lack of power after head replacement, 1990 2.3l

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nico
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lack of power after head replacement, 1990 2.3l

Postby nico » Tue Apr 25, 2017 5:42 pm

finally got around to replacing cracked head after truck sat idle for 3 years. replacement head came off running vehicle. Issue: truck starts up fine, but has lack of power. compression check showed minimum of 120lbs on all cyls. exhaust has very unburnt fuel smell and plugs have dry black buildup on them. adjusting timing does not seem to effect issue. any advice on this would be great. truck is in great shape and only 100k miles on it.

oldestisuzuist
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Re: lack of power after head replacement, 1990 2.3l

Postby oldestisuzuist » Wed Apr 26, 2017 9:24 am

Valves adjusted properly?
What was the compression like with the old head?
When the donor head was on the "running vehicle" what was it running like? Any of the same symptoms you are experiencing since the head change?
'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, body ROUGH, bought new 12/4/78. A pre-P'up?
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch.

nico
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Re: lack of power after head replacement, 1990 2.3l

Postby nico » Wed Apr 26, 2017 1:29 pm

I have not checked the valve adjustment, I will do that now at your suggestion. I never had to do a compression check on old head. The only symptom the donor engine had that I am aware of is it smoke at little.

oldestisuzuist
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Re: lack of power after head replacement, 1990 2.3l

Postby oldestisuzuist » Thu Apr 27, 2017 8:31 am

If you didn't do a wet & dry compression test do that before & after the valve adjust & report the results.
Valves adjust cold (sitting overnight cold), .006"intake/.010"exhaust.
'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, body ROUGH, bought new 12/4/78. A pre-P'up?
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch.

nico
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Re: lack of power after head replacement, 1990 2.3l

Postby nico » Thu Apr 27, 2017 2:30 pm

will do, thanks

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Re: lack of power after head replacement, 1990 2.3l

Postby Red Truck » Thu Apr 27, 2017 2:43 pm

Couldn't help to toss in my 2 cents: based on the operation you've just completed, I'd double-check the valve timing once more. If it's off one or maybe two teeth, it may exhibit the symptoms you have. This forum is loaded with guidance on the subject, if you need it.
'87 Isuzu pickup 2.3 gas, 5spd, 4WD

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Re: lack of power after head replacement, 1990 2.3l

Postby puttputtinpup » Thu Apr 27, 2017 3:49 pm

I agree w red truck

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Re: lack of power after head replacement, 1990 2.3l

Postby bushwill » Sat May 06, 2017 12:06 pm

Ok fellas looking for some info.... new isuzu owner. Here's the skinny. Just bought a 92 puckup 2.3 5 sp with no power options. Truck has less than 50k miles. It sat for a few years. I replaced carb. All tuneup components cap rotor button, and coil. It starts runs and drives. It however runs rough. Actually only on cylinders 3 & 4 only. I checked dry compression as seemed to be low at about 95 each cylinder, but all within a couple pounds.when it's running I can pull both 1 & 2 plug wires as nothing changes. Plugs 1 & 2 are clean and doest seem to be burning. Any wisdom before I pull the head? I turn the motor by hand and hear the exhaust valves open letting air escape. But nothing on first two.

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Re: lack of power after head replacement, 1990 2.3l

Postby puttputtinpup » Sat May 06, 2017 10:11 pm

bushwill wrote:Ok fellas looking for some info.... new isuzu owner. Here's the skinny. Just bought a 92 puckup 2.3 5 sp with no power options. Truck has less than 50k miles. It sat for a few years. I replaced carb. All tuneup components cap rotor button, and coil. It starts runs and drives. It however runs rough. Actually only on cylinders 3 & 4 only. I checked dry compression as seemed to be low at about 95 each cylinder, but all within a couple pounds.when it's running I can pull both 1 & 2 plug wires as nothing changes. Plugs 1 & 2 are clean and doest seem to be burning. Any wisdom before I pull the head? I turn the motor by hand and hear the exhaust valves open letting air escape. But nothing on first two.
we'd love to have you join in on this topic but this thread as we call it belongs to the original author.

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Re: lack of power after head replacement, 1990 2.3l

Postby nico » Sun May 28, 2017 7:47 am

hey guys, took awhile to get back. life gets in the way sometimes. Anyway I did the wet and dry compression check. all cyls checked at 140-145lbs both wet and dry, so I don't think stuck rings or valves are my issue. As to red trucks suggestion, early on when I first got truck stated again and this problem occurred I did inspect cam/crank timing and reset it.
I have not checked the valve settings as yet, that will be a task for later this week.
Thanks for the help!

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puttputtinpup
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Re: lack of power after head replacement, 1990 2.3l

Postby puttputtinpup » Sun May 28, 2017 8:44 am

Would this have the Hitachi carb on it? Are the secondary s opening up? Take breather off. Have it running, open half throttle then manually open up secondary barrel. It should take off like a scalded dog. They operate, I believe, by vacuum trough a passageway from under the carb through the body to the top where the diaphragm for the secondary is mounted. If there's a leak, it won't open when needed and engine runs lean

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Re: lack of power after head replacement, 1990 2.3l

Postby Red Truck » Fri Jun 02, 2017 10:22 am

Might it be a crossed plug wire? That may explain your plug condition and lack of power (firing on the exhaust stroke), and it sounds like everything else checks out. Just thinking what would be affected after removing/replacing the head.
'87 Isuzu pickup 2.3 gas, 5spd, 4WD

nico
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Re: lack of power after head replacement, 1990 2.3l

Postby nico » Sat Sep 15, 2018 10:12 am

been a while since I've been on. I did get the truck running well after I realized it times off #4 cylinder and not #1 when installing distributor. It was running decent enough that I was about to make it my every day driver until.....The engine had a slight idle stumble so before I started driving regular I thought i'd repair some of the cracked vacuum lines. What a mistake! I was very careful to do 1 line at a time and referenced the diagram on hood, but now the truck tends to run at high rpm but not consistant, also is running very rich (black gas smelling exhaust) I have not touched the fuel/air mixture adjustment. It did not run rich until vac lines replaced

The ERG is operating, PVC line is drawing Vac, No change if I unplug Thermo valve, timing adjust no effect, unplugging MCV no real effect, The throttle adjust screw backed all the way off,Cable is not binding, Idle adjust screw does not seem to do anything, Does not make much difference if breather lines are connected or not. Checked for other vacuum leaks-none found, As I stated, it ran well until vac lines replace.