2002tii intermittent loss of throttle

[kmoy2002]

I recently took the tii out for a 20 mile trip and the car starts, runs (seemingly) fine, and even hit a mixture of freeway/street driving. The issue that I noticed this time is that randomly, I'll get a complete loss of throttle. Engine completely unresponsive to throttle engagement. 

 

I had this issue so I coasted off the freeway onto the service lane and the engine suddenly kicks back and I got throttle response again. I resumed driving to my destination with no additional hiccups.

 

On my return trip hours later, I took a right turn to get onto the freeway and the same issue occurred again. Complete loss of throttle unresponsive to pedal engagement. I thought it was a fuel pump issue but the engine never died. It hovered at 1k just nonresponsive to throttle. A few moments later, I got throttle again and was able to get back onto the onramp and continue my trip back home; again without any further hiccups.

 

I'm a little at a loss for what this might be. I thought it was the fuel pump however the engine never died and I've already had the fuel pump replaced with the Bosch e28 fuel pump. I've also changed out the fuel filter up near the radiator. I've already had a new set of plugs, wires, and distributor cap installed with less than 4000 miles on the set however granted that was back in 2016 when I got the car back on the road.

 

I've been reading this might be a coil issue? Could this be a ignition issue? Should I replace coil, points, condenser, cap? When I did the plugs and wires back in '16 I used NKG BP6ES and it's ran fine to this date.

 

Let me know what everyone thinks.

[Son of Marty]

Check the filter screen on the fuel level sender in the tank, there's also a screen at the fuel pump but if you replaced the pump it should be good.

[danco_]

Start by checking ground straps and grounding points in the engine bay. This is pretty simple to do. 

 

-negative battery terminal and corresponding wires

-ground strap from block to battery neg terminal

These are the two I would start with.

 

I've heard of intermittently failing coils, so don't rule that out. 

 

 

If all else fails, throw the car away, it is broken. 

 

/sarcasm

[Glen Karr]

I had a similar issue.  Turned out to be water in the fuel.  I had tanked up at a country store out in the boonies after a long drive with the BMWCCA group.  Evidently there was water in their tank. Didn't clear up until I drained the fuel tank.

Glen

[bergie33]

32 minutes ago, Son of Marty said:

there's also a screen at the fuel pump but if you replaced the pump it should be good.

Probably no screen at the pump since it was replaced with the E28 pump.  That being said, it makes it more likely that crud made its way up to the filter in the engine compartment. I know you said you replaced the fuel filter, but didn't say how long ago.  If it wasn't too recent, might be a good idea to replace it again.

[jgerock]

If the engine still runs but there isn’t a response to the pedal, I’d physically inspect the throttle pedal arm under the car. Bet the splined arm is either loose or stripped.

[Swiss 2002Tii]

I would go with Jim on physical limitation/slip. Slippage at the lever makes sense, as this would mean no mechanical input to the pump.

Also, the central pivot for the long and short throttle linkages can get hung on the water hose from the WUR to the block.  I had to tie my hose down with a zip tie that that it doesn't impede the central linkages.

 

When the problem occurs, you can manipulate the throttle linkage at the vertical rod coming up from the gas pedal.  You should be able to see which point is slipping if that is indeed the problem.

 

[SydneyTii]

I agree with the mechanical issue, the small nut and bolt maybe loose and the “pinch” fitting able to move on the shaft, hopefully it’s not worn!

If not that then crude in the big metal filter, replace it see if it helps, check all your screens as well especially the little one at the pump union bolt, can’t see ignition in this, but I’m famously wrong which causes me nice looong fault finding time!??

[Solarphil]

I’d third the splined shaft under the car at the pedal box lever. It’s a problematic joint on the best days, not designed for decades of use. 

[lilmo]

Are you running Pertronix in lieu of points?

[kmoy2002]

Thank you everyone for the replies. I finally had a chance to look over all these items this afternoon.

 

All the physical linkages pivot and articulate as they should without any signs of slipping. I manipulated the linkages by hand and by throttle and they all seem to be tied together.

 

I pulled the battery and looked at all the ground straps and those too are all tight and tied to where they're supposed to.

 

The car is still running points. In addition to what I mentioned in the initial post, I had new rotor, points, cap, wires, and plugs. The only item that I haven't addressed with the electrical are the coil and resistor. 

 

Fuel wise, I've changed the fuel filter 2 times since reviving the car in 2016. During that time, I had entirely new fuel lines run from tank to front along with the e28 fuel pump.

 

It's a very peculiar symptom and doesn't happen all the time. Any other leads?

[Son of Marty]

Have you checked the fuel pick up screen at the foot of the fuel level sender?

 

 

[kmoy2002]

Thanks @Son of Marty just pulled this morning and the pickup screen looks good. I had forgotten they replaced the pickup when they ran new lines.

 

 

I also bench tested the coil. 7.26 K ohms + to center and 3.4 ohms + to -.

 

Not picture is the resistor and that read 1.8 ohms.

I

[Swiss 2002Tii]

One problem that drove me crazy and was very hard to diagnose....

 

I added a RF-controlled relay to my fuel pump circuit years ago, and in that process I used an 18 gauge wire.  That caused the pump to be starved of current when it warmed up.  The motor loses some efficiency as the winding heated up.  It failed like clockwork about 30 minutes into every drive.  I removed the relay circuit and pulled new 12-gauge wire all the way from the battery to the pump and problem was solved.  Self-inflicted; drove me crazy for six months, and resulted in an epic thread here on the forum with terrific support along the journey.!

 

I'm not suggesting you did a wire change, but there might be something about your fuel pump or circuit that should be checked.  Investing a few $$s in an in-line fuel pressure gauge might be worth the time and expense to see what the pressure is while in failure mode.

[golftii]

Couldn't exactly tell from your response Saturday but did you physically confirm the gas pedal is tightly fixed to its shaft under the car? i.e. the splined shaft under pedal box mentioned by others above? I had similar issue recently, and similar symptoms that idles fine but throttle weak/inconsistent. It was simply loose and needed a good tightening.