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I posted here in Honda because there is no section for an Isuzu. I have an 1999 Amigo which is the same as the Honda Passport. The problem I am having is this:
I just purchased this car with a friend and a little project. I have managed to make all of the repairs except for this. The car idles rough and is very short on power. When it is at an idle and you floor it (in neutral) it seems somewhat starved for fuel. It revs up very slowly. The best thing I can compare it to is an old carbureted engine with a bad accelerator pump. I also had a check engine light when I first got the car indicating multiple misfires. When I reset the light, it has not come back on. I have driven about 200 miles and it is still off.
So far I have checked the compression. It is 120-/+ in all 6 cylinders.
Fuel pressure is about 40lbs at an idle and if I accelerate it drops. While at an idle, I remove the vacuum line from the regulator and there is no change in pressure. If I pinch off the return line the pressure jumps dramatically. After changing the pressure regulator there is no difference. Since the pressure jumps I am assuming the fuel pump is good. The filter is new.
The plugs are all good.
Injectors were removed and checked. All have good flow and are clean.
I removed the EGR valve and it appears to be closing and sealing.

My next thought is the coils. They are a little bit pricey and I would like to be sure before I do this. Is there any way to test them?

Thanks in advance.


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contributions: 1988
Images: 37
Location: Oregon
what were ALL the codes before you cleared them? If you have a scanner available check you TPS or APS (if you have it) also look at your O2 sensors to see what they say your engine is doing. You might want to check your timing belt for correct alignment. see tsb #IB00-S005 for belt installation. it is off a couple teeth it will affect driveability. also check for a clogged cat.

I wouldn't be thinking coils yet. since they are COP a bad coil would only affect one cylinder.

Alternator is charging the battery right? Low battery voltage can cause similar problems too


   
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contributions: 3
The codes I got were:
o2 sensors slow response. I had a bad exhaust leak which I repaired.
Multiple misfires which I have not been able to find a reason for but I have not seen this code since I reset.
As far as the timing belt goes, if it were off I would think this would be reflected in the compression, no?


   
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contributions: 1988
Images: 37
Location: Oregon
compression would be affected by how much the valve timing would be off. perfect would be 132.30 at sea level. 14.7 times 9 since your compression is 9 to 1. but slow O2 affect driveability. MAF sensor could be off and not set a code if your O2 sensors are slow to react. Have you driven it with a scanner attached so you can see what the fuel trims are and what the O2 sensors do when you have a lack of power?

If the O2 sensors go to the bottom, close to zero, when you are trying to accelerate you are not getting enough fuel. When you accelerate hard they should go to the top. Fuel trims should show that the vehicle is adding fuel to the normal trim. (higher trims)

plugged or partially plugged cat's can cause a lack of power too. may be ok at idle but restricting the flow when higher flow is needed during acceleration.


   
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As I said, the 02 sensor fault indicating slow response was cleared and has not come up again since I repaired the severe exhaust leak on both sides. The converters are fairly new. I removed the timing covers and it looks as if the cams are both off 2 or 3 teeth. If the compression should be 132-/+ and I am getting 120+/- I suspect this could be what is causing my problem. I am going to reset the cams tomorrow and see where it leaves me. I am thinking this was something that the previous owner was also trying to solve when he replaced the converters. I can see that the timing belt had been replaced since there were a few bolts missing from the cover and one of the covers was cracked.

Thanks so much for your help


   
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contributions: 1988
Images: 37
Location: Oregon
before you try and reset your cam timing look up proper procedure for your engine. there is a TSB from Isuzu about cam timing. If someone replaced the timing belt before, because of breakage or timing belt disruption, they may have not put the belt on correctly.

check the tsb # IB00-S005 dated feb. 2000 for 3.2 and 3.5 V6 engines.


   
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