yorkshirespud

I am rebuilding the motor in my 1987 Chevy R30 1 ton 454 dually crewcab pickup, which is the first year of TBI in trucks, and I'm very confused about the knock sensor!!

The knock sensor in this block should be at the bottom of the block on the left hand side (looking from the front) at the front corner. On my engine, there is a blanking bolt in its place. No problem I thought, I'll get a replacement knock sensor, and wire it in where it should be.

I then consulted the full wiring diagram for the engine, I have a full dealer large sprial set of wiring diagrams, including all motor wiring. The diagrams list all the ECU connections, MAP, TPS, Oxygen sensor, but, guess what, no Knock Sensor is in the diagram either!!!!

My truck definitely has the 1227747 ECU, and TBI injectors etc, MAP sensor, 02 sensor etc etc, but now I'm confused about the knock sensor. Does the 1987 TBI not have one?? There is no wiring for one, and a blanking stud in the block.

Can anybody shed any light on this???

Thanks.

yorkshirespud

To clarify what I'm asking: is it correct that early versions of the '7747 implementation do purposefully not include an ESC module and knock sensor, i.e. there is no retarding, and the only feedback loop is the O2 sensor??

RBob

iTrader: (1)

Yes, a lot of the BBC trucks did not run a knock sensor. Also, quite a few ran open loop idle.

RBob.

yorkshirespud

RBob! Thanks for your input, at least I know I'm not losing my marbles. I had long assumed that all ECU controlled motors ran with knock sensors, so it was a bit of a shock when I realised this week that there is no harness wiring intended for a knock sensor on my truck. I've rebuilt the motor with aluminium hi-comp heads, more aggresive cam etc, and actualy the lack of knock sensor removes the worry about the gear driven cam gear I have also installed.

Ok then, onto the main question: without knock retardation, how do I make sure I don't cook my new motor while tuning it?!? The only monitor I will have available is O2. Thankfully, I am also installing a WideBandCommander O2 sensor and logger in the refit. That now seems a wise move as it will be the only feedback data I'll have?

Presumably the stock big block motors, being originally detuned by GM quite a lot, and the piddly stock static advance (4 deg) meant knocking was never considered to be a factor to worry about?

I have an Ostrich and laptop ready to go, so hopefully mixed with the WideBandCommander I should be able to tune this thing. I should also note that previous to the rebuild, I already installed an Edelbrock MFPI converstion intake manifold, which 'converts' the (dual) point TBI injection into multi-point (though NOT sequential) injection. I have replaced the 8 injectors in the Edelbrock manifold with larger ones, and already have a 45psi fuel pressure pump installed as per the Edelbrock conversion. I'm aiming for 1hp/cu, abour 450hp.

Any advice or input appreciated!!

Fast355

iTrader: (2)

I have a NOS GM TBI harness for a C60 Series truck (366 or 427 Tall Deck BBC) that uses the 7747 style ECM connection and wiring. It is sans an ESC module, Knock sensor connector, and knock sensor wiring. The harness also has Governor wiring and connectors in it. Finally it was OEM with a heated O2 sensor and has weird TBI connectors on it (the same the 2.5 I4s)

fastcars

The 454 in my car originally came from an '89 suburban.
I pulled the engine and did the swap myself. My motor was TBI controlled with the 7747 ECM and did not have a knock sensor or any of the wiring for it or the module.
The purpose of the knock sensor was to compensate for a bad tank of gas not as a tuning tool to correct excessive timing programmed into the ECM. Although I'm sure there are people doing it as well as other reasons for doing it.
With a bit of knowledge, some experience and your ears and eyes you should be able to tune that thing without a knock sensor. Millions of engines have been tuned in the past and even today without the use of a knock sensor.

By the way, your set up sounds really cool. I like it!
I converted my 454 from TBI to a late model Vortec multi-port set-up. I'm using a 7730 ECM to control it. Still tuning it with the old fashioned chip burning method. I should really step up to an emulator! Oh, and I still don't have a knock sensor.
Good luck.

FASTCARS

yorkshirespud

Thanks for the sanity check guys, I'd just make the wrong assumption that knock sensors were the norm! Obviously I do have the correct setup without any butchered wires, which is what I wanted to check.

BTW, you can check out some rebuild pictures at

http://fullsizechevy.com/forums/showthread.php?t=242203

Edit: some later pics also at:

http://www.aacint.com/forum/m_120867.../tm.htm#120867

http://www.aacint.com/forum/m_122045.../tm.htm#122045

for the interested.

One more thing then, seeing as my block does have the mounting point for a knock sensor, how does the following sound: One of the features of the WideBandCommander O2 logger I'm also installing it that it has a couple of spare auxillary inputs (expected 5V range, like most automotive sensors/electronics) that can also be logged, along with the O2 readings, RPM (it has a tach input), etc. If I could get hold of a standalone ESC module, then potentially I could hook up a knock sensor installed in the correct place in the block, and be able to at least LOG knock counts, even if they woudn't actually retard the egnine, if the output from the ESC module was used as a WidebandCommander auxillary input line.

Any thoughts?

Cheers

zapeee

I have just put the engine from my 1988 k3500 4 speed pickup into a 1995 yukon 5-speed 2-door. I bought the pickup new, and vaguely remember seeing the knock sensor lead hanging down near the starter (every time i changed the oil) before i sold the truck in 1991. I repurchased the truck in 2005 and pulled the motor and rebuilt it. when i got the block back from the machinist, i couldnt locate the stock knock sensor location. the only thing that looks likely is in front of the starter, but is blocked by the factory stock dipstick tube. nothing else is threaded right.
GM, Napa, and other parts stores say there is a knock sensor for this year and engine, but GM tells me that the sensor goes on the drivers side, which is incorrect as there is an oil gallery there, and other sources put it under the intake manifold, which is also incorrect. i kind of believe it never had one, but want to use one so i can run cheap gas without worrying about it.
the factory owner's manual for the truck talks about pinging in a wishy-washy corporate way, saying it's normal.
the pickup came with a 7747 ecu and an AFTA chip- probably not many people hopping up one ton stick shift trucks, so no bin file to be found.
i cant seem to get it to stop running rich without creating other issues. the only changes i made is i increased the compression from 8.2 to 8.69, but also put in a very radical cam not recommended for EFI, emissions, or the 5000 lb truck it's in (comp cams cca-cl11-239-3). it idles, makes great power, and seems to run well but the BLM is seldom above 120. i can get it to run closer to 128, but consistency goes out the window. mileage in the yukon with better gearing and less weight is worse than in the pickup.

in order to get my truck to start i had advance the base timing around alot(obviously cam causing this). it just wouldnt start at 4 and hesitated horrendously until i brought the timing up to where it is now. note the program is set for about 41.9 degrees max advance. you need to set the base timing in the program where you have it set so you dont melt your pistons. 42 degrees of full advance is the absolute limit and you definitely will have problems if you have more advance than that. (if i didnt change mine it would be able to reach 55-60 degrees)

i hope some of this helps, please let me know if you figure it out. i gotta figure we would both be better off with a working knock sensor. i now have about 4000 miles on my new motor without one.

Drumer919

If your going to do all you may as well just add it to the ECM, just need to wire it all in and turn it on in the tune.

Oh and Zapeee, why not leave base timing the same and just add startup spark in the tune? Sounds like you have alot of tuning to do everywhere though.