Ok, got feelers about this one out and about. Looking for Ideas, as this one is annoying the snot out of me.

Details for the last two years worth of fun to prep this:

89 BII 2.9 RWD.
Replaced both heads with new ones
Full tune up, inc fuel filter
New O2 sensor
New TFI
New IAC
New TPS
Rebuilt injectors.
--recent-- Alternator (tested great after install from the local boneyard)

This was done (and a lot more...don't get me started on A4LD transmissions) just to get the ol' girl on the road. It's been getting 20 mpg, so I've been pretty happy, and with the exception of a minor coolant leak fixed last month? (water outlet had a hairline crack--it was never allowed to run low on coolant, and always stayed on the "N" on the guage)

Ok, last week driving to work---It did a quick "Buck". The engine acted like it cut out and in out. Kinda like a power loss--and then it kicked back in normally after a few seconds. At first I figured bad load of gas, but I filled up (16 gal) with a fresh tank..and it's gotten worse. Kinda concerned I'll be stuck high and dry on the interstate. Seems to like doing this mostly while at 55-70---light load to moderate load like going up a gentle incline. Not a lot of big hills to really see what effect a larger load would do.

I hit the panic button LOL..and figured it was a transmission issue again (we are on our 3rd...this one so far has made it a year WOOHOO) Then got past my stupid moment and figured out...Hey, power loss, slight loss in speed...but the engine did not increase in RPM's such as it would if it slipped or downshifted or started gear hunting...The engine RPM just dropped off slightly, and then it self corrected!! Resulting in a bit of a "Bucking" motion...Not enough to trigger a CEL? Didn't even effect the tach any...just dropped off and picked back up with a bit of a "kick".

Now I'm fairly sure the alternator I installed didn't cause this--it was fully tested and was running like a champ when the parts store did an in-car full test. Plus that was done almost a month ago---this is the last two weeks.

The weather hasn't helped...been quite warm, and Wednesday (last time I drove it) It was in the low 90's....(main reason I've not worked on it yet LOL)

At this point I'm looking for ideas...Any ideas on what is causing this issue, because I'd like to nip this before it drops off----as in dies on the highway.

I'll be pulling codes on Sunday, testing the FPR and the TPS just to ensure correct fuel line pressure and the TPS didn't get another bad spot in it. (it's about 1 1/2 year old...while it should be ok? It's easy to test)

A large number of electronic parts did get replaced---heck, this was a learning 'truck' for a boces center...everything was removed and replaced about a dozen times before I replaced everything with good parts LOL. But this issue has me off balance.

Fuel pressure loss? Would create a power drop, and when the pressure returns to normal? Yeah it would jump back into action......

Ignition spark loss? Also would create a power drop, and when it returns to normal? Same thing--It would 'jump' back into action.

The only other annoying thing this truck has done sense day 1? When running...at temp...stop engine and restart within a few moments? (such as a drive through or quick trip to the store) It will restart with a flash of the key. Leave it for a few hours? Very hard to start, turns over fast enough--when it does start? Smells like Exxon....Very gassy for a few moments. Is it related? Probably not, like the mild surge at idle? (new IAC as well, works like a champ...still has a mild surge) Just one of those things I'm living with.

I'm open to suggestions, as this is my daily driver. (driving the wife's tibby until I'm sure I won't get left stranded)

S-

 

Check the wires to the coil for good conection and continuity. They are weak wires to start with and when the butt connections on the coil get pulled a few times they get really weak.

 

I would guess it is the beginning of the end of the TFI module. I have had a thought from time to time to go with the firewall mounted aluminum cooling thing like on the F-series. I just keep an extra in my glove box.

 

Well, if that's the case? Then nothing is made to last LOL! The TFI is under 2 years old, and correctly installed using heat sink grease.

Out of sheer insanity--I'll ask this one. Given the fact this truck had massive amounts of rust and crud built up that made it to the injectors. (two replaced, 4 pulled apart--cleaned, and new micro-filters installed) I even hosed the holy snot out of the fuel rail when I had the injectors out. Talk about CRUDDDDDDDDDDDDD!!..I did flush the lines out and put on a new filter when done--but that nasty stuff didn't just appear out of thin air.

Would there be any advantages to perhaps (yeah...this would be an insane idea) pulling the sending unit, and replacing the fuel sock...and putting on a new fuel filter? Just have this idea there is a lot of crud in the tank that could be be clogging up the fuel sock. I do fill up once a week using about 15-16 gallons every 310 miles or so.

Then again, as insane as that idea might be? I'll do the fuel pressure test first LOL!!

Sidebar notation: Another thread mentioned the ignition switch itself could cause issues-- Now a few days ago I tried to use the "AUX" on the key switch. It turned a bit 'hard' and it didn't kick the radio 'on'. The only odd thing? If the switch was bad, and kicking the system on/off-- That should also make the gauges 'twitch' as well?

I know I'm reaching...and I'll pickup soon (next paycheck most likely) a spare TFI module and keep a set of basic hand tools in the truck. (along with that mini hand tool for the module).

Currently I'm planning on testing the FPR, pulling codes, if any.. Wiggle test, TPS check with a meter (I've been a tech for an arcade company for the last 17 years after being an auto tech for 4...so I know my way around a meter)..

The engine itself appears to be in fair shape from a vacuum standpoint. First startup? 15" of vacuum (open loop).. 18-19" of vacuum (closed loop), and on rapid decel? Pops up to 24" of vacuum. Which if memory serves? Shows that the system is advancing and retarding the timing correctly, and the engine "sealing" should be decent with the 24" popup.

Just some misc brain droppings as I'm winding down from work today. The real suck part? I just took our 75' F250 off the road two weeks ago and pulled the truck bed so we could de-rust and paint the frame--and build a new box for it. Told the folks where it's stored "Murphy's law---I'll pull our backup truck off the road, and my BII will start acting up".... Sure enoughhhhhhhhhh.

(Folks suggested dumping in a mess of fuel system cleaner, aka STP and Duralube---in case it's just a batch of really bad fuel)

S-

 

I suspect any old ignition switch (electrical portion) and don't hesitate to swap them out, after which I gut the old one to inspect it.

 

> The TFI is under 2 years old

I have had them die just because of the extended use and high heat, even fairly new.

> Another thread mentioned the ignition switch itself could cause issues

Yes, though the symptom many times is the gauge will peg all the way or not move at all. You would check the wire on the starter solenoid.

One thing you might want to check is the low pressure valve before the high pressure fuel pump. It looks like a fuel filter, right next to the fuel tank, and that is all I thought it was. Until it was pointed out here on this board that it retains fuel pressure in low idle and going up the hill situations.

The bucking, losing power, and cutting out is the usual sign of the TFI dying.

 

Well, this may or may not be the cause of the bucking. However it does explain the gassy smell after it's started...after sitting for about 20min to an hour.

Put the gauge on the valve to check the pump and FPR. Have 32lbs with full vacuum, and 40 with no vacuum. However I left the vacuum hose unhooked for a short while--and after about 5 minutes? Steady drips of fuel out the vacuum hose. This would make sense of the gassy hard to start problem...it's pre-loading the intake with raw fuel after sitting for a short while.

So the FPR is toasted, and I suspect this could also create the issue with the power problems. Sure it's running pressures up and down with vacuum, however I left the vacuum gauge on the hose at about 20inches of vacuum--zero fuel loss, and the pressure sitting 'off' didn't drop for several minutes.

Now would a break in the rubber seal possibly do this?: At lower power and high vacuum--it's in a position where it wouldn't leak by. However at lower vacuum (I have a driving vacuum gauge on my dash) Once the 'load' hits about 5" of vacuum during cruse speed going up a slight incline...that puts the rubber seal just at the right spot where it starts to seep fuel into the intake. Now that would create a 'rich' condition, and the computer would attempt to lean out the mixture....then once corrected? The cycle repeats again.

This is going to get replaced in any event---and I'm also planning on saying "Screw it" and pulling the entire disty out and replacing it with a rebuilt one complete with new TFI and pickup coil already replaced. (I'll scarf off the TFI from the old one before returning it for the core. Should make a good spare) I've been bitten before by the pickup coil in the disty failing with busted wiring in the past, and it's the factory one. (over 20 years in service).

Any ideas or feedback?

Also as a side bar note-- I did find at napa a replacement FPR that has a low cost of about $25 bucks. If the warranty is good, I'll probably give it a shot. That way I can cover the expense of the upper intake gasket and rebuilt disty at the same time.

S-

 

I have personally had an ignition switch act like your problem it actually came apart, it's been awhile but I believe it's riveted together, I think I ziptyed it together for a temporary fix. I could wiggle the key kinda hard and make the bronco cutout. Steve