Abnormal Engine... Pulse(?) Under Acceleration

[myotis1134]

Hey guys, sorry about the title - I'm not entirely sure how to accurately describe what I'm observing, so it's been difficult to effectively search for a thread that already deals with this issue.

The car runs great all the time since the whole 'post 120k failure' thread, but I have noticed that under acceleration I get what seems to be "pulses" where the engine surges for just an instant, in a consistent rhythm like 1-2...3 approximately every 6-8 seconds.

These "pulses" feel like I've jabbed the throttle and instantly released it, but way faster than I could do with my foot. I first noticed this in 4th gear, where it is most apparent. After becoming aware of this pulsing, I attempted to isolate the conditions in which they happened and found that I could also observe them in 3rd and 5th gear - they were just not as pronounced. The pulsing does not seem to occur when the vehicle is not in gear, or while idling - only when in gear and under acceleration - hard or light.

My first instinct is that it's related to the fuel system - probably the pump, but I'm also thinking that perhaps the pulse dampener on the fuel rail could perhaps be pooping out?

I'm thinking fuel because the pulses feel like a little extra gas is being pushed into the engine, producing just a little extra HP.

In the interest of full disclosure, I swapped the 48# injectors (which didn't work at all) with 26# ones for the ATX - I was told the ECM could handle/compensate for the slight increase in flow. Because these ARE larger injectors than stock, I suppose they also should be placed on the list of potential culprits.

Thoughts or solutions? Thanks in advance.

 

[luigisho]

Those injectors are on the top of my list. Did you check to see if any codes got tripped? I would look for a used set of oem 3.2 injectors.

 

[rubydist]

I would start with cleaning the mafs and checking the tps. I have seen engines surge when the mafs is dirty and not reading properly and also when the tps has a flat spot on the resistance curve.

The pcm is perfectly capable of adjusting between the mtx and atx injectors, so I am not worried about those being the cause of this issue.

 

[Jbeck]

I experienced a similar effect in my white 90 when I had it and it seemed to happen every time I had a leaking plug well gasket....the oil in the wells would foul giving the spark a new path but not all the time...it seemed to be random and it caused the "pulsing" you have described.... Even after sealing the plug wells and cleaning everything very thoroughly it still would pop up every now and again....I finally replaced the plug wires and it all went away! I talked to a couple friends of mine and they told me that silicone wires will do that with age and submersion in oil....turns out there are detergents and ingredients in engine oil that will actually get "soaked" up into the silicone and stay there causing premature breakdown and spark leakage...basically the plug was not getting ALL the spark.

Idk if this helps or not but good luck!

 

[BRD]

I was experiencing these symptoms along with my secondaries not kicking in properly, and another MAF (an old one I had), cleared up the issues. (I couldn't even get the TPS off to change it)

 

[myotis1134]

OK, so it sounds like I should be looking at the spark side of things.

Swapping out the TPS will be the easiest way to start - I put the old one back on when I was attempting to maintain an idle while running 48# injectors, and the new tps is still in the box.

The plugs and wires are all brand new, and the engine sat for a couple weeks - holding oil, while I did other stuff. I guess that doesn't mean the spark plug well seals have to be good to go, but I put a BIT of sealant on them since that was the original issue that caused me to start the 120k maintenance.

I cleaned the **** out of the MAF while attempting to troubleshoot the 48# injectors, and I completely disassembled the intake manifold, cleaned and greased (where appropriate) everything on the secondary assembly - including the diaphragm valves - simple green is some versatile shit...

@luigisho - I actually did have a check engine light come on for two separate occasions - just for a second before going away - and the codes were for running rich. I can't say what they were because apparently I didn't record them.

I'm going to swap out the tps and see what happens.

 

[myotis1134]

Looks like I was sold a bad tps...

Swapped the old one out, started it up and let it idle for about 3 minutes, then revved it up a few times. The new tps removed the RPM dip I'd been seeing, but I got a check engine light after revving, and pulled these codes:

121 - Throttle Position (TP) sensor out of range – TPS

123 - TP is/was high or short to power – TPS

173 - Oxygen sensor not switching – system is or was rich – Single, Right or Rear HO2S – Fuel control

177 - Oxygen sensor not switching – system was rich Left or Front HO2S – Fuel control

Guess I'll go pick up another tps and see what happens.

 

[rubydist]

Its possible that it is not the tps, but the wiring from the pcm to the tps.

Reset all those codes so you start over to make sure none of this is left over from the injector fiasco.

 

[myotis1134]

Pretty sure the TPS is the source of these issues.

Forgot to pull the new (bad) tps this morning, and ran into town... Everything was kosher until I hit the highway, then it ran like shit:

- Idle began surging up to 3k, then down to 1.5
- At the stoplights idle wanted to stay at 3k
- Check engine light was on most of the drive - haven't pulled the codes yet, but I'm guessing they are all what I pulled before.

Naturally nobody in town is carrying a new tps... Sucks to live in AK sometimes.

 

[rubydist]

For others reading this thread in the future, a similar symptom of the engine having a slight surge or slight stumble will be noticed in some cases as the a/c compressor kicks on or off (more so when cycling on). Some of these a/c compressors seem to take a lot of torque to start turning, so as the compressor cycles on, some of the cars will have a noticeable hesitation or stumble for an instant.

 

[FastCAD]

Looks like I was sold a bad tps...

Swapped the old one out, started it up and let it idle for about 3 minutes, then revved it up a few times. The new tps removed the RPM dip I'd been seeing, but I got a check engine light after revving, and pulled these codes:

121 - Throttle Position (TP) sensor out of range – TPS

123 - TP is/was high or short to power – TPS

173 - Oxygen sensor not switching – system is or was rich – Single, Right or Rear HO2S – Fuel control

177 - Oxygen sensor not switching – system was rich Left or Front HO2S – Fuel control

Guess I'll go pick up another tps and see what happens.

(I)dle -(A)ir -(C)ontrol. Note: the IAC does not throw a code.
The (old) "shotimes" forum covered this and many other helpful issues.
Is there a "shotimes: archive out there?

 

[BaySHO Performance]

Not sure you are referring to this, but:

http://web.archive.org/web/20120719002225/http://www.shotimes.com/php-bin/

Nowadays a lot of that info has been superseded by:

http://wiki.wikisho.com/wiki/Main_Page

 

[Greg Corcoran]

Don't mean to hijack the thread, but I have a related question.
I have a '95 MTX with similar pulsing, only when engine cold, and worse in winter with weather cold. At 3000 - 3500 rpm the engine surges or pulses. When engine and weather really cold couldn't get to 4000 rpm. Originally violent bucking when freezing or near freezing. Cleaning MAF no change. Replaced MAF with a larger Ford MAF, no longer violent bucking, but still disturbingly pronounced bucking/pulsing although could then get to 4000 rpm and secondaries would open and cleared up but felt like going into a 40-50 mph headwind. I'd say it feels like it's rapid bogging and then clearing. O2 sensors were original and were "slow switching" based on codes. I replaced, but no change. No other codes except 542. So I'm further thinking open loop issue before engine warms up some and goes closed loop... Being open loop limits the potential suspects
Now that it's summer it's just barely perceptible and mildly annoying, but this thread got me thinking again about TPS, so I went NAPA to get a new one. They show 5 possible replacements!! for '95 SHO w/ 3.0L DOHC and need to know OEM number of original to pick the correct replacement. I have no clue if mine is the original or not. There is a Ford number on TPS, E9TF-9B989 top line BA and 4Lo8A on second line. I do know I have the standard X2J PCM, and D code CCRM if that helps. Doesn't E9T mean this is off a '89 truck?

 

[BaySHO Performance]

TPS Sensor CX-1426 F2DZ-9B989-BAas opposed to the factory number on the part. There's also this that I've used:

https://www.autozone.com/engine-man...s+215&fromString=search&isIgnoreVehicle=false

 

[zoomlater]

I've been buying the recall kit part number in the link below, comes with two new mounting screws. Ebay has them listed for pretty reasonable prices

https://shoforum.com/index.php?threads/tps-and-napa.111613/#post-1207043

 

[FastCAD]

I've been buying the recall kit part number in the link below, comes with two new mounting screws. Ebay has them listed for pretty reasonable prices

https://shoforum.com/index.php?threads/tps-and-napa.111613/#post-1207043

MOTORCRAFT DY974 {#F2DZ9B989BA} RockAuto.com

 

[Greg Corcoran]

Thanks BaySHO and FastCAD! the F2DZ-9B989-BA Eichlin/NAPA equivalent is on the shelf in Denver distribution center. Will be at my local NAPA in the morning. I presume I disconnect the battery for 5 minutes or so when I change it out to let the computer relearn the new sensor?
Not to jinx it, but what else in open loop could cause rich bogging and pulsing? Last year I changed the ECT to get the cooling fan working, turns out it was offset cold by about 40 -50 degrees. I had been chasing the CCRM and it's wiring to no avail. Paid a professional (former Ford ) mechanic to troubleshoot and viola with new ECT sensor fan worked. The new ECT also had an improvement, but not cure, to the pulsing.

 

[FastCAD]

Thanks BaySHO and FastCAD! the F2DZ-9B989-BA Eichlin/NAPA equivalent is on the shelf in Denver distribution center. Will be at my local NAPA in the morning. I presume I disconnect the battery for 5 minutes or so when I change it out to let the computer relearn the new sensor?
Not to jinx it, but what else in open loop could cause rich bogging and pulsing? Last year I changed the ECT to get the cooling fan working, turns out it was offset cold by about 40 -50 degrees. I had been chasing the CCRM and it's wiring to no avail. Paid a professional (former Ford ) mechanic to troubleshoot and viola with new ECT sensor fan worked. The new ECT also had an improvement, but not cure, to the pulsing.[/QUOE

Thanks BaySHO and FastCAD! the F2DZ-9B989-BA Eichlin/NAPA equivalent is on the shelf in Denver distribution center. Will be at my local NAPA in the morning. I presume I disconnect the battery for 5 minutes or so when I change it out to let the computer relearn the new sensor?
Not to jinx it, but what else in open loop could cause rich bogging and pulsing? Last year I changed the ECT to get the cooling fan working, turns out it was offset cold by about 40 -50 degrees. I had been chasing the CCRM and it's wiring to no avail. Paid a professional (former Ford ) mechanic to troubleshoot and viola with new ECT sensor fan worked. The new ECT also had an improvement, but not cure, to the pulsing.

Erase your old codes to avoid false readings. Usually disconnecting the battery for at least 10 minutes with the headlights on and pump the brakes a few times will run down the PCM backup power supply. After installing the new TPS a drive of about 10 miles will allow the TPS to relearn.
The IAC also plays a part with surging problems this part behind the throttle body does not throw a code. This unit might give you a clue that there is a problem when the tach is not steady at 1000 rpm (warm, a/c off) Some have had success with taking the back end off and cleaning the unit. Replacing this unit is a real p.i.t.a. You can let the SHO sit warm at idle disconnect the wire connector the SHO should idle down steady at 800 rpm wait a couple of minutes and let the PCM relearn the base idle and then reconnect. The SHO should return to 1000 rpm. Replacing this part should not be a place to cheap out. The "Delphi" unit is an OEM replacement. This part is "vehicle-model" specific and is "not" interchangeable. About $54.

 

[rubydist]

Greg, when I read your description, I thought it more likely to be a sticky iac. I have had a bunch of issues with those over the years, including one bad (sticking) right out of the box new. If the tps doesn't fix your issue, its most likely the iac.

 

[myotis1134]

Napa sold me a bad TPS. I’ve ordered a motorcraft brand TPS from oreilly’s - should be here on Monday - I’ll post about how it affects things.

I’m done screwing around, and ordered a brand that is far less likely to be faulty- after seeing how much a bad/old TPS can (potentially) affect the engine performance.