Loss of power on high speed or under load

[astro49]

need your opinions guys. my 4jb1 mu just lost it power and acceleration lately. though it runs quite normal while driving slowly and smoothly on city driving, it has dramatically lost its power while accelerating and under load. i first noticed this when i went off roading last week and there this quite long stretch of uphill that i usually negotiate using only the drive position on my matic transmission. now there's a lot of power lost and used the 2 and L position just to climb that mountain. before that off road trecking, i've been playing around with my injection pumps timing. advanced it quite a bit (my marker is the distance of the injection pumps diaphram and the lower portion of the intake manifold. i'd say my settings now is not quite far from the original settings (though more on the advanced side). i also noticed that my turbo pressure has dropped from my normal 12psi to 9-10 psi (have a turbo regulator installed). my turbo still whines as before. and even took of the hose from the outlet side of the turbo just to check and see if the turbo is working or spinning, and it looks fine. can this be a sticking or open waste gate???

btw, my engine emits more black smoke now than before this loss of speed probem started.

also, just replaced my fuel filter just to isolate the problem but no improvement still

[astro49]

more questions..
1. can a retarded or advanced timing cause a decline of turbo pressure
also
2. can a lean or rich mixture affect turbo pressure, in my case a drop of 2-3 psi? (i've be playing with my mixture screw too)

** just trying to isolate and pinpoint my loss of power problem

[astro49]

what is that black round can (and its function) which looks like a diaphram? its on the left side of the turbo. it has a small tubing for either pressure (or vacuum). I'm not referring to the diaphram which actuates the waste gate

foto picked up from james w site, THANKS!

[James W]

That diaphram operates the exhaust restrictor for the engine quick warm up system. It is vacume operated. Maybe it's jammed or loose?

[astro49]

Thanks for that information James!
When you say its for quick engine warm up, is this more functional and ideal for cold weather situations? I live in the tropics (Manila) and was thinking if I can disable this (plug the vacuum hose or better yet, take off that diaphram) so less things that could go wrong and cause problems? Similar to what I did with my EGRs which were the culprit when my MU before also lost some power and smoke belched a lot.

[James W]

The quick warm up system only comes on if you have the switch on the dash on and it's cold enough. About 5 Deg C? Somewhere around there in temperature. The sensor in front of the radiator? So yes I suspect you don't have much need for it. You could also remove the restrictor from the exhaust to make it more free flow.

[geeves]

the temp sender is the wire at the right hand side (drivers) side of the thermost housing. Remove this and the glow plugs stay on 30 sec as well. Also advances the timing causing diesel knock.

[astro49]

jamesw said:

The quick warm up system only comes on if you have the switch on the dash on and it's cold enough. About 5 Deg C? Somewhere around there in temperature. The sensor in front of the radiator? So yes I suspect you don't have much need for it. You could also remove the restrictor from the exhaust to make it more free flow.

Do you mean the quick warm up system is manually activated by that switch (beside the fog lamp and defogger switches)? I tried switching that ON before. Isn't it supposed to light up indicating its on? Well mine doesn't light up so I never did use or activate that switch.

I'm now a bit confused hehehe. Does that switch have anything to do with that diaphragm I was referring to earlier? Or is only for for the prolonged TURN ON time of the glow plugs? Does that switch also activate a solenoid switch which activates the vacuum line leading to that exhaust diaphragm?

What I now did was plug that vacuum hose which leads to the that exhaust diaphragm. There seemed to be some slight improvement in engine response and power.

However, since I am also suspecting the cause of loss of power might be coming from the turbo o leaky waste gate, I experimented on plugging the hose coming from turbo which leads to the waste gate (thus also removing the turbo regulator). Unfortunately, my boost pressure still was 9-10psi only. While before this problem happened the pressure was 12-13 lbs. Without that pressure hose leading to the waste gate, shouldn't the pressure shoot up to around or more that 15lbs?

Sorry mods for the countless questions and much appreciated for your patience in answering them!

[James W]

Perhaps you have one or more sensors faulty. It looks to me the two sensors are in series. One the ambinat air sensor in front of the radiator (I think? ) and the other in the theromstat housing. I have had one of these goe faulty before. There is a test procedure.
Yes the switch should light up, but only when cold enough. Check out this link and see if if helps you at all;
jamesw.kicks-ass.net/4wd/TF4JE-WE-9791_Page292-295.pdf

What status is the butterfly valve on top of the engine after the turbo and before the intake manifold? Usually has "Isuszu 2800" or simular on it.

[Les]

im guessing you are running a boost gauge, check connections on your hose fittings carefully if there is a leak any were this will affect turbo boost. Also if you have fuel mixture screw two rich boost will drop off it may be worth setting timing and fuel mix back to where it origonally was and see if theres any improvement. I suspect your problem is a simple one. Also did you remove egrs of manifiold worth checking that theres not an air leak there.

[astro49]

@james W, geeves and Les

Thanks a lot for all your suggestions and recommendations, really appreciate you guys helping out!

Well looks like I got lucky this afternoon! After removing that rusty vacuum diaphragm, I finally found out that it was that exhaust restrictor that links to that vacuum diaphragm was the culprit! It was resting 1/4 open. And while I tried swinging the spring loaded lever which actuates the butterfly of that restrictor to open and close, there indeed was a portion that was hard to move. Maybe it was corroded with rust or had a lot of exhaust residue. What I did was just leave it without the lever from the diaphragm and into the position where the spring on its lever was at its most extended state.

After doing the above, I now took the MU for a spin. And since I took off earlier and plugged w/ a metal screw the hose from the turbo that leads to the waste gate, my turbo pressure gauge now read 14-15 psi (under acceleration and uphill)!!! Acceleration is now back to normal and black smoke has been minimized too. Its again fun to drive my MU.

Btw, when I removed and plugged the EGR pipe and its 2 diaphragms about 2 months ago, I also removed that butterly after the turbo and before the aluminum pipe which reads Turbo 2800 since that already has caused some problems before when it stuck in closed position and resulted in very much loss of power with lots of black smoke.

Very tempting now to leave the waste gate pressure hose plugged because of the 14-15lb boost it now gets (with a dash of richer diesel mixture) but I might end up with broken rings or blown head gaskets so its wiser to throw in again that boost regulator and limit the boost to maybe around 12lbs.

Thanks again guys for all your ideas and help!! More power to Club Isuzu.com

[roscoe46956]

Gday Astro, Just noticed this thread, the symtoms you descibed are classic for a restricted air cleaner.
Remove the element and go for a drive(you wont hurt the engine for the short time you are trying it)

It may be something else but always rule out the simple things first

Cheers mate

Roscoe

[astro49]

Good Evenning roscoe46956!

Thanks for that advise!

I actually did take off the air cleaner for a whole day (actually forgot it was out hehehe) soon after the engine lost its power. Then also replaced and suspected the fuel filter since it was quite an effort priming the fuel even with the fuel line that leads to the injection pump was removed.

[Les]

Hi again astro
if u run boost to high its worth remembering that theres an overboost valve in your manifold and this will open up and dump pressure back into the nlet via the pipe that also acts as engine breather from tappit cover i got caught out with this one it ended up damaging the diaphram in tappit cover that acts as pcv valve of sorts my oil useage went up dramatically thought i had damaged engine for a bit
cheers Les

[astro49]

Thanks for that info Les! I'll keep that in mind and monitor my blow out valve while my boost is still now between 13-14 psi

[geeves]

Thats where mine is running so should be ok. The Mus sometimes run the blow off valve as a separate pipe back to the air cleaner. This could be a worthwhile mod

[Les]

geeves thats a real good thought i did put a different pcv valve in my one but i will run the blow off valve into my aor cleaner as well thanks for that one
cheers Les

[astro49]

geeves.. Thanks again for the advise. I'm confident with your experience and authority with Isuzus, I can now get away with that high boost level!

Thanks again to everyone who's contributed with this thread!

My MU now really is fun to drive since I got it 6 months ago. With the higher turbo boost, advanced timing and richer diesel mixture (plus Rancho 9000s), its runs and rides a lot more responsive and effortless! Thanks too to Club Isuzu.com. I have learned a lot from this club.

Next project.. but ofcourse the 2.5" exhaust pipe after the flexible pipe. Have a 3"Fujitsuba racing straight through muffler (got from surplus Nissan Skyline JDM) that I plan to use. Hope it too could add a few more horses.