97 vortek 7.4 ignition timing question

Hopefully someone has encountered this problem before and can help me.I have a 97 3500 wrecker that has the 454.Since I bought the truck 8 monthes ago it hasnt had much power and only gets around 8 mpg but it does weight 10K lbs.Last week I was towing a car up a hill and the engine was working hard,then it started running like crap.It feels and sounds like it is running on 7 cylinders.I replaced the plugs wires cap rotorcoil module,fuel filter.The only thing left to change is the distributor which I probably will.All 8 injectors are only 6 months old but I removed and cleaned them just incase and they seem to be working fine.I did a compression test and all cylinders has 135 psi except one has 140 and one has 125 so that not that bad.I did a back pressure test and it only has 1.5 psi like it should.Now heres the strange part.I hooked up my scanner and test drove it today,the timing is at 26 degrees at idel and as soon as I touch the peddle it drops down to as low as 2 degrees.That explains the loss of power and bad gas mileage (5-6 mpg right now).The air fuel is mixture is right where it should be 14.7.The only codes are (po161 b h02s heater circut bank 2) and (po172 b fuel trim system rich bank 1)If anyone has any ideas or has experienced this I would really appreciate any help.Thanks

Since you have a scanner, check the ECT and IAT temps when the vehicle is cold and see if they are close to being correct. As far as timing the vehicle, it can only be done if your scanner can read the cam retard value.

The P0161 cannot cause the problem. I would swap the oxygen sensors that are closest to the motor(pre-cat sensors) just to see if the P0172 changes to a P0175-bank 2 rich.

Anything in the misfire history, you may also be able to read knock retard which could drop your timing. Use the scanner to monitor the throttle position sensor voltage while slowly pushing on the pedal- watch for dead spots, the reading should slowly and steadily increase as you slowly push on the pedal. Fuel pressure should be 56-62 psi, key on and engine off and should hold pressure when the fuel pump stops

good luck

Hey,Thank you so much for your response and your help.You are right,the scanner does read knock retard,it was retarding it I believe 0-5 degrees.Today I unpluged the connector to the knock sensor to see it that was bad.I didnt see any codes in missfire history but I should probably check again.I will check the temp readings,I tend to think that iven if the sensors were bad they wouldnt make it run as bad as it does though.I did check the tps sensor but I only checked it as fas as it read 0% at idle and as I pressed the peddle it increased and it was at 100% at wot.I will check the voltage for dead spots,I didnt pay any attention to the voltage simply because I wasnt sure what it should read anyways.What about the timing?I know just enough about the newer stuff to get by but on the older cars timing is usually around 10 degrees at idle and it gradually advances to around 36-38 degrees at wot.My scanner is showing the opposite.Thats not right is it?

Cam retard should be 0 degrees. If it varies a lot I would check the distributor assembly over to see if it has a bad gear and/or bushing and compare the tach readings on the scantool to the tach, a bad crankshaft position sensor will sometimes give the PCM bad info on engine rpms.

As far as ignition timing(I have a 305), it will read in the 20's at idle, I think down to 12 at WOT and it will read 30+ during light throttle at 40+ mph

Huh,thats interesting,so I guess its not abnormal that the timing is going lower instead of advancing like im use to.I dont completelly understand the cam retard but I checked it today and it was at 8 degrees.Tomorrow I will plug the knock sensor back in and see if its the same.If so I will buy a distributor and see what happens.I drove it today with the knock sensor disconnected and it still runs like crap but does run better.The timing only dropped to around 14.

The cam retard on your scanner should show 0 +or- 2degrees. Those distributors are junk on these engines, after time the gear wears as also the bushing inside wears out, causing a fluctuation in cam retard. The pcm controls ignition timing not the distributor. The cam sensor in the distributor works with the crank sensor. Hope that helps.

Hey Thank you for the help.My truck only has 20k on the engine but I believe the distributor is original and the truck has 196k on it so I plan to go buy one in a day or so.Its only 90.00 at autozone so I figure Im this far into it I should replace that and at least the the complete ignition system will be new and I can rule that out.It doesnt seem to have any play but who knows.I did consider the pcm or the cam position sensor but its hard because the scanner isnt picking up any codes other than the 2 I listed and I know there not making it run like this.Its been -20 to 10 derees here so I probably wont get to the distributor until next week when it warms back up to the balmy 20's.Once I swap it I will check back in.Any other ides or advice in the mean time is appreciated.Thanks

Only $90 at Autozone, for my truck its $170 for a reman or over $300 for a new one according to their website

Yeah I was surprised too.I think that 170.00 your looking at is without the core because I went down today and ordered it (it will be in Wednesday)and it cost me 160.00 but there it a 60.00 dollar core so it will end up being 90.00 something when I bring in the old one.I sure do hope that cures the problem.

Well I can now rule out the distributor.It still shakes while accelerating and has no power.HELP!!!!!!