4.0 OHV Persistent Hard Start. Looking for ideas

[Uncle Gump]

this is what you must mean about holding it wide open to turn off the injectors. I’ll try it

Yes... it's called Clear Flood Mode.

During crank... WOT will stop the injectors from pulsing.

 

[Uncle Gump]

Tip...

If your throttle cable is stretched... it may not achieve the threshold. Ensure you are getting full throttle.

 

[Kirby N.]

I should have checked compression sooner

I started with cylinder #1 when the engine was warm. It read 30lbs. I thought the loaner gauge must be garbage. So I went and bought another gauge.

By that time the engine was cool.

Here is what I got cool:

1- 30 warm with other plugs in. All plugs out 10.

2- cool with all plugs out 15

3- cool with all plugs out 90

4- 50 warm, cool with all plugs out 30

5- cool with all plugs out 65

6- cool with all plugs out 45

I am surprised it even runs.

I added oil to #4 to see if it changed and it went to 40. That could have just been the oil volume.

The plugs all looked pretty lean. #1 looked the best

#3 looked like the rest

 

[Brain75]

Speaking of worn out engines...my 1948 straight 6 had ZERO psi oil pressure (it's a high volume low pressure system so only 50 psi on a perfect motor)... I was shocked, grabbed another gauge, borrowed grandad's gauge, and he grabbed the neighbors too - all zero's... I had added a idiot light with a 1 or 3 psi trip as part of the 6v to 12v conversion and it was NOT lighting 99% of the time.... it ran, it ran fine, I only caught it because when lugging up hills the idiot light would flicker and I started digging to see what was up. "amazed it still ran" is an understatement.

 

[Uncle Gump]

Wow...

That's a rebuild to right?

I have to say...

To run a proper compression test

All plugs out
Fuel disabled
Throttle wide open
Battery charger ON
Crank engine the same amount on all cylinders and be mindful of cranking speed. It should remain constant.

Operating temp is preferred but whatever temp you start should be roughly the same when you finish.

If it were mine... I would rerun it for piece of mind.

 

[Brain75]

I pondered for a moment and came up with something...
A) it really shouldn't run with those numbers, anything less than 90 and it is likely not to run. With 5 out of 6 numbers that bad it really should not be running. As much as I hate to point a finger at the OP and say mistake, I think ya fouled up the procedure and need to re-run the compression test.
B) the 4.0 OHV was super prone to timing chain self destructing, right (or do I have my engines confused) before they self destruct they skip a tooth, is it at all possible he has slipped a tooth and by miracle is still running?
Did it come on all the sudden like one day it was fine, the next it was no bueno?

 

[Kirby N.]

Wot. Screwed that up. Forgot to do that. It’s definitely low on power. But yeah it’s running. Back to the garage. I’ll post up shortly.

 

[Kirby N.]

Ok- made it back to my dad’s in the heated garage for round 2. I am leaving for a trip tomorrow, so I couldn’t bear wondering if I did it right- how would it change.


New test wot and hot engine.

1-10

2- 20

3-100

4- 25

5- 75

6- 50

It is not a wore out engine- that is what is odd. At 38k miles ago, I put in a new remanned motorcraft short block that I had bought off a guy who never used it in a crate. Insides looked spanking new. It had set in a crate for probably 5 years when I got it, it probably set in my possession for 10. It was crated in plastic wrapping soaked in oil. I installed everything new I could possibly think of when I put it back together.

the old engine wasn’t having any problems except it was leaking like a ford. It was wore out from the miles- but it never gave me any issues. It went 314k.

ha. The heads were a bit of a challenge. Because it was a 2000 style block, I had to use 95tm heads to keep it stock compression. I found some loaded nos units on eBay, but when I got them they were 93tm. So i found some 95tms and had a local machine shop go through them and swap the valve hardware.

when i assembled it, it had a noise in the valves. So I took the heads off and took them back to the machine shop. They said they went through everything and it was fine, but that they hand lapped them just to be sure.

I swapped to nos ford lifters from new ones melling ones I bought and installed and the noise went away.

So it still idled odd, but ran ok and I have been driving and tinkering with it.

Any thoughts on what low compression in all cylinders would be? I am wondering if the valves and heads have issues. Might pull them and take them to another machine shop. Sucks.

 

[Brain75]

Any thoughts on what low compression n almost all cylinders would be?

aside from worn out (cam lobes all whittled off, rings shot, etc)
A) valves not adequately opening
wrong length valves installed (not a long enough intake period - gasping for air)
wrong strength springs installed
wrong lifters installed
B) valves opening/closing at wrong time
valve timing off (i.e. slipped chain)

Those were the ones that came to mind right away...a quick google gave me this.... which adds all the worn items back and a few others I didn't think of right away.

8 Reasons Your Car's Engine Compression Is Low

Low compression is often a sign of an old and worn car engine, but it could happen for other reasons also. Here're the common ones

mechanicbase.com

 

[Kirby N.]

The common timing chain issues is the sohc 4.0 I think you are referring to.

 

[Kirby N.]

looking to see if it starts easier (normal like).

I tried that and it didn’t start at all if I held it wide open. Need to pedal it.

 

[Brain75]

well based off the last thing I googled up, I would try the quickest/easiest/least destructive tests and work up to the more invasive (i.e. take the oil cap off and look for smoke/steam/pressurization etc - blown headgasket, before pulling a valve cover- costs a new gasket, before pulling a head - lots of lots of work)...

double check your coolant for signs of contamination from a headgasket issue.
maybe do an oil change and check the oil for contamination.

run over the complete vacuum system for a leak is on the list for all your issues except low compression... low compression tosses that out as a primary issue, might have it, but it would be secondary.

 

[Brain75]

probably sneak a leakdown test if you think it is warranted, because while it is time consuming it is cheap...

 

[Brain75]

from the conditions of your spark plugs, I completely rule out #7 in my own mind if it was me (fuel dump washed out all lube "washed cylinder walls")

 

[gaz]

@Kirby N.
NOT STOCK COMPRESSION RATIO
• Your rebuild has 1st gen OHV 4.0l small dish pistons
• with 95 heads, which are the fast burn combustion chamber (smaller combustion chamber).

The combination if these two components result in approximately 10.2:1 CR. Depending on how much was milled off those heads you are higher no matter what, just a question of how much was milled. Either way you may need try a tank of premium fuel.

That 93 computer can be either a Sequential Fuel Injection (California with EGR) or MPFI (Federal, non EGR). If it's the EGR PCM, that isn't helping.

Your compression test numbers are wack. How many miles have you put in this rebuild?

Since your fuel pressure is dropping, a prudent move is to install a new gas cap for the filler hose, could be leaking, often overlooked.