Storyline: I'm looking at a car to purchase, and the dealer didn't do the compression check correctly.

Facts: From all the other dealers, what I read up, and OEM specs, Nominal should be 142 and Max is 200

Facts: Compression with OPEN throttle, and Pull the Fuel Pump Relay (Is how I needed to be done) and with this done, the others cars in comparisions are pulling in 190-195-200PSI.

Facts: This dealer did warm the car, OPEN Throttle, but "forgot" to pull the Fuel Pump Relay.

#'s came out to 160 across the board. (according to the tech) and leak down < 5%.

Facts: All the other same vehicles, with proper open throttle and fuel pump relay pulled, are showing 190-200PSI.


Question: Can "forgetting" to pull the fuel pump relay LOWER the PSI by 30-40 PSI?!


My thoughts are 160 across and <5% is a healthy motor, but my other half says, even with the fuel pump relay not pulled, it can't give a false reading of 30-40 points lower can it?


Thanks S2ki,

BC

 

something is not right there, I would guess there is something wrong with their compression tester but I also think its strange that the numbers were consistent between every cylinder... If I were you I would go to autozone or a similar store and get your own tester for around 20 bucks then test the car on that tester.... If the numbers come up the same then my guess would be someone lowered the compression on that car to go forced induction, but even if you lower the compression I don't think it should be that low but I could be mistaken.

And to answer ur question, not pulling ur fuel pump fuse will not lower the test results by that much to my knowledge I don't think it effects the test results at all

 

That's my understanding also. The only problem is the car is 400 miles away from me, so I only have a dealership to trust.

I do know gauges vary from one to another, but not by 30-40 PSI right?

 

Letting the fuel fuse in will not lower the numbers. Worst case you get fuel in the cylinders and then you would raise the #s, due to fuel taking up space and maybe even sealing the rings some.

I guess the reason why people like to remove the EFI fuse is more so not to wash the cylinders with fuel.

J

 

that dealer needs to be shot...

reasons why the fuel relay should be removed:
1) if fuel is injected and 3 of the 4 spark plugs are still in the car, the engine might start running during the compression test. IMO, this is a safety concern. you don't want the car to start up accidentally during the compression test. there'll also be lots of unburnt fuel going into the catalytic converter (this is bad).
2) if fuel is injected and spark plugs were removed, all the unburnt fuel is going into the exhaust. when you start up the car, the catalytic converter will burn all that fuel. don't be surprised if your catalytic converter will need replacement shortly.

btw, your compression results are very low. most people on this forum report that theirs is around 220psi (honda spec is around 160-228psi, the dealer is lying about 142psi being nominal). my car did 240 -245psi when it had 80,000miles. leakage on my engine was between 1-1.5%. i'd say 160psi is too low even though it's still within honda's spec. if you haven't purchased the car yet, i'd look for another car...

 

I do:

-Car hot
-remove all plugs
-unplug 4 injector clips
-WOT
-crank each time 6-9 times

I usually get numbers around 220-245.

IMO, fuel spraying into the cylinder will lower the number, as it will dilute the oil on the rings.

-in any case, fuel delivered into the cyl and not burning is just not good practice.