cmoore2468

Does anyone have any ideas what may be going on with this truck? The O2 sensor has been changed,new rotor cap, new timing belt, and plugs. I think the vacuum hoses are okay? Any help will be appreciated! Thanks!

Jasper 83

How is the power? has it lost some? What about fuel mileage?

cmoore2468

To be honest I am not sure how the power is or the fuel milage. I just bought the truck and I have been driving a 7.3 diesel for yrs. the last toy I had was a 1989 22r. I think its getting about 15 mpg with a 4" lift and 33's underneath it which I dont think is to bad. I can feel the miss when I am driving it almost feels like a lull and surge.

Jasper 83

We just put two heads on a buddy of mines 3 liter. He had a dead cylinder cuz one of the exhaust valve seats was gone. Id try doin a tune up first and maybe a compression test while u got the plugs out then go from there. I don't know much about the 3.0 other than it is a PITA to work on. It has become my new nemesis haha

vasinvictor

iTrader: (3)

Check compression and report back.

CajunKenny

Also, re-check timing.

Then move on to the fuel system.

cmoore2468

The guy I bought the truck from said that he did a compression check and it all checked out. Maybe I shouldnt take his word and have it checked again. Can you check by removing spark plug wire individually?

vasinvictor

iTrader: (3)

You'll get best result by removing all the spark plugs before testing. Also one other thing to consider, does the "lull and surge" happen when the A/C kicks in and out? I know that I can feel when my A/C cycles. It'd be worse if your refridgerant was low and your compressor was cycling more quickly. What RPM does your rig idle at? Do you feel the miss at idle?

CajunKenny

It's easier on your starter and battery to remove all spark plugs for the compression test. Also, pull the EFI Fuse.

Try to turn the engine over the same amount for each cylinder. 5-6 revolutions will be sufficient.

A compression tester can be cheaply had at your local Harbor Freight store.

SnowDrive215

Check compression, plug gap, timing and fuel system.

bone collector

mine did something similar put the battery cables were working themselves loose. check there too

cmoore2468

I am going to purchase a compression tester and will let everyone know how that comes out. My mechanic said to leave it on there for about 3-4 minutes and it should have 135 pound of pressure and if its lower than 90 its bad. Is that correct?

CajunKenny

I'm going to hope that your mechanic means to leave the gauge on each pressurized cylinder for 3-4 minutes and does NOT mean to crank for 3-4 minutes.

I don't have the exact minimum cylinder pressure specs with me so someone else will have to chime in there; but, what you're really hoping to NOT find is big difference in pressures.

Example: Here are Toyota's specs for my Supra.

156 psi and above = Good
128 psi and below = Bad
Max Difference Between Each Cylinder = 14 psi

That said, if an engine has low compression; but, somewhat close compression across all cylinders, it will still run pretty well.

TNRabbit

Leaving the tester on for that amount of time is called a leak-down test. That will tell you if you have overly worn piston rings or a valve that's not sealing completely.

cmoore2468

I have read that on a 94 p/u the diadnostic port is on the left hand side near the fuse panel. My truck does not have a port there, could it be that I dont have one? I have a 94 x cab 3.0 4wd. The check engine light is on along with the rough idle and lulls and surges. I plan on getting the compression checked this weekend if possible.

Thanks!

TNRabbit

The gray box next to the fuse panel above is the OBD1 plugin.

Also, check this video & see if this is your issue:

cmoore2468

Man, thanks for the info! I have been thinking it was the EGR valve but did not know how to check it. In the haynes manual it says that sometimes thos things wont close and can make it idle bad. I am going to check that this evening and let you know if that is the problem! Once again thank you!

CajunKenny

I politely offer a correction. A "Leak Down Test" is performed differently and with different equipment.

TNRabbit

I understand that but a leak-down test is what was being described....

cmoore2468

Cant a leak down test be down with a compression tester?