Question on compression test

[Rumblin_440]

I have a 78 power wagon with a 400 in it. When I changed the oil it was like I was draining black gasoline outta the oil pan(smelled like varnished fuel). The truck has been a barely driven farm truck for the past 14 or so years. The mechanical fuel pump has been replaced but someone installed an inline electric pump I'm guessing before the mechanical one was replaced. The 2 barrel that I removed to swap out for a 4 barrel setup was definitely not in working order probably just drowning the cylinders.
There is a little background on my situation now for my question. When doing a compression test what kinda pressures should I be looking for roughly I know the numbers aren't a huge deal just mainly that they are all similar.
Any help, suggestions, or corrections are greatly appreciated.

 

[RustyRatRod]

My guess would certainly not be above 130 and probably less. The 400 had dismal compression in any form.

 

[Jim Lusk]

It's hard to say because cranking compression is affected by static compression and cam size. Smaller cams and larger static compression will yield higher cranking compression numbers.

 

[PocketAces]

Fuel in the oil, check for a ruptured fuel pump diaphragm. Also make sure the engine is getting up to operating temperature. A missing or stuck open thermostat could keep the engine from getting warm and allow fuel to condense on the cylinder walls.

 

[moper]

From the sound of it, I'd expect something between 100-125psi. You don't say how it runs but I'm assuming "it runs". An engine will run on less than 100 but not very well. I don;t think, if the rings were fuel washed and the oil diluted, that the rings will be of much use either...lol. So get some readings - all plugs out of it, carb wired wide open. Then go back, squirt oil in each cylinder and get new readings. You might want to hook up a battery charger too...

 

[Rumblin_440]

I'm hoping that the oil got diluted from the old fuel pump bc the new one on it now is still outta the box shiny and pumps fuel just fine. I will check on the thermostat tho. The engine does run just barely wants to get out of its own way it seems. I'm gonna go do the compression test now I'll post what I find out. I'm hoping the readings are all close bc I would rather not have to tear this thing down. As for the testing the engine has to be warm and the coil disconnected from the battery correct?

 

[sireland67]

Check your fuel pump pressure.
Clean the plugs, and put fresh plug wires, cap and rotor in it.
What 4bbl did you put on it?
Farm truck for 14 years may need rebuilt, or like my dads just neglected.

 

[Rumblin_440]

I don't have a fuel pressure tester but while I was doing the compression test it was filling up a big gatorade bottle pretty quickly. As for the plugs, wires, cap and rotor they are all new. I put a 650 holley on the truck with a TM6 manifold.

Now the test went better then expected I had an average of 130 with the highest being a 140 on the first cylinder but I went back and tested it again last and it was 135 I think the battery was losing a little juice even with the charger on it. The lowest number I got was 125 that was on 4 of the cylinders. My highest 3 numbers were the first 3 cylinders I tested so again I'm leaning towards the battery getting weak.

So the coil is my next part swap and hopefully that will get the truck woke up. Any other suggestions? I'm also probably gonna replace the battery while I'm at it.

 

[moper]

Excellent results. Do an oil change and remove that TM6 and stick either a stock 4bbbl or a dual plane of any design on it (assuming it's still in the farm truck). That was a HUGE mistake to run that intake. The 2bbl would be better.

 

[Rumblin_440]

Whats your reasoning for that being such a poor choice of intakes?

 

[moper]

That intake is designed for en engine with an optimized cam, headers, and higher rpm operation than what you will typically use a farm truck for. My registered truck never sees the high side of 4000rpm, and mostly runs between idle and 2800. My woods truck never went beyond about 3K and mostly idled around... That is well below where that intake likes to work. it will run, but it will be down on throttle response, economy, and torque from even the factory 2bbl. If you want a 4bbl grab a factory iron deal and a Thermoquad for it.

 

[Rumblin_440]

Well that I did not know but I plan to make the truck streetable therefore need an acceptable exhaust system and the manifolds on it are shot and since replacement ones would be a fortune I had alredy planned on getting headers. Now that you tell me all this thats just more of a reason to slip in a little cam action while the motor is pulled for headers.

 

[william]

My stock 1976 400 was 120 to 125psi

 

[oldkimmer]

......................u can put headers on without pulling the motor............kim,,,,,,,,,,,,

 

[RustyRatRod]

I have a real nice DP4B Edelbrock I'll sell you. I'm gonna use an Edelbrock Torker 383 on mine.

 

[Rumblin_440]

I realize you can put headers on without pulling the engine but I'm banking on about 99% of the manifold studs breaking off. So drilling and tapping will be alot easier with the engine removed.

I appreciate the offer but I'm gonna go ahead and just keep the setup I have.