Hard cold start - possibly down on power - help!

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fen
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Re: Hard cold start - possibly down on power - help!

Post by fen »

Halden wrote: Fri Dec 13, 2024 5:34 pm How good is your compression? It seems like you've got your timing dialed in, and the CSD defaults to advancing the timing, unless somehow it's stuck off which would be unusual... Have you checked your valve lash? That can have a huge impact. Especially if you don't compensate for the wear on the rockers. Even my truck with crappy compression at altitude starts relatively easily in the winter, and I got rid of the CSD on it.



How bad is your compression?

I had

Compression Test video:
https://www.youtube.com/watch?v=Jn-Lgf6CiOk

Results:
#1 ~370
#2 ~400
#3 ~370
#4 ~350


I did try doing a valve lash adjustment but did not notice much difference if any. Did not look at wear on rockers though.

I did have a CSD issue causing low power at speed but I rebuilt that.

Honestly I think it’s just a Smokey engine with lots of blow by and not great enough compression to cold start without help.

My guess is ether use by the shop put it over the edge after they fully advanced the timing.
'81 P’up 2.2L diesel dlx 5-speed 2wd short bed
‘93 Chevy G20 6.5L Diesel
'82 diesel Chevette (Isuzu 1.8L 4FB1) 4 door 5-speed
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jacktwease
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Re: Hard cold start - possibly down on power - help!

Post by jacktwease »

ive been referencing this thread and others in the forum with my last few months of hard start trouble shooting.

my problems were a starter that was slowly going bad... and a disconnected wire at the very back of the glow plug rail hidden by the oil filter. It was starting with the long glow cycle but now that I fixed the back wire it fires up easy on the quick normal cycle. maybe not your issue but felt like posting.
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Re: Hard cold start - possibly down on power - help!

Post by isuzu Specialities »

Cranking over the engine until max pressure is obtained is not the proper prosudure for a compression test. These test results are invalid as they do not indicate anything about the condition of your engine.

This is a common mistake made by all novice who perform this test. I've done it myself many years ago when I started my career.

A compression tester set like you have is used to facilitate multiple symptom based diagnostic test. All aimed at determining overall health of a engine or pin pointing a specific operating fault. Out of the 5 test that can be performed by this tool not one requires cranking over the engine over and over & over.

You're experiencing a hard start & loss of power symptom.
For the age of your engine the test you should be performing is the One-Over-Five test.

Here is how to perform this test...
Prep by
#1 shut the fuel off,
#2 remove the air filter & cleaner assembly.
#3 fix the throttle valve so it remains open at all times.
#3 remove all the glow plugs.
#4 place the compress tester gauge where you can see it when cranking over the engine.
#5 verify the battery is good & fully charged.
Optional #6 connect a jumper wire or remote starter button to the starter solenoid so you can activate the starter without leaving the front of the vehicle.


Performing the test....
Connect the tester to cylinder 1. While watching the gauge crank the engine until one cycle is complete. Pay attention to how the pointer acts when the cylinder pumps up.
Record this number. If the pointer stops then moves again record that min/max valve. If the needle goes up & drops a bit then settles record the high and low and note it's action.
If the pointer pumps up one time and stays at that value this is called true static compression & this is what you want to see. Record this number & circle it.

Next move along to the other cylinders the same way. When you done all 4 cylinders like this it's time to start the second half of the test.... "Over 5"

With the tester connect to cylinder #1.
Crank the engine over for 5 cycles. Watch the pointer actions. Each of the 5 pumps the pointer should only increase. After the 5th pump record that pressure valve beside the first test valve. Move along to the remaining cylinders.

Why this way?
For about 1/2 of the first compression stroke there is no pressure applied to the piston rings, piston & valves. For this amount of time air is blowing by these parts. Until the increase in pressure becomes so high it forces these parts to seal. The first pump valve you recorded is testing how well your cylinder traps air inside. Ideally you want these number high. However it's most important that they be even. Any variation more than 15% indicates a loss of the engines the ability to idle smoothly and start quickly. Anything over at or over 20% difference a leak down test is required to identify the source of the loss. If all cylinders are low but even indicates a running engine that is simply tired.

The 5th pump.....
Why only 5 pumps? If the engine has lost its ability to come to max cylinder pressure by the 5 pump ..the engine will never run correctly & requires major repair. A leak down test is required to pin point the source of the loss.
All pressure recordings on the 5th pump ideally should be high. The numbers should be no more than 20% difference between cylinders to cylinder. Again most importantly the numbers should be even. If all cylinders are near 20% or even a little bit over but even. Your engine is simply just worn out and tired.
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fen
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Re: Hard cold start - possibly down on power - help!

Post by fen »

jacktwease wrote: Sat Jan 11, 2025 9:14 pm my problems were a starter that was slowly going bad... and a disconnected wire at the very back of the glow plug rail hidden by the oil filter. It was starting with the long glow cycle but now that I fixed the back wire it fires up easy on the quick normal cycle. maybe not your issue but felt like posting.
Good info. My starter cranks well enough especially with new/fully charged battery. I did have an issue with that wire in the past I believe too.
'81 P’up 2.2L diesel dlx 5-speed 2wd short bed
‘93 Chevy G20 6.5L Diesel
'82 diesel Chevette (Isuzu 1.8L 4FB1) 4 door 5-speed
'99 Isuzu VehiCROSS 3.5L
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fen
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Re: Hard cold start - possibly down on power - help!

Post by fen »

isuzu Specialities wrote: Sun Jan 12, 2025 4:42 am Cranking over the engine until max pressure is obtained is not the proper prosudure for a compression test. These test results are invalid as they do not indicate anything about the condition of your engine.
It seems that the test I did is just an extension of the 5 test? Perhaps giving a few more pumps. Cranking further usually didn’t seem to increase the psi much but it could mean that the results I’d get from the 5 method are slightly lower than what I indicated.

A test result for one pump does seem like it would be interesting.

I believe I left the glow plugs in and replaced one at a time with the compression tester. Not sure what difference that would make over removing all of them.
'81 P’up 2.2L diesel dlx 5-speed 2wd short bed
‘93 Chevy G20 6.5L Diesel
'82 diesel Chevette (Isuzu 1.8L 4FB1) 4 door 5-speed
'99 Isuzu VehiCROSS 3.5L
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Re: Hard cold start - possibly down on power - help!

Post by Halden »

fen wrote: Fri Jan 17, 2025 10:16 am
It seems that the test I did is just an extension of the 5 test? Perhaps giving a few more pumps. Cranking further usually didn’t seem to increase the psi much but it could mean that the results I’d get from the 5 method are slightly lower than what I indicated.

A test result for one pump does seem like it would be interesting.

I believe I left the glow plugs in and replaced one at a time with the compression tester. Not sure what difference that would make over removing all of them.
Last time I did a test with a gauge it looked like crap. I think I was in the mid-300s or something, but that truck runs pretty good other than a fuel issue from neglect at the moment.

It looks like number 4 is getting to be on the outskirts of allowable deviance. What I don't like about using a gauge to judge how good the compression is: Altitude, battery, rpm and air filter restriction play a huge roll in your score. For all we know maybe you were spinning just a little slower by the end of your test. It doesn't take much loss in speed to get a noticeably worse reading. Do you know what your cranking speed is?

In my experience with compression tests you really don't want to do more than 5-8 compression strokes using a gauge, the reason being eventually that reading will get high enough to pass. Personally, I stick an o-scope with a current clamp and look at the variation in current after the starter gets up to speed. It's more accurate since you don't drain your battery down testing all cylinder individually. All automotive OEM's look at this as a valid compression test. Being a mechanical engine there is no clean/easy way to correlate which current peak to which cylinder.

Really if you want to get into the nitty-gritty you would do a leak down test. That really tells you a lot more about what's going wrong, plenty of vids on youtube to show you how to do it.
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