Convert to HEI

[joescott]

Hello all. I have a 1987 gmc suburban with 350 tbi. I bought it with a bad rod knock, so I only ran it for a moment when I got it.
After rebuilding the motor, I am getting code 43's and the truck starts running poorly. I have replaced the ESC as well as the knock sensor and the main computer.

My question is this. Can I go to the junkyard, buy an HEI distributor and run a wire to it and bypass computer control of the timing? I know the service engine
soon light will come on, but will this effect anything else?

Thanks in advance
Joe

[HOGDADDY]

I swapped my 86 distributor with a D.U.I. HEI unit from Performance distributors in Tennesee and it originally had a ECM distributor. I would assume the 87 is very similar. Easy swap.

They are nice distributors too many junkyard HEI's have seen better days but you may get lucky also Summit has some cheaper units.

[dammitmitchell]

if a distro fom an 83 with a 305 and the basic smog computer on it..
it works you can have it if it's the right one... just pay shipping

[Desert1957]

The ECM Distributor in an 87 "TBI" does more than just fire the ignition, unless you are going to do a carb/HEI swap I would try to fix what's in there first.

Code 43 is a low voltage code to the ecm or electronic spark , if you own a DVOM I would check all your voltages to the ECM and Distributor. I have seen bad or disconnected ground wires causing low voltage problems setting this code. Clean all your ground wires , don't forget about the engine to body grounds behind the engine. Make sure the alternator is charging and has the proper charging voltage also.

Your choice but for normal driving I would keep my "TBI" setup , but if you are looking for max horsepower or performance a larger carb and HEI is the way to go. Your choice.

Desert

[joescott]

dammitmitchell Thanks for the offer. The idea was to put the "older one wire" Hei alongside my existing tbi system. Truck runs ok but the computer constantly retards the timing to an almost undrivable condition. The more I read, the more Desert1957 seems to be correct. I am going to have to track down and check all those wires! Not that hard really and when done I will know they are all good. The hardest wire to check is the first one! Thanks for all the help guy's.

[Desert1957]

I'm not sure how much you know about setting the timing on a "TBI" setup , but there is a single wire on the firewall , under the brake booster that has to be disconnected to set base timing. if you try and set the timimg without disconnecting this wire the engine will run rough, hesitate and maybe even stall because the timing is that far off. if you need any other help with the wires concerning the Distributor , let me know.

Also the "Knock Sensor" located on the right side of the engine block , near the starter motor is very sensitive to any engine problems , If the sensor detects any abnormal noises / vibrations / even a tapping rocker arm or lifter it freaks out and tells the computer to retard the ignition timing , also a bad sensor will do the same.

Note if you disconnect the sensor it will cause the "Check Engine" light to stay on.

Desert

[joescott]

Desert1957
Thanks again for the assistance. The brown and tan wire did trip me up. Not because I did not use it to set base timing, BUT because it was no longer in the circuit! Seems the PO ran a different set of wires from the ecm to the dist. I found the "new" set and set base timing. HUGE difference, but I still get code 43. I can only assume the wire harness is butchered up someplace else. I will check every wire and will try and repair the original tan/brown wire so as not to confuse anyone else.
Merry Christmas!

Joe