351 '1990 EFI

<table style="border-collapse: collapse;" border="1" bordercolor="#111111" cellpadding="3" cellspacing="0"><tbody><tr><td valign="top">18

</td> <td valign="top">(KOER)</td> <td valign="top">Check base timing & advance function. (Mem) Ignition TACH signal erratic.</td></tr></tbody></table>

Im getting this code 18 now starting yesterday. (What does the Mem mean)I keep having problems with my timing. When the truck runs crappy i change the timing to somewhere between 10 and 20 BTC(spout pulled) till it runs right then it runs really great for a day or 2. Then it sucks again and unless i find the right timing(which is nearly impossible and takes a lot fo time. The spout is doing its job cause if its not connected it runs crappier.

When i first bought a timing light 2 years ago and checked it it was at 20BTC(yes I pulled the spout) and in general it runs best at that but i still dont feel thats right right. When i tried to turn the distributor the previous owner cemnet glued it on i believe to stop oil leak from the base ,since when i finally did remove it the O-ring was completely gone. I put in another distributor but still got the old one.

I dont know what to do next? There are times the truck runs awesome and feels like when i got it 5 years ago and my gas mileage is up to 16mpg highway. Most times Im stuck at 10mgp city which isnt bad considering the age but it just aint running right.

Ive changed the TFI module but it didnt seem to have any improvement

Any ideas?.

Would a loose timing chain cause this problem.??

Thanks

 

The "mem" (short for memory) is the "last known timing advance" parameter set by the computer the last time the engine was running. If SPOUT signal was erratic during that time, code 18 will trigger. SPOUT signal can be affected by the connector, the TFI module, or any of the connections/wiring between them.

On a side note 20 BTDC is way too much. 8-12 BTDC is the norm but it should ONLY be set with the SPOUT removed AND the engine at full operating temp. Otherwise the advance will be off because the computer "assumes operating temp" when adjusting the timing. The exact base timing setting is listed on the CATALYST decal under the hood. Set according to the decal before using any other setting.

 

THanks greystreak. I didnt know the engine had to be at operating temperature. I was setting it at cold with the spout connectore removed . I see Haynes also has checks for each connector wire to the TFI module so Ill check out the voltages/resistances and "wiggle test " the wires.