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2.3L ('83-'97) Bucking under load, no power, poor MPG


cstarbard

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Hey guys,

Hope everyone is well. Having a problem with my 1996 2.3 4x4. Here's what happens:

Drives normally for the most part. Idles good. Under moderate to hard acceleration, or when trying to maintain highway speeds, the engine seems to miss. The truck jerks/bucks pretty bad during this. If you ease up on throttle, problem lessens. I'm also experiencing very poor mpg compared to what I've gotten from this truck historically, and in general, the truck just lacks power that it used to have. No CEL, no pending or trouble codes.

Here's everything I've done or checked.

-No apparent loss of coolant
-Spark plugs are OEM spec, I believe motorcraft. They have like 40k miles on them. Did them last tune up. I haven't pulled them to look at (it's on the to do list) but they are all still tight, I just checked.
-Replaced both coil packs (their plastic covering was breaking down, they were actually sparking through the cracks. Yikes.)
-Replaced the plug wires. It was time anyway.
-Replaced the pcv, it was time.
-Key off, cycled a few times, Fuel pump has good pressure (around 40-45 PSI). It does NOT fall rapidly with key off. Very slow. Like 20 sec to drop 2 psi.
-All injectors have 14.5-14.7 ohm resistance
-All injector harness plugs have 12v with key on
-Air filter not plugged, properly seated, no obvious vaccuum leaks
-Truck stalls if you disconnect IACV while idling. Feeling skeptical that there is a vacuum leak. Did intake gaskets recently, changed a bunch of vacuum hoses that were old and crappy.
-Tested voltage output of TPS while moving throttle plate by hand. It checked out perfectly.
-Did an extensive test of the MAF with multimeter. It tested perfectly.
-Replaced fuel filter
-Confirmed that purge solenoid is not stuck open
-Both 02 sensors were replaced a few years ago. As I recall I tested them this spring and they were fine.

What I plan to try still:

-Removing and inspecting each spark plug
-Unplugging 1 injector at a time while idling and see whether it changes the idle. Wondering if one might be clogged?
-Test vacuum with a gauge. What value should I be looking for?
-What else should I do to look for a vacuum leak?
-Should I test the fuel pressure regulator?
-Is it possible my timing belt skipped? I replaced it 2 years ago.
-I plan on having my wife drive it while I watch live data on the scanner and see if I notice anything weird about fuel trims, especially while its bucking

Any help is appreciated. Feeling a bit lost.
 


Rock Auto 5% Discount Code: 7FA902352B4C01: April 5th, 2021

RonD

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Check FPR's(fuel pressure regulator) Vacuum hose for gasoline, shouldn't be any of course
Replace FPR if gas is found

Fuel pressure should hold for months above 20psi, so check FPR's vacuum hose

Clean MAF sensor

With a 1996 2.3l Lima the engine should run fine on one coil pack, so unplug one coil pack and start the engine, if idle is smooth but lower then all spark plugs are working on that side
Repeat for the other side
If there is a steady misfire from either coil then you have a bad spark plug or wire on that side

Dual spark plugs are used for better power, there is no "alternating" or there would be no benefit


Test for leaking fuel injector, or FPR
engine off
Turn on key
Press gas pedal down to the floor and hold it down all the way, 0 RPMs + wide open throttle = no injector pulse
Try to start engine

It should NOT start, it should no fire at all, injectors are OFF
If it starts then fuel is leaking in from somewhere

This is called Clear Flooded Engine Mode, all fuel injection computers have this
 
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cstarbard

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Thanks for the help as always Ron.

Check FPR's(fuel pressure regulator) Vacuum hose for gasoline, should be any of course
Replace FPR if gas is found

It smelled ever so faintly of gas, but there was no actual gas in it after running. The smell was still incredibly faint

Fuel pressure should hold for months above 20psi, so check FPR's vacuum hose

I took the vacuum hose off the truck, plugged one end with my thumb and blew into other end. Extremely hard to blow into. It seems to be in great shape

Clean MAF sensor

I did this already :(

With a 1996 2.3l Lima the engine should run fine on one coil pack, so unplug one coil pack and start the engine, if idle is smooth but lower then all spark plugs are working on that side
Repeat for the other side
If there is a steady misfire from either coil then you have a bad spark plug or wire on that side

I did this today. I didn't notice a difference in the misfire on either side. It behaved the same way regardless of which coil I unplugged. In both cases it idled ok, could hear and feel what sounds like a misfire as I pressed the gas pedal. Sort of stumbled around 3k rpms, which is where it seems to happen on the road

Disconnecting the coils set a CEL. The freeze frame data showed a very reasonable ECT reading and my short term fuel trims were +21.49 %. Does this mean the computer thinks it's running lean?


Dual spark plugs are used for better power, there is no "alternating" or there would be no benefit


Test for leaking fuel injector, or FPR
engine off
Turn on key
Press gas pedal down to the floor and hold it down all the way, 0 RPMs + wide open throttle = no injector pulse
Try to start engine

It should NOT start, it should no fire at all, injectors are OFF
If it starts then fuel is leaking in from somewhere

This is called Clear Flooded Engine Mode, all fuel injection computers have this

I tried this. Truck did NOT even try to start. So I guess we have ruled out the FPR or leaky injectors?
I also unplugged the 2 fuel injectors I can reach while it was running. The idle fell and stumbled, so those 2 are not clogged? I'll try the other 2 eventually, I will have to remove the throttle body to unplug them each time
 

cstarbard

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Also I tried the vacuum gauge at idle and it was a steady 20
 

cstarbard

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Ok so I have some updates.

I had my wife drive the truck while I watched the live data. I am further mystified because everything looked pretty good to me. Values didn't change noticeably between OK driving and bucking. All values below were noted as truck was bucking, several different times. I forgot to take pictures of the live data but this is what I recall.

02 sensors were both fluctuating between 0 and .5V
Short term fuel trims were in the single digits (~+6-7)
Long term fuel trim was also in the single digits (~7)
Totally reasonable ECT reading based on outside temp
TPS readings made sense. After the drive I parked, engine off, WOT showed 93% for TPS. "Fully closed" is always like 17%
Never any more than 25 degrees of spark advance, spark advance increasing with rpm
MAF readings seemed fine... started around 2.3 or 2.5 and never got much higher than like 6 as I recall

This was like a 20 minute drive around town at various speeds up to maybe 45mph, after idling for 10-20min before the drive

Am I missing something here? It honestly seem to idle great, pretty consistent, like 750-900rpms. Also runs ok, but once a certain amount of load is applied, it just bucks, and the more you try to accelerate or the faster the speed you try to hold, the more powerless and bucky it gets and the mileage is just awful

I will be pulling the plugs this weekend and taking pictures and inspecting them. Again, any suggestions or help is appreciated.
 
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tomw

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Spark breakdown under load will cause bucking. Bad plug wires can cause symptoms of the same thing.
Did you measure the ohms of the plug wires? They can be broken internally but appear intact. Use a VOM and note
the ohms. I think about 20K per foot, but that's off the top of my head. If you get overload 0L, theyz open.
tom
 

cstarbard

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Spark breakdown under load will cause bucking. Bad plug wires can cause symptoms of the same thing.
Did you measure the ohms of the plug wires? They can be broken internally but appear intact. Use a VOM and note
the ohms. I think about 20K per foot, but that's off the top of my head. If you get overload 0L, theyz open.
tom
Hi Tom,

Thanks for the helpful response. I put brand new plug wires on right before making this post since it was about time and there was some damage to the insulation of one old plug wire.

Putting new wires on made minimal if any difference in the symptoms going on.

I plan on replacing all the plugs tomorrow... I really hope that does it
 

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Hey cstarbard, I will be watching your post closely. I have a 94 with the 2.3 lima engine. It is doing the exact same thing you are describing. I bought the truck this way almost a year ago, good news is that is hasn't gotten any worse. Bad news, I have thrown a lot of parts at it and nothing changes the way it runs. New plugs, wires, filters, coil packs, checked for air leaks. My son drives it and is amazed at how predictable when it skips. Good luck. If I come across anything else I will surely let you know as well.
 

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Have you tried defeating the EGR system? If the EGR valve sticks, you could be getting more 'inert' gas into the combustion chamber than the computer thinks is there, and if you do, misfire is more likely.
Have you looked at the airflow and fuel flow values when cruising? Using a scan tool, you should be able to tell whether the readings are 'within norms' or outside. The LT and ST fuel trims will also tell a tale, and if within good norms, should eliminate fuel supply from the problem set. OTOH, a interruption in flow would be of short duration, perhaps coming and going before the trims can even notice it.
tom
 

cstarbard

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BrHotte: wow that sounds exactly like the problem I'm dealing with. Sorry to hear that! I hope I solve this for both of us!!

Tomw: as always thank you for your informative responses. Without you and RonD we would all be doomed. How does one defeat the egr? Disconnect it from the intake manifold and cover the hole on the intake with a block off plate?

Yes, I have looked at air flow and fuel trims while cruising. I dont totally understand what I'm looking for with the maf value (so please feel free to school me) but I see like 3 at idle and increases with acceleration, rpm etc, the highest I saw was like 6.67

As for short term fuel trims, they are high at startup sometimes (in the realm of 10-12) but are almost always under +10 while driving. Sometimes I would see up to +13 ish while driving but very seldom, and it seemed to occur randomly. Sometimes the fuel trims dip negative, to like -1.6 or -2, but that was very infrequent. They consistently hang in the positives, mostly under 10

One long term fuel trim is like +7 and the other long term is 99.2

I changed the plugs today with motorcraft platinum sp-432. Gapped them all to .045. The truck has way more power but the bucking persists, exactly where it did before.

The plug wear us interesting. I'll upload pictures later. The plugs of the two cylinders towards the rear of the engine (3 and 4, presumably?) Had the electrodes basically melted off flush with the ceramic. The first 2 cylinders had electrode wear, but nothing like that. The wear on those seemed reasonable enough.
 

cstarbard

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Ok, here are the old plugs. These had somewhere between 40k and 60k on them. I think it was closer to 40k but I don't remember exactly when I changed them. 2nd pic is intake side, cylinders 1 and 2. 3rd pic is exhaust side, cylinders 1 and 2. 4th pic is intake side, cylinders 3 and 4. 5th pic is close up of wear on intake side, cyl 3 and 4. 6th pic is exhaust side, cylinders 3 and 4. Very last pic is a closeup of exhaust side cyl 4, had some black gunk on the finger when I pulled it out. I don't think it got dirty coming out, the black gunk was like between electrode and finger when I pulled it out so I figure it was like that in the cylinder

What do you guys make of this wear on the cylinder 3 and 4 plugs? I was suspecting leaner condition in those 2 cyls based on the electrode damage- am I interpreting it right? If so, could it be that the injectors on 3 and 4 are a little clogged and would this explain a lean condition in 3 and 4
 

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tomw

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Get some OEM plugs. Motorcraft or Autolite. The center electrode wear is something I have not seen previously. I have seen them with very rounded shape, no corner or edge at all, but never worn like that.
I think I would be looking for a leak that allowed #3 & #4 to run lean. Lean will give hotter temps, and may be the cause for the wear. Nothing against NGK, but but but... try some OEM plugs. Or AC/Delco, I think their electrode material is a bit stronger. I definitely do not recommend Champion as their electrodes did not last in the ones I used.(not in a Ranger)
If you have a vacuum line that is plumbed into the intake... feeding #3 & #4... it could have loose fitting, or a crack that opens up when the engine torque loads the mounts, and forced the engine to tile a slight bit. The corrugated air feed tube has broken on some, and has lead to extra air the MAF didn't know about...
I did not look at the other plugs, just the exhaust in those two images. the #2 plug looks as if it is VERY lean, with zero deposits on the center ceramic. #3 and #4 are a bit lean looking also, though not as much.
I do not have this thread in my head, so ask. Did you check fuel pressure? Did you measure fuel delivery volume? Pressure is not enough, the pump may(will) develop good 'dead head' pressure, but fail to deliver volume enough to run the engine. Notable especially if you do a long hill climb, or cruise at highway speed and then try to accelerate. If fuel delivery is marginal, it will likely become more apparent when it has been running 'at the limit' for a while(cruise @75 / hill climb) and you THEN ask for more...
You can test volume by jumpering the relay or EEC-IV plug, and using a gauge/bypass to capture volume over time. Then do some math...
tom
 

cstarbard

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Get some OEM plugs. Motorcraft or Autolite. The center electrode wear is something I have not seen previously. I have seen them with very rounded shape, no corner or edge at all, but never worn like that.
I think I would be looking for a leak that allowed #3 & #4 to run lean. Lean will give hotter temps, and may be the cause for the wear. Nothing against NGK, but but but... try some OEM plugs. Or AC/Delco, I think their electrode material is a bit stronger. I definitely do not recommend Champion as their electrodes did not last in the ones I used.(not in a Ranger)
If you have a vacuum line that is plumbed into the intake... feeding #3 & #4... it could have loose fitting, or a crack that opens up when the engine torque loads the mounts, and forced the engine to tile a slight bit. The corrugated air feed tube has broken on some, and has lead to extra air the MAF didn't know about...
I did not look at the other plugs, just the exhaust in those two images. the #2 plug looks as if it is VERY lean, with zero deposits on the center ceramic. #3 and #4 are a bit lean looking also, though not as much.
I do not have this thread in my head, so ask. Did you check fuel pressure? Did you measure fuel delivery volume? Pressure is not enough, the pump may(will) develop good 'dead head' pressure, but fail to deliver volume enough to run the engine. Notable especially if you do a long hill climb, or cruise at highway speed and then try to accelerate. If fuel delivery is marginal, it will likely become more apparent when it has been running 'at the limit' for a while(cruise @75 / hill climb) and you THEN ask for more...
You can test volume by jumpering the relay or EEC-IV plug, and using a gauge/bypass to capture volume over time. Then do some math...
tom
Thanks again Tom. Theres a lot to digest there, I'll investigate those leads. Thank you for the extensive analysis of the plugs!

I installed new plugs over the weekend. Motorcraft Sp-432, recommended replacement of original Motorcraft plug. Gapped to 0.044 as instructed.

Truck has more power now, still bucks exactly the same though

As for vacuum leaks, I've looked many different ways and have not found any. Truck will stall if you unplug IACV. Tried propane, that did not find any. I have taken most lines off and tested them by capping one end and blowing in other... So far they are all solid but I have a few left to try
 
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BrHotte

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cstarbard, fwiw, I know we are battling similar issues. I did remove my egr valve today and checked it all out. I seems to be working fine. I reinstalled it and surprise! no change. Just thought dI would let you know.
 

cstarbard

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Thanks BrHotte. I wish it solved it for you.

In other news. I decided to clean the maf again. Last 2 times I just sprayed it liberally with Maf cleaner. This time I decided to remove it for closer inspection and a better cleaning. I could see that there were still deposits/dirt on it. I used qtips and rubbing alcohol to clean it. This removed a lot of dirt from it. I'm now convinced this is the only way to truly clean a Maf.

It did in fact make a difference. The values are lower overall and the truck has a little more pep and the bucking is noticeably better... But its still there unfortunately
 


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