98 SOHC - Hesitation driving me crazy! Help needed...

[2000StreetRod]

Other STFTs & VIS

There are multiple STFTs to display. With my generic scanner some of them were not applicable. Did you try reading all of the possible STFTs?

I think the knock sensor connector is next to the passenger side valve cover PCV inlet port shown in the photo below.

According to my wiring diagram the wires are yellow/red and dark green/purple which seems to match what's in the photo.

The VIS vacuum actuator could be moving to the limits but slowly due to friction from carbon build up in the runners. I've seen the runners on the Mustang V8s but not on the V6. I believe there were two vacuum motors on the V8s (one for each bank). Can you disengage the control rod from the vacuum motor and move it with your hand to check the friction? Or there could be a leak in the vacuum motor diaphragm slowing its movement. Do you have a hand vacuum pump to test it for leaks? I would perform those checks before being completely satisfied that the VIS is working properly. With everything connected and the engine running in Park you should be able to watch the actuator move as the engine speed increases from 2500 to 3000 rpm. However, it will be hard to determine if the slow movement is causing the hesitation or if the hesitation is causing the slow movement.

 

[my98nnj]

A quick note on the VIS. I just had to remove the top cover on my 98 to access a few items and discovered my VIS rod had slipped off.

I thought this was odd, being my truck ran perfect. I noticed no hesitation in it at all.

I don't think the VIS system would cause any hesitation, mine didn't.
I don't even feel any difference now that it's connected and working properly.

My .02 Hope it helps.

 

[2000StreetRod]

Actual vs theoretical

Thanks so much for that information my98nnj! Since I don't have the VIS on my 2000 I was going strictly by possibilities whereas you have first hand knowledge. That's what's so helpful about this forum. Now the VIS can be eliminated as the source of the hesitation.

The lack of driver noticeable performance difference and reliability issues is probably why Ford dropped it.

 

[gilly]

2000StreetRod, Thanks for the pic and all of your help and suggestions so far, I really appreciate it! - I'll have another look for the knock sensor loom when I get more daylight. my98nnj is right about the VIS. I do notice a lack of power at top end with it disconnected though, and the valve will hold vacuum if I take the line off and cover the end with my thumb, it'll hold open nicely.

My scanner definitely will not display STFT's at all, or o2 readings, very annoying!

Here's my current thoughts:
1) Bosch Platinums aren't helping things. I can't buy (reasonably priced motorcraft plugs but I'm looking at sourcing some from the US. Even these bosch platinums set me back around $25US each!) I've hardly read a positive comment about these on the forums, I think it's worth changing out and I've heard they are only like $5 each over there? Worth trying if that's the case.

2) Knock sensor is over active/faulty - I've spoken to a few people who have tracked a similar issue down to something like this.

3) Carbon buildup causing excessive pinging, leading to retarded timing, and therefore a hesitation

4) Insufficient voltage to coilpack/fuel pump to supply demand - this is a long shot but hey it's possible in both cases.

 

[storlied]

Get rid of those Bosch plugs, no one has any luck with them, even on other Forums. Use Autolite Double Platinums.

 

[jah81592]

My thoughts

Variable intake runners- unplug the vacuum from the vacuum motor and plug the vacuum line (temporarily) and tie valve in the open position (the natural state is closed). This can be done in a matter of minutes. No major surgury. Won't hurt a thing!-I doubt this is your problem, but it is worth a try.

Plugs- I always run Champion 401's in these engines. They are a standard copper plug and will easily last till your next tune up. So don't get trapped purchasing expensive Iridiums. Recommended stock gap, no more.

PCV- my guess would not give hesitation issues.

Knock sensor- Could possibly pull enough timing but the maximum timing pulled would just cause the vehicle to feel soft it should not cause a hesitation. If the sensor is bad you should get a code after 3 key cycles.

Fuel pressure- 45, 60 doesn't really matter as long as there is not a major fluctuation and is holding steady. Even at 20 psi you wouldn't notice a major driveability issue.

When you mention stalling does the vehicle nose over? Loss of engine power? Or does just feel like the torque converter is locking and unlocking? Does it do this at the same place (same on/off ramp-inclines) or is it random locations? Can you reproduce it easily or is it random? Is it throttle position related? A datalog would definately be nice.

 

[gilly]

Thanks James. I'll have a shot at the VIS soon.

I'd love to check the fuel pressure too one of these days.

My choices of plugs here were Bosch or NGK, so I've now installed NGK Iridiums (I know they're expensive but they've got a much better name than Bosch on these engines!) Unfortunately, there's once again been no difference. Plugs were definitely gapped correctly too. NOT a fun job installing them!

SCT X3 ordered from Henson Performance - looking forward to receiving this one! Once it's here I'll certainly run and upload datalog for those who are interested to see. I know a tune isn't going to fix this problem, but at least the datalogger will show O2's and STFT's etc so that'll certainly be a big help.

 

[2000StreetRod]

Happy New Year!

Congratulations on your SCT X3 purchase! I'm confident you'll be very pleased with the product and service. The X3 instrumentation will allow you to learn a lot about how the PCM operates. Soon your hesitation problem will be identified and resolved! A great way to start the new year.

 

[gilly]

Thanks yeah the X3 won't fix the problem but it sure will help identify it I hope. Plus I figure it'll be a different truck with a decent tune. We've got good fuel here in austraila - regular unleaded is rated at 95 and I run the x on 98 octane constantly so I may as well tune it to suit.

James - the hesitation can easily be reproduced by going to WOT from a standstill or giving plenty of throttle under load conditions. When in closed loop it runs like a dream, once it switches to open loop it seems to lose power momentarily, then take off. If going uphill it will sometimes even fluctuate up and down in revs a few hundred rpm fora few seconds before progressing. Once above say 3200 if runs perfect and will pull steadily with plenty of power all the way through. It doesn't feel like the convertor locking and unlocking to me? Will the X3 monitor any of the transmissions behaviour?

Any more ideas?

 

[gilly]

Well I've done the closest equivalent to SeaFoam that I could find - Subaru Upper Cylinder Cleaner. Certainly runs and idles smoother, still hesitates though!

 

[gilly]

Here's a vid of the problem just taken going uphill from a rolling start at WOT - hope this helps explain things a bit better.

 

[my98nnj]

Thats a pretty good hesitation.

Have you checked for a clogged cat?

 

[gilly]

Thing is it's got plenty of top end performance - I would have thought it would suffer badly with a clogged cat?

 

[gilly]

Well my X3 has arrived from Henson Performance!

I've started DataLogging and I'm blown away by the amount of info you can log with this thing! Fantastic. However I am getting a bit of interference in the logs - spikes reading 10,000 rpm for a fraction of a second, Spark Advance in the millions, etc. Can't work out why this is - I've got the latest version of LiveLink etc and all should be fine with the laptop.

Anyway I can still see what is happening to a degree - if anyone has LiveLink and is interested in viewing the DataLog to help out - the link is below.



CLICK HERE Here's an example of what I'm getting - If you turn on RPM and Spark on the graph and at look at about 152sec and 171sec points, you'll see the points of hesitation and these interference spikes I'm getting from most PID's.

cheers
Gilly

 

[2000StreetRod]

spark advance

I see what you mean about the spikes in your data. Sometimes I get a few but nothing like the magnitude of yours. It may be due to the amount of data you're recording. I would not record the LTFTs, or O2 data until you identify your major problem.

You have a definite problem with your spark advance plot. It does not match the data displayed in the table on the left. But it is obvious from the table data that your spark advance is not working properly. It is dropping to 2 degrees at WOT and 2800 rpm. That's at least 15 degrees too retarded. Also, at light throttle your spark advance is only about 15 degrees whereas mine is around 40 degrees.

I suggest that you add recording your knock sensor retard to see if it is drastically impacting your spark advance. I also suggest that you record your vehicle speed so you can tell if the vehicle is accelerating, decelerating or maintaining speed. The PCM relies on the MAF sensor data to determine the load on the engine so I suggest that you also record the MAF airflow.

With the exception of the spikes your LTFTs look OK.

 

[2000StreetRod]

PIDs

Your STFTs look pretty close to each other. Here's a list of the PIDs that I have found to be useful for analysis: AirFlow #/min, coolant temperature, intake air temperature, knock sensor retard, load, RPM, spark advance, STFT bank 1, STFT bank 2, TP absolute, and vehicle speed. A wideband Air/Fuel ratio meter is very helpful in identifying mixture abnormalities.

I'm starting to suspect what stangman82 suggested at the very beginning of this thread. That your timing was not done correctly when your timing chains were replaced. At the time you said that the timing had been checked and it was fine. How did you verify the timing was correct? Unless you're getting major knock sensor retard I doubt that your timing is correct. You've already replaced your knock sensor so that shouldn't be a problem. The PCM cannot compensate for incorrect TDC/camshaft timing.

 

[2000StreetRod]

plot problem

I suspect the reason that your plot shows little spark advance change is because the LiveLink software scales the vertical axis to accommodate the range of the values logged. Since your spark advance ranges from 0 to 1,000,000 changes between 0 and 40 are insignificant on the plot. A similar thing happened with your O2 voltage exceeding 16.

 

[Doubt Incarnate]

would it hurt to take the manifolds off and check the actual plastic isnt cracked? if its temp related maybe something opens up that isnt supposed to when it gets warm.

 

[gilly]

Thanks for the replies.

We checked the timing by using a timing light - checked out fine. Thing is - I can get it to pull fine all the way to 5500, this hesitation only becomes noticeable under heavy acceleration/load. I would have thought that it would be noticeable under all conditions if the timing was physically set wrong. Also this problem started well before the timing chain was replaced.

I'll record another data log based on your PID's above and upload again for you to look at. The knock sensor isn't retarding much if anything - most I've recorded is 1 degree. I'm looking for the PID that will indicate the switch from closed loop to open loop, as this seems to be right at the instant where it hesitates. Do you know which PID that would show on?

I've tried setting less PID's today and I'm still getting similar spikes - It does worry me that there are so many!?

Intake manifolds were removed, inspected, and gaskets replaced when the timing chain was done - that rules that one out!

I haven't had a good chance to study these datalogs, hopefully soon I'll get to the bottom of all this.

Thanks again for your help and suggestions.

cheers
gilly

 

[2000StreetRod]

open to closed transition

I also have a minor problem when the PCM makes the transition from closed to open for WOT. My A/F ratio is lean when in closed loop and opening the throttle. The PCM is supposed to recognize the rapid throttle opening from the TPS value change and widen the pulse width just like the carburetor pump did in the old days. James has my tune drop to 12.6:1 A/F ratio when I reach WOT but because the mixture is lean going in the PCM takes about a tenth of a second to recover.

I don't know the name of the PID to monitor for open vs closed loop. I believe that a constant STFT indicates open loop.

If you PM me your email address I'll send you my latest datalog of a 2nd gear pull at WOT for comparison. My acceleration times are long because I test on a fairly steep uphill grade at higher altitude to increase my instrumentation time. There will also be differences because of my large MAF sensor and throttle body.

My timing at 5900 rpm and WOT is 21 degrees advanced. My timing at 1800 rpm and constant speed (50 mph) in cruise is about 24 degrees advanced. When your throttle position exceeds 400 your timing plummets. This may because of low power and high load. Your STFT is constant and looks normal during the acceleration. But that doesn't mean that your fuel mixture is correct. However, your O2 voltages don't seem abnormal.

The problem still has me puzzled.