Doggy low rpm, but plenty of juice over 2k rpm (1 Viewer)

[DIRTBIKEUSA]

Has a compression test been done?
Fuel pressure test under load?

 

[gaspain]

take it out of overdrive

 

[CharlieS]

First of all, thank you all for the ideas and suggestions.

I'm not in overdrive, and the compression is good.

I agree that tires can have a significant impact, but in this case, since I can completely dial it out with timing adjustments, I am confident that I'm chasing an ignition timing issue.

More as I fine tune.

 

[lugueto]

Have you checked your fuel pump?

I have seen fuel pumps fail on 80s that cause very low power and stumble at low rpms, sometimes under 3k. I have also seen fuel pumps fail that cause a failure at high rpm. It may be on its way out and causing your bogging under 2k.

 

[DIRTBIKEUSA]

I’m starting g to think this is a fuel delivery problem.

What does you STFT look like?

Is the fuel psi in spec at those suspected RPM range?

Unless you can gear is worn or your distributor shaft bushing is trashed, I don’t see how this is a purely and electrical ignition issue.

Have you tried replacing your crank shaft sensor? Is the CKP tone ring damaged or clocked wrong?

 

[CharlieS]

I replaced the fuel pump and sock yesterday: no change.

Old Fuel Pressure Regulator swapped in: no change.

No current OBD1 codes.

I have not touched the crank position sensor or tone ring (I don't even know where it is).

It is an OBD1 vehicle, so I do not know how to observe STFT. I've monitored it with obd 2 vehicles, and those with factory software tools (vag com, techstream, etc). I don't have a tool
to measure this (that I am aware of).

I have tried what seems like a dozen times to adjust to baseline spec with cyl 1 at tdc, notch on pulley at the 0 degree mark, notch on distributor post pointing at marked tooth prior to installing the distributor, and then timed to 3 deg btdc with DLC jumper in, in neutral, warmed up. It is always horrible off the line, barely moving, even stalling.

If I turn the distributor to what is beyond the range of markings - to what looks roughly like 20 or more degrees, it runs great.

I got a fancier timing light yesterday, where I can digitally adjust the amount of advance.

When acceleration is amazing and no hesitation, I am at 24 degrees (from the 0 tdc mark on the block) when it runs very well (on the road, accelerating strongly).

Anything from 3-15 degrees the thing barely drives out of my yard.

It seems to me that the engine wouldn't run if I was really at 24 degrees btdc, so I imagine this is the offset of one tooth (18 degrees) off plus 6 degrees adding up to the 24.

Question on timing 1fz

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I'll be damned if I can find that one tooth adjustment though. I am about to give up trying.

 

[CharlieS]

If it's on/off power wise I'd double check that the throttle position sensor is dialed in per the FSM.

Do you notice a difference if the PWR button for the transmission is on? Mine is always on (but the bulb is burned out) and one time it was off and I thought something was wrong.

Sorry, I missed this one. The power button is usually on, but this is a much more dramatic loss of get up an go than that button causes.

Funny story: I replaced all of my bulbs in the gear position indicator two days ago and was psyched to have the PWR light back. Then it stopped working yesterday. Either that is the shortest lived incandescent bulb ever, or I didn't rotate it far enough and it rattled out. At least I have my D and O/D off lights back.

 

[CharlieS]

I guess I’ll let him speak on it but if all issues are sorted, I don’t see why he would mention that above a certain RPM, the power suddenly comes back as if a switch is flipped.

My theory on this is that the ECU starts to advance the ignition as RPMs build and the jump from running to running WELL (when it advances the ignition into the "normal" range) feels like a big change from the driver's seat.

 

[CharlieS]

If it's on/off power wise I'd double check that the throttle position sensor is dialed in per the FSM.

Do you notice a difference if the PWR button for the transmission is on? Mine is always on (but the bulb is burned out) and one time it was off and I thought something was wrong.

The TPS was new last fall, and I painstakingly adjusted it when the intake and upper plenum were off recently to do injector work. It bench tested correctly, and I set the drop off with a multimeter. I took a lot of time to get it perfect.

Please ignore white paint line and awl mark, that was for the prior TPS so I could reinstall it after bench testing. The yellow paint pen is to idiot proof getting the connector right the first time.

 

[DIRTBIKEUSA]

Could it be worn dizzy gear? Too much backlash between the cam gear?

Ecu fault? Hmm not sure how to test for that other than a dead one or a one for one swap... Have you inspected the wire harness?

 

[CharlieS]

There doesn't feel like any backlash in the distrbutor gears. No damaged wires that I have observed with a visual inspection, and no codes or other errant behaviors.

I actually have a spare ECU that I could try, but for pragmatic reasons, I think I'm going to pause my efforts.

 

[CharlieS]

Hi all. Thank you so much for all the input, information, ideas and advice.

I've run out of time so I'm going to let this one ride until I get back from a trip. We'll give it some good testing both in transit and offroad.

Everything is running great at the (assumed to be fictional) 24 degrees of advance, despite marks not lining up with the crank pulley notch and timing marks on the block.

I'll keep my new adjustable timing light, 30mm, 12mm and 8 mm sockets handy in my onboard tool kit. I've gotten very quick at removing the distributor after all this practice. If it wasn't for that lower bolt on the distributor cap, I could have it off in a minute flat.

Thanks again, and I will definitely unearth this thread if I figure out what the root cause is. Nobody likes a cliffhanger ending.

 

[DIRTBIKEUSA]

Hi all. Thank you so much for all the input, information, ideas and advice.

I've run out of time so I'm going to let this one ride until I get back from a trip. We'll give it some good testing both in transit and offroad.

Everything is running great at the (assumed to be fictional) 24 degrees of advance, despite marks not lining up with the crank pulley notch and timing marks on the block.

I'll keep my new adjustable timing light, 30mm, 12mm and 8 mm sockets handy in my onboard tool kit. I've gotten very quick at removing the distributor after all this practice. If it wasn't for that lower bolt on the distributor cap, I could have it off in a minute flat.

Thanks again, and I will definitely unearth this thread if I figure out what the root cause is. Nobody likes a cliffhanger ending.

And then we wait..j/k

 

[Marvelicious]

The math for being one tooth off certainly adds up. 24-18=6* where he's saying it's running good. Meanwhile, trying for the factory 3* setting would have it sitting at 15* AFTER TDC... which would probably want to choke until the revs get up to the point where the system dials in some advance.

I'm running stock gears and 35" rubber too, and while it's no racecar, it doesn't ever try to die.

 

[BILT4ME]

Is the rubber in your Harmonic balancer damaged and the outer ring slipped in place so it does not show an accurate location anymore? If it's running well, and the timing marks are that far off, that's the only other solution.

 

[SNLC]

First of all, thank you all for the ideas and suggestions.

I'm not in overdrive, and the compression is good.

I agree that tires can have a significant impact, but in this case, since I can completely dial it out with timing adjustments, I am confident that I'm chasing an ignition timing issue.

More as I fine tune.

Here is mine,



New engine (not rebuilt, new) 16,000 miles ago. Stock gears and 315’s. 2,500ft in elevation and no other real mods to speak of.

Cheers