Help! What is wrong with my timing?
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New User
Joined: Jan 2005
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Help! What is wrong with my timing?
1986 inline 6 with control module on distribtor. Timing advances at 2000 rpm which I think is normal, but does not go back after rpms drop, causing poor performance. I have set the base timing with spout disconnected. I have replace the MAP sensor also. Also thanks to all those who posted to the forum about timing marks on the inline 6. I was lost without that.
Freshman User
Joined: May 2004
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From: Salem, OR
Might be your TPS sensor sticking if the linkage is messed up in the intake, or it could be that the lobes have worn off your TPS sensor causing it to stay open, if could also be your stator or part of the electronic advance in the distributor.
Freshman User
Joined: May 2004
Posts: 28
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From: Salem, OR
Fixed my timing.
Well I found out what was wrong with mine, mine was advancing all the time and I couldnt get it to go back down, I replaced the module, the coil, the TPS sensor and finally the Stator or PIP setup in the distributor, it was a royal pain in the neck because I had to press the dist. gear off and everything but it fixed the problem, runs like a champ now. If you decide to do this I would HIGHLY recommend buying your part at Knechts, I got it for $21 they wanted around $30+ everywhere else. Good Luck
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New User
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Thanks for the advice. I replaced the whole distributor today and it is still the same. I have measured the tps and replaced about everything else. I will replace the computer next. I stated in another post that the timing goes back to normal if I turn the switch off then on.
Posting Guru
Joined: Apr 2003
Posts: 1,153
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From: Venezuela
Well, it seems to me some clarification will help.
Ignition timing is based on engine RPM and can be advanced based in Vacum at intake manifold. Computer use some pre-programed rutines to control timing using TPS, MAP, ECT and PIP signals.
Iddling at normal operation temperature, computer usually advance ignition timing to 18 - 22º it produce colder engine operation and fuel econnomy.
While cranking, computer receive signal from starter relay and it retard timing around -6º to 0º
If low RPM, low vacum and medium to heavy TPS signal is detected by computer it means a heavy load is been moved so timing is retard around 0 - 4º untill vacum is develop or RPM is increased over 1500
There are a lot of different operation conditions and Computer made calculations for almost everyone. I t seems to me you need make some more tests to be sure your timing is working wrong.
Do the basic test: Disconnect SPOUT connector, setup timing to 15-16º, leave SPOUT disconnected and drive your truck for some days, note if fuel economy improve something driving at city.
Ignition timing is based on engine RPM and can be advanced based in Vacum at intake manifold. Computer use some pre-programed rutines to control timing using TPS, MAP, ECT and PIP signals.
Iddling at normal operation temperature, computer usually advance ignition timing to 18 - 22º it produce colder engine operation and fuel econnomy.
While cranking, computer receive signal from starter relay and it retard timing around -6º to 0º
If low RPM, low vacum and medium to heavy TPS signal is detected by computer it means a heavy load is been moved so timing is retard around 0 - 4º untill vacum is develop or RPM is increased over 1500
There are a lot of different operation conditions and Computer made calculations for almost everyone. I t seems to me you need make some more tests to be sure your timing is working wrong.
Do the basic test: Disconnect SPOUT connector, setup timing to 15-16º, leave SPOUT disconnected and drive your truck for some days, note if fuel economy improve something driving at city.
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Thanks again for the help. Just to get it clear here is what is going on. Timing set to 10 BTDC as (per manufacturer) with SPOUT disconnected. Shut off engine reconnect SPOUT, timing goes to about 18 BTDC. Hard to read marks but I am sure 10 BDTC is marked correctly I cleaned and painted it white. Truck starts and runs pretty good untill the RPM is at 2,000 for more than 2-3 seconds. Then timing jumps to about 5 BTDC and runs terribly until I switch off then on. Then timing goes back to about 18 BTDC. This happens while driving or in neutral. I can watch it with my timing light. I have replace the MAP sensor, cap and rotor,coil,and the whole distributor. I measured the resistance of the TPS and it looked OK. No vacuum advance, only thing I can see left is the computer.
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Posting Guru
Joined: Apr 2003
Posts: 1,153
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From: Venezuela
Never seen that behaviour before... It seems to me computer is ignoring some information and goes to a failsafe ignition mode.
This problem is caused when computer receives not clear information from sensors, remember we are talking about the first generation of EEC computers.
It can be caused by:
1º Defective sensor (TPS, MAP, ECT and pickup coil)
2º Defective connector(s) very comun on old trucks
3º Defective Wiring
Did you get the error codes??? do it, it can help also...
This problem is caused when computer receives not clear information from sensors, remember we are talking about the first generation of EEC computers.
It can be caused by:
1º Defective sensor (TPS, MAP, ECT and pickup coil)
2º Defective connector(s) very comun on old trucks
3º Defective Wiring
Did you get the error codes??? do it, it can help also...
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