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Low power / hesitation

5K views 57 replies 4 participants last post by  schrochem 
#1 ·
99 trooper 3.5

I have been putting off posting til I had more info because I never felt like I had this pinned down.

Main issue:
Low power/hesitation
Idles great around 800. Revs/sounds fine in park.

However, from stop and a good amount of throttle it revs then it will shake/stutter and/or kick in.

If I accelerate very slowly it will switch gears fine. Otherwise it will go well over 3000rpm before switching. During that time Very low power.

If I take a corner, it downshifts, then I accelerate, it revs high without being in gear.

Codes:
Finally got one Today. P0300

I'm posting because I finally got something that might be helpful to diagnose this. After warmup it will go into closed loop as normal. Using my obd reader Ive been checking lots of parameters. LTFT is negative (-6 and - 12) at idle or driving without TB open. Driving and accelerating, it will work its way to less negative.

Today I was driving was monitoring the fuel status. When I'd accelerate quickly or take a corner (lack of power), the system would go into open loop/deceleration fuel cut. So it stops adding enough fuel. Which makes sense on loss of power... I read that in that state it goes by a "fuel map" in the computer.

So I'm not really sure what to do next. I've done a lot of things...but most were 2 years ago then it sat. The main thing I've noticed that might be an issue is I had replaced the compressor and most a/c parts. The a/c works great. However, the clutch will slowly rotate when not engaged. So I need to increase the gap. That couldn't cause a timing issue could it.

Timing is within spec (from service manual) while idle and Rev to 2500 in park. Fuel pressure is low for what the manual says. It's 38-40. Had a new fuel pump added two years ago before sitting.

Checked coils and plugs. Some oil in there brownish soot. Not bad. Gap a little large so adjust back.

Had the fuel rail out. Individually charged and cleaned each one with a nice spray pattern.

New fuel regulator. During idle if I pull the vacuum hose it's sucking and the engine fluctuates. Back on it stabilizes.

New evap canister. New evap purge solenoid. Solenoid continously clicks. Another one I had pulses continuously but no noise.

TB, IAC, MAF all cleaned. Fresh gas after empty. Filled up. I should change the oil... MAF had correct voltage and ground. New Air filter. Radiator and coolant fine. New fuel filter. (After sitting the line right before the fuel filter had deteriorated and leaked.)

Battery was dead but easily charged back up and hasn't been a problem since.

I currently have the center console out. I mention that because the power/winter mode wire isn't connected. If that matters.

Might be some other things but I'm leaning toward a fuel pressure issue, computer issue or something to do with the compressor and/or timing.

Thanks for any help. Scott
 
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#2 ·
Yesterday I was checking the vsvs. The one by the fuel regulator and the two down on the axle. All actuated and from what I could tell all the hoses were OK.

I also revved the engine to wot while in park. At about 6k Rpm the system goes to open loop decel cut off. Is that normal?

My TPS seems fine (new). I was graphing the tps vs engine load. One screenshot has TPS increasing from 50% to 80% in about 5 seconds. Engine load stayed at 50%. Is that normal?

Thanks for any help. Scott
 
#5 ·
I updated the first post.

One thing that it always does is have trouble shifting if the throttle is accelerating "too much." If it's gradual it's fine.
I did notice it takes a second when I back out to switch from reverse to drive.
 
#6 ·
I'm running out of ideas so any help would be appreciated.
I'm leaning towards sparks and/or ignition coils.
The resistance between coil posts 1-2, 2-3 and 1-3 all have values but they are different for each coil.
Plugs looked ok. White to brown soot. Cleaned and made sure the gap is 1-1.1. There was oil present in almost all of them. Not much but there.
Egr tube is clear but I might try another Egr that I have.
 
#7 ·
I swapped out the Egr with the other one. No change. The tube inside the air intake is clear but I don't know about the one going down from the valve. Can it cause issues if not clear? Or is it hard to restrict it?
I have to go really slow from stop to not get the engine to stutter. Chop, chop, chop. What causes that symptom specifically? That always happens.
 
#9 ·
The only thing I can suggest is run a compression test on each cylinder and also check the alignment of the timing belt with the pulleys and camshaft timing marks. If the compression is low or the valve timing is incorrect the engine will not run correctly.
 
#10 ·
Last night I used my scanner to check timing. At idle and 2500rpm I got values within the service manual. But driving it was different. Look at the attached screenshots to see the scans.
When I floor it, the rpms don't kick in despite the engine revving. The timing drops off.
If I start and continue in a slow even increase, the timing goes up with Rpm no problem.
 

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#11 ·
Your scanner is showing the PCM generated ignition timing. I am referring to the mechanical crankshaft to camshaft timing. If the timing belt was replaced and the alignment of timing belt pulleys and the timing belt is wrong the engine will not run properly because the valves in one (or both) banks are not opening and closing at the correct time and the engine is low on power. Multiple fire code P0300 can be caused by incorrect valve timing.
 
#14 ·
Holy cow you're right. I totally forgot.... Attached is the statement from the work. Before the problem came about, I changed out the a/c Compressor. I can't say for sure that I didn't mess something up with the timing. I shouldn't have but I don't know.
I also had to replace the thermostat if I didn't mention that before. I started to wonder if I messed up the knock sensor or its wiring. Or some other sensor wiring.
 

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#16 ·
I am assuming the low power problem has not been there for 10 years so the timing belt to pulley alignment is not problem.

Have you ever replaced the fuel injectors?

Will the truck accelerate from a stationary position in Drive 1st gear as quickly as it does in L (Manual 1st gear)?
 
#17 ·
I did do that. As I recall it was the same hesitation. From a stop it will stumble and not move forward then a lot of the time kick into gear.
I took the covers off the top timing. When I removed the top middle bolt it started leaking coolant. See pic white arrow. I also saw a wire at the bottom that wasn't clipped. Can't tell what it's for.
 

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#20 ·
It looks like that leak is the gasket for the water pump. Would that make sense?
Also I was just poking around and noticed the power steering fluid drained out also. I don't get that. I did take the pulley off the power steering. Wouldn't think that's a problem. I haven't removed the bottom timing belt cover. I guess I need to remove the crankshaft pulley?
 
#21 ·
You have to remove the crankshaft serpentine belt pulley to remove the lower timing belt cover.

It is recommended the timing belt be replaced every 10 years or 100K miles so you should consider changing the timing belt if you have the covers off.

Did you remove the power steering pump pulley to facilitate removal of the LH timing belt cover?
 
#22 ·
Yes sir that's why I removed it. Both of the cam marks line up.
I had tested all the fuel injectors before installing. I rigged up a way to activate them and clean them. They all functioned fine. The spray was there but I couldnt control the compressor speed so I can't say if they have perfect nebulization.
As you pointed out, my water pump and timing belt were replaced in 2015. 10k miles ago.
I was just in there again and found a small spring in the area below the throttle body. No idea what it goes to. I also noticed a fray in a wire. I don't know what sensor it is (see attached). Once removed it was gunked up underneath. It's on the front of the right bank. The wiring looks to be bundled with the knock sensor.
I'm starting to have reservations about my thermostat install two years ago. I believe it was the last thing I did before this problem but I'm not sure. Then it sat for two years. Which I will note was on an angle of about 40 deg. Front down. That's my driveway.
Not sure if I should remove the intake again to check the knock sensor and thermostat?
 

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#25 ·
I didn't really find mention of it in the service manual or a part on rockauto. Not sure if mine is functional. See attached. Looks "eaten" on one side.

Do you think I should take the intake back off and check the knock sensor and thermostat? Maybe get a better look at the coolant leak.

I still don't understand why the power steering leaked. Any ideas on that one?
Thanks for the help.
 

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#26 ·
schrochem said:
I didn't really find mention of it in the service manual or a part on rockauto. Not sure if mine is functional. See attached. Looks "eaten" on one side.
I think the capacitor probably is still functional.
schrochem said:
Do you think I should take the intake back off and check the knock sensor and thermostat? Maybe get a better look at the coolant leak.
If you have a coolant leak under the intake it could be a leaking heater coolant pipe O ring that is leaking.
schrochem said:
I still don't understand why the power steering leaked. Any ideas on that one?
What kind of tool did you use to remove the power steering pump pulley?
 
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