Hi all I am relatively new to the forum, however I have been searching and reading up on the ignition setup on my 96 E-250 Service van.
The vehicle:
96 E-250
4.9L Inline 6
C-6 Trans
2wd Cargo van
194,000 kilometers (121,000 miles)
Base timing ~12degrees
The problem is that I have very low ignition advance coming out of the PCM when the motor is under load. This is causing poor acceleration, and single digit fuel mileage. I also don't drive it that hard haha.

At idle the advance is normal approx 18 degrees, and varies up and down as it should to fine tune idle speed. I have verified this with my timing light as well as the data stream on my obdII scanner. With the spout unplugged I have a fairly solid 12 degrees of base timing. At cruising speeds in town however I have approx 23 degrees(based on data stream) and under acceleration typically around 5 degrees. At WOT it goes to an incredible 0.5 degrees and is gutless. The van currently has no error codes present. I recently changed the rear upstream O2 sensor, and I plan on changing the front upstream sensor as soon as the penetrating oil has some time to soak in. I measured the knock sensor output with my dmm and get a 2.5vdc bias voltage, and 0 vac at the sensor even at WOT. Also the motor has no audible knock under any operating conditions, and runs very smooth.

I am currently at a loss as to how to continue, if anyone has any suggestions or questions please let me know.

Thanks in advance, haha

 

I had this same problem with my 96 van's 351. The base timing was supposed to be 10BTC, but it was showing 15-16 while idling getting the readings thru the scanner. I loosened the distributor and played with the timing setting while it was running til it showed 10*, I then locked it down and it's run great ever since. I suspect yours is doing the same as mine. I actually had to retard the distributor to get the base timing idling down to 10*. My son said it was likely advanced too far to begin with and the computer was not able to retard it enough on it's own. My total timing now is in the high twenties, reving it to 3-4000 rpms in neutral in the driveway.

 

Hmm interesting, did you have the spout disconnected when you set it to 10 degrees? Does your obd scanner read the same timing as your timing light now?

Also a quick update, I recorded the knock sensor with a mini tape recorder. Then traced the playback through a lab scope. There is a hugh amount of noise coming through this sensor.

So in short my multimeter was lying to me there was ac voltage going into the ks input at the pcm. I have temporarly "filtered" this noise out with a 1mfd capacitor, and the timing increased by approx 6 degrees across the entire wot range. So at my 2000rpm wot test I have now an indicated 6.5 degrees instead of the previous 0.5 degrees.

This 6.5 degrees still seems like very low timing to me. Does anyone have a reference they have measured with their obd scanner for the 96 4.9l?

baddad457 do you know what your wot timing was at roughly 2000 rpm on the 351?

THANKS

 

When I first disconnected the spout, the engine started to stall, then recovered. Next time I unplugged it, no effect was observed. I cannot use a timing light to check the timing, too much "stuff" in the sight path to do so. If your knock sensor is registering noise, then the PCM would pull back on the timing (retard) with no noise, it'll advance it. So if your timing is advanced too far, then it's creating the knocking, forcing the PCM to pull back the timing. Try setting the base timing using the code reader instead of the timing light. This is what I did. Does your's have a crankshaft position sensor ? Mine does.

 

Thanks for the info. Yes I do have the crankshaft position sensor. I tried your suggestion however I did use a timing light. I was able to get to some pretty crazy advance (like an extra 40degrees) and the computer would eventually just lower the idle air valve position and bring the timing from 10btdc up to roughly 16-18(these are just indicated values from the data stream). The data stream readout of timing seems to be what the spout is sending out, it isn't an input from the crank trigger wheel I don't think.

After reading this thread, I'm doubting my tdc mark a little bit haha.
Timing marks?????? - Ford Truck Enthusiasts Forums

I set the timing a few degrees advanced from where I was before and it seems to run a little better, no knock, but I haven't done any hard wot pulls yet. The scanner data stream is contently reading out all the same advance numbers as the previous post which seems like odd numbers to me...

If I have time tomorrow I may throw my dial indicator in the #1 hole and make sure my mark is indeed tdc.

 

Mine acted similarly, I had to play with the settings (distributor) until I was able to "see" 10*BTC (initially) then locked it down. It would still bump the timing up a bit after the initial 10* was seen. The proof though was in the driving afterwards. Night and day difference.

 

So a quick update...

I haven't put my dial indicator in the motor as I don't think it's necessary yet at this point. I verified the timing marks on the damper, and I don't think it's slipped at all as it's a 3 month old oem replacement.

The base timing is set to 10 degrees based on the passenger side marks. With the spout reconnected it advances as I think is normal to "fine tune" idle speed with the ignition timing. However, it seems as though the timing is running in some sort of limp mode map/curve.

At idle timing modulates from 10 - 24 degrees to fine tune idle speed. This is indicated by scanner as well as observed with timing light.
At light cruise in town I have roughly 23 degrees (indicated by scanner)
At WOT & 2000rpm I have 7.5 degrees (indicated by scanner)
Also no error codes present except when I disconnect spout connector...

All these numbers seem really low to me. Is there anyone out there who knows what the normal vacuum and total advance numbers should be for the 96 pcm?

Also does anyone know the exact function of the 3x wheel on the crank?

Is it possible that the crank position sensor is out of sync with the camshaft position sensor(distributor) causing a limp mode ignition map?

Thanks

 

Mine only advances while running to the mid 20's. And it runs fantastic. Couldn't be better. This confused me too, as everything you read about Fords is they like the timing to be in the 34-38* range with all the advance in. But that's also with a carb, not with a computer constantly monitoring things and fine tuning the advance.

 

The 4.9 cannot SLIP ..it is Gear Driven..like a diesel..there is NO chain......I would buy a new distribiutor http://www.summitracing.com/int/sear...rder=Ascending

 

Yes there is no chain agreed. The harmonic damper however after 17+ years of heat and oil contamination can delaminate and the outer ring can slip.

Replace the distributor? Do you have any reasoning behind this? Bad pickup or something? The link you sent contains mechanical/vacuum advance models which aren't applicable to the pcm controlled timing...

Hmm this is interesting. I put a few miles on mine now and it's running better now than at post #1 as the previous owner had the base timing set by the wrong set of marks. And I checked (the wrong set of marks when reporting the 12 degrees in post#1). It feels a little stronger now, and still no signs of knock. The reported advance numbers (from data stream) haven't changed and still seem low however...

I'll check the fuel mileage this next tank and report back. If anyone has some suggestions in the mean time let me know!

Thanks

 

Well I did not know that ...I have a Diesel now...I had 3 or 4 4.9 's before and I always replaced the Dizzy when I had Timing Issues...Also I beleive the 4.9 is Internally balanced like my 460 so the damper slip does not matter......That is my Reasoning.....Sorry I did not look at all the Dizzy's on that list... Maybe you need a New PCM ?
My 460 is Built with Performance Stuff if you read my Sig ...I like aftermarket stuff Ignition wise....Much better than the Ford stuff.....

 

I have an update. After setting the base timing to factory and driving around for a few days with somewhat improved performance, I thought I might try disconnecting the battery to reset the pcm one last time. This made an obvious change to timing this time. I haven't done any WOT pulls or anything, however currently:

Idle: 16-20* (indicated by scanner)
Cruise: 50km/h (~35mp/h) 25-26* (indicated by scanner)
Light accel: 20*+
1/4 throttle: ~18* @2000rpm

The van feels much more drivable now, it's got torque all of sudden. Throttle position is much lighter now under accell, and response much better. The big difference is the pcm holds onto some timing under load, previously above 1/8 throttle the timing would fall off into some very low numbers. Now my usual around town acceleration stays close to 20* indicated on scanner.

Just to clarify I had reset the pcm by disconnecting the battery several times in the past, but not since timing the engine to factory (using correct marks). This makes me think the 3x wheel on the crankshaft of the 96 is likely used as a checkup feature to test distributor base timing. And it seems clearing SPOUT code with scanner after setting timing is NOT enough if the pcm is in limp mode...

I hope maybe this helps someone in the future. Thanks for all the help.