Hi All,
1988 4Runner. DLX 4x4. I bought her when she was pretty sad. Sitting on her bump stops and all that... I've put a lot of work into her, chasing gremlins, making her look pretty...
Here's what's been done: NEW tps, alternator, wires, plugs, rotor, cap, signal generator, timing chain/guides/tensioner/cover, water pump, oil pump, main seals, fuel pressure regulator, cover gasket, clutch, IAC valve confirmed to be working, IAC hoses are new, etc, etc...
I've cleaned out the plenum, and EGR system, cleaned and rebuilt the injectors.
No matter what I do, she always seems to flutter on her timing. I just did a valve adjustment, and that quieted her down a lot, but that flutter tho...
When I have the timing light on her, she's between 5 and 8. Where 5 is most consistent, and 8 is the high end. I've set her so she doesn't really dip below. There's no pattern to it, like, I can't correlate it to a single piston. She's fine for a few seconds, and then she jumps around, then fine again.
Highway fuel consumption is about 20mpg. Around town, significantly less: about 15ish.

She's not "hard" to start cold, but close. Sometimes it's like 5 seconds of cranking. Sometimes I stop, and try again. Second time is always easier/faster. If I do the thing where i turn they key and then press the clutch, she's starts a little faster.

I'm about to crack the fuel tank and take a look at the pump strainer.

That said, anybody have any ideas why the timing mark might flutter around?

 

An easy one to check for is a worn bearing in the distributor. Remove the cap and push on the rotor. You shouldn't have any perceptible side-side movement.

I will comment that your mileage and starting sound just fine. Particularly for a 20-yr old truck. (Wait, what? Your truck is how old?)

 

Right? Sometimes I forget to cut her a little slack.

Re: the distributor, thanks for the idea. You're talking about pushing it 90 degrees against the direction of the shaft, yes? When I adjusted the valves, I did notice what I thought might be worn gears at the distributor/cam interface. I didn't have time to check play in the rotation. Any idea what "acceptable" play is there?

Cheers for the reply. Thank you.

 

So, no play in the distributor 90 to the shaft. It does rotate 1/4 to 3/8 inch at the tip of the rotor. How much is too much?

 

Okay, I just checked/set the air gap on the signal rotor (signal generator is new btw). It wasn't out of spec, but was on the higher end. I confirmed that there's no play in the signal rotor, and set it to slightly over .2mm, lower end of the range. Manually cranked the engine through a full turn and checked each lobe. Manually confirmed that timing is set to 5.

Took her for a spin and she's a little smoother/quieter. But, with the light, she's still a little fluttery.

So, here's the current working theory: There's a fuel delivery issue, and because there's a touch of excess slop in the distributor drive gear, slight changes in "bang" make the timing flutter a little. She has a new fuel filter, cleaned/rebuilt injectors, and a new fuel pressure regulator. Only thing left is the fuel pump.
There was some black "soot" in the fuel filter when I changed it. So, I'm leaning toward crud in the tank / a clogged strainer. Which could explain why she runs super rough and lean when the tank is low. The pump just sounds too good for me to expect it's failing.

 

Well, I wasn't entirely correct, but I feel vindicated... at least enough that I totally deserve this stiff gin and tonic I'm sipping while I type.

I pulled the fuel pump, and boy, was it a mess. I thought the strainer would be jammed up. There isn't even a strainer. It's just that ribcage skeleton from the OEM one, no filtery cover thing. Also, the short piece of fuel line that connects the pump to the metal line was hard and cracked. There was a new hose clamp, but the old one was still there, dangling loose. Same with clamps on top of the hangar. The pump itself looked fairly new. I'm guessing this was a poorly done replacement. Just the pump, not the hose or strainer.

The electrical connections looked like they had not been cleaned when the new pump was installed. As I was scrubbing them with a wire brush, the loop at the end of the ground wire fell apart in my hand. Great. It doesn't have much slack at all. So, yeah. New piece of fuel hose, clamps, connector. Reinstalled.

It cleaned up the timing flutter slightly. Just because she idles a lot more smoothly. But, it's just the slop in that drive gear. No way around it, I think.

That said, I'm not sure if I fixed a leaky fuel connection, or if I fixed a low volt/amp situation at the pump. I'm leaning toward the leak. This would explain the longer start times after sitting (and the fact that almost no fuel came out when I opened the line the first time). Right now she's starting after like one crank, but we'll see how she does in the morning.

The rough idle is pretty much gone, and she's no longer doing the thing where I have to shift early because she's out of breath.