Doggy low rpm, but plenty of juice over 2k rpm

[CharlieS]

I'm chasing a problem which I've largely ignored and wanted to pick the collective brain on it.

Background is that this is a '94 with just over 300k miles. I bought it last year and have been chipping away at baselining it since.

When I first step on it from a dead stop, it bogs down, then I experience very doggy acceleration off the line and until rpms get up over 2k rpms - especially noticeable when it is very cold, but even after it warms up. Over 2 K rpm it runs amazing!

It feels like something is retarding the ignition or it is starved for fuel or air until the rpms get above 2k. When it kicks in, it is like a switch, vaguely like a turbo or variable cam kicking in.

I've done a lot of maintenance, and will absolutely fail to mention something here, sorry about that. I replaced every bit (no exaggeration) of rubber in the engine bay (including intake boot, valve cover gasket and spark plug seals), new fuel filter, air filter, oil filter, plugs, wires, cap, rotor, fuel pressure regulator, fuel pump relay, fuel pump resistor, rebuilt injectors, new pigtails and connectors for injectors, pcv replaced, ecu temp sensor replaced, no burned wires in the harness near (former) egr pipe, replaced IAC and TPS, rebuilt/balanced injectors with new seals, no vaccum leaks (smoke tested). EGR and Pair removed. New radiator and coolant. New O2 sensors. Thermostat and water pump replaced. New alternator. VSV for fuel pressure (tested functional) is the only VSV present.

Idles like a top at 650 +/- 50, idles up with AC, accelerates well over 2k rpm. As well or better than I have come to expect from any 1FZFE.

i just checked it and timing is around 7 degrees (I know stock is 3 degrees - but that makes it worse) with the jumper, engine warmed up.

No (OBDI) codes stored. No check engine light.

I changed the fuel filter, but I have never touched the fuel pump assembly and am wondering if an old clogged fuel strainer sock could cause this kind of thing? If it is like the rest of the vehicle it is probably original equipment with 300k on it.

I've also never toughed the knock sensors and wonder if they might be retarding timing. I'll have to see if there is a bench test in the fsm...

I have a fresh pump (denso for a v8 4runner) to go in, that I could swap in, but I'm leery of just throwing parts at an issue.

I should mention that I am running 35s with stock gears and stock transfer (I have sumo transfer gears that I still need to install) that might be relevant to doggy acceleration...?

Thanks in advance for any theories, guidance, advice or anecdotes.

 

[80t0ylc]

I would be willing to suggest it's your 35's with stock gears. Not on a highway, but on a side street with little to no traffic, put it in low range and try your acceleration and see if you experience the same doggy performance.

 

[CharlieS]

I would be willing to suggest it's your 35's with stock gears. Not on a highway, but on a side street with little to no traffic, put it in low range and try your acceleration and see if you experience the same doggy performance.

Luckily where I live there are lots of remote dirt roads.

In low gear, no lag or doggyness whatsoever. Linear power delivery from idle to 3k rpm. Looks like I need to accelerate my gear project. Thank you!

 

[80t0ylc]

Believe me, over the period of ownership - since 1999 to now, going from stock 31's to 33's and eventually 35's, my 5.29 gears were the best performance enhancer for me. I also run 35's and it was suggested to me by Zuk (gearinstalls.com) who installed the gears and Harrop's e-lockers, since I also tow an off road trailer, to go with the 5.29's instead of the 4.88's I was originally wanting. Transfer case is probably a better choice, but since the 3rds were already out, it was a perfect time to do it and not a bad choice, IMHO.

 

[CharlieS]

I would definitely regear at the differentials if I was going in to do lockers, but I got this with the lockers already installed and the PO, and for whatever reason, they opted to stick with stock gearing (probably cost...).

Since I am going into the transfer case to do the low gear already, I figured it is a good time to do the high gear too. I'm hoping that is good enough, but if not, I'll eventually regear the diffs too.

It is so weird that this feels like the engine struggling, but I guess all that mass and inertia from the tires just makes it feel that way.

 

[baldilocks]

Have you confirmed VAFM condition and performance? I’ve read posts where they check out on the bench but ended up being the culprit anyway.

 

[CharlieS]

I have, and the one in the rig now is actually a used factory one I bought used from a mud vendor. So I have both the working original and this backup.

Also, forgot to mention I painstakingly adjusted the TPS by multimeter when the manifold was out to get it perfect by the book. What a PITA to get it just right...

 

[80t0ylc]

It is so weird that this feels like the engine struggling, but I guess all that mass and inertia from the tires just makes it feel that way.

Yep, we're not talking about pushing aluminum and plastic An overbuilt rig with steel bumpers, sliders, skid plates, aux fuel tanks and any other armor doesn't help with OEM gear ratios - not to mention bigger tires. I don't know about yours but my '94 tips the scales around 7200 lbs, and that's with the original non turbo 1FZ.

 

[TurbodreamZ]

From your description of the problem, it doesn’t sound like a gearing issue. I’m been dealing with the same issue on my stock LX450.

Mine “stumbles” or “hesitates” between idle and ~2500rpm. Above that, it runs and pulls like brand new. Under that, the more throttle you give, the worse it runs.

I’ve read a bunch of threads which describe the issue but everyone seems to have a different solution.

yours isn’t throwing codes yet but I bet something will trigger it when the problem gets worse. Mine threw a lean bank 1 code and eventually the cyl 1 injector died.

i wish I could single out the issue one item at a time but I don’t have the time to do so. I have a bunch of new oem parts that I’m about to throw at it. They are the following:

1. 6x new oem injectors
2. Fuel pressure regulator
3. New gaskets for intake/ throttle body

If that doesn’t work, I also have he following on hand:

4.new oem fuel pump
5. Fuel pump resistor
6. Fuel pump relay

 

[CharlieS]

Have you confirmed VAFM condition and performance? I’ve read posts where they check out on the bench but ended up being the culprit anyway.

For a comparison I swapped in my original VAF and the behavior was the same.

 

[CharlieS]

Yep, we're not talking about pushing aluminum and plastic An overbuilt rig with steel bumpers, sliders, skid plates, aux fuel tanks and any other armor doesn't help with OEM gear ratios - not to mention bigger tires. I don't know about yours but my '94 tips the scales around 7200 lbs, and that's with the original non turbo 1FZ.

Yep, front and rear steel bumpers, winch, sliders, xfer skid. It's the typical build around here. No lightweight!

 

[baldilocks]

Perhaps the new fuel pressure regulator is either defective or it’s not receiving the vacuum signal to increase FP appropriately? Maybe swap in the old reg and resistor if you still have them. It does sound like a fuel delivery issue.

How does the engine rev when in Park of Neutral?

 

[80t0ylc]

From your description of the problem, it doesn’t sound like a gearing issue. I’m been dealing with the same issue on my stock LX450.

Mine “stumbles” or “hesitates” between idle and ~2500rpm. Above that, it runs and pulls like brand new. Under that, the more throttle you give, the worse it runs.

I’ve read a bunch of threads which describe the issue but everyone seems to have a different solution.

yours isn’t throwing codes yet but I bet something will trigger it when the problem gets worse. Mine threw a lean bank 1 code and eventually the cyl 1 injector died.

i wish I could single out the issue one item at a time but I don’t have the time to do so. I have a bunch of new oem parts that I’m about to throw at it. They are the following:

1. 6x new oem injectors
2. Fuel pressure regulator
3. New gaskets for intake/ throttle body

If that doesn’t work, I also have he following on hand:

4.new oem fuel pump
5. Fuel pump resistor
6. Fuel pump relay

Charlie never mentioned any rough running or stumbling - just doggy performance. And he had pretty much gone through the engine. That's exactly why I suggested gearing. I had read most of the way through his original post in this thread and near the end he mentioned 35's and stock gears. It then clicked, I'd seen this - ever since I went with bigger tires. Started somewhat with the 33's. Then I went to 35's and I just couldn't live with it anymore. 1st time I took it for a test drive when I got it back together after the axle rebuild, it was like - I got the power back! Pavement or off road - either was back to par - or actually better IMHO.

 

[CharlieS]

All rough running, idling and similar issues have been sorted. Generally speaking, it runs like a top.

I'll mess around with the FPR and resistor tomorrow. I saved both of them. Definitely worth a try.

Hearing @80t0ylc s experience sounds like it very well could be my issue, but I'm definitely up for trying to tackle it multiple ways. Maybe I have a couple of things combining to make it more pronounced.

 

[TurbodreamZ]

Charlie never mentioned any rough running or stumbling - just doggy performance. And he had pretty much gone through the engine. That's exactly why I suggested gearing. I had read most of the way through his original post in this thread and near the end he mentioned 35's and stock gears. It then clicked, I'd seen this - ever since I went with bigger tires. Started somewhat with the 33's. Then I went to 35's and I just couldn't live with it anymore. 1st time I took it for a test drive when I got it back together after the axle rebuild, it was like - I got the power back! Pavement or off road - either was back to par - or actually better IMHO.

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. Big tires are not going to cause you to lose a significant noticeable amount of power between 2,000 And 2,100 rpm. As he stated in the first post, it feels like turbo or VVT kicking in. This is exactly how I would describe my issue. I’d say I’m losing more than half HP When mine did this. Above a certain rpm I am thrown back in my seat and the revs are smooth to redline.

To me there is clearly something wrong with fuel/timing or something along those lines but I will be watching this thread because I have the same issue with stock wheels/tires.

I would have made a video of mine having the same issue but I already started tearing it down. If OP could make a video that would be helpful.

 

[ppc]

I would monitor the fuel pump voltage on the "FP" terminal on the diagnostic connector to see if the kick in performance corresponds to a rise in voltage to the pump. This would point to a failing fuel pump or clogged strainer/filter in the tank.

 

[CharlieS]

I think I may be onto another self inflicted problem.

I've been messing around with ignition timing all morning, and what I found is that it accelerates from a stop like crap everywhere from 3-15 degrees, BUT if I move the static timing off the marks to the left/passenger side to what must be around 20 degrees it has gobs of power off the line.

I wonder if I reinstalled my distributor off by a tooth? I followed the FSM assembly procedure when I did my valve cover gasket, spark plug seals and distributor o-ring, but I absolutely could have messed up.

Is there a way to line up the distributor adjusting it by a tooth without taking the valve cover off and seeing the marks on the timing gear?

 

[TurbodreamZ]

I think I may be onto another self inflicted problem.

I've been messing around with ignition timing all morning, and what I found is that it accelerates from a stop like crap everywhere from 3-15 degrees, BUT if I move the static timing off the marks to the left/passenger side to what must be around 20 degrees it has gobs of power off the line.

I wonder if I reinstalled my distributor off by a tooth? I followed the FSM assembly procedure when I did my valve cover gasket, spark plug seals and distributor o-ring, but I absolutely could have messed up.

Is there a way to line up the distributor adjusting it by a tooth without taking the valve cover off and seeing the marks on the timing gear?

FJ80 Distributor - How to install

Greetings Gents, I have a distributor to put in. The service manual says to align camshafts to double dots and balancer pulley to 0 degrees. It then states to align notches on the distributor and plug it in. I have two questions: 1. The distributor rotates while being pushed in, due to the...

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[BILT4ME]

I think I may be onto another self inflicted problem.

I've been messing around with ignition timing all morning, and what I found is that it accelerates from a stop like crap everywhere from 3-15 degrees, BUT if I move the static timing off the marks to the left/passenger side to what must be around 20 degrees it has gobs of power off the line.

I wonder if I reinstalled my distributor off by a tooth? I followed the FSM assembly procedure when I did my valve cover gasket, spark plug seals and distributor o-ring, but I absolutely could have messed up.

Is there a way to line up the distributor adjusting it by a tooth without taking the valve cover off and seeing the marks on the timing gear?

Yes.

Pull the cap and note where the rotor is located (straight on, I use a photo) also note the bolt location in the slot for timing rotation, then pull the dizzy just enough to disengage the teeth, rotate the rotor one tooth in the direction you want to adjust, then reinsert and reassemble. No need to pull to TDC and dll that unless you screw it up, then you have start over and set it at TDC. No, you still don't have to pull the VC to check it even then.
If you check the FSM, there are notches and circles that will line up the timing marks on the dizzy when you have it at TDC.

FYI proper timing the bolt is about perfect center of the slot.

 

[baldilocks]

The adjustment slot of the distributor allows enough room to adjust out a one tooth off condition. I reckon yours is off more than one tooth. The last 80 I bought was off by a tooth but ran very well. The only reason I knew it was off was because the lock down bolt was way off center of the adjustment slot which I had learned from a previous cruiser HG job. You might be well served to start from scratch.