/ SD tune & 92/92
i have literally washed probably 2500-3000 cars engine bays. i do mine in my camaro once every couple weeks. having the car pointed downhill works to keep water from sitting in the knock sensors... pressure washers are fine just dont be stupid and sit the spraying something for 5 mins lol. with a pressure washer it doesnt take much to get it clean
__________________ 2001 z28, bolt ons, bolt offs, spray, stripper model, 3225#s a little spray. going for 10.50s bolt ons and spray