got a 94 Ranger, 2 wheel drive, 4.0 w/ about 160,000 mls on it. It runs pretty good but has bad spark knock when when I step hard on the gas.

Just got this truck for work. normally I would think timing but this thing is electronic and I'm not familiar with that so not sure what to do.

What do you all think?

 

Welcome to FTE!

The three most common reasons for engine knock on the 4.0 (in no particular order) are:

*dirty MAF
*loose lower intake bolts
*engine needs to be decarboned.

All are easy and cheap to fix if you do the DIY route. There are many posts on the issue. In the sticky titled tech info, there is info on decarboning the engine (Ford issued a TSB on this) and I think cleaning the MAF is in there too. And as always, look for any vac leaks. Lean mixture = high combustion chamber temps = engine knock. And finally, using higher octane gas and/or removing the jumper to retard the timing are not the fix; they just mask the problem. Besides, retarding the timing costs you gas mileage and performance. Hardly a fix .

 

Thanks for the info billy. I'm new to this forum and still learning my way around but the info in the sticky was very helpful.

 

wannaknow: All of the items that Bill mentioned are and can be causes of your spark knock. There is one further item to check and that is the port that is under your EGR valve. These have been known to carbon up restricting the exhaust gas flow.

The exhaust gases are actually used to "cool" the combustion temperature thus reducing the chance of spark knock.

Clean the MAF first and a wrench on the lower intake manifold bolts to ensure that they are tight is the best first step.

Keep us posted.

Russ

 

Thanks Russ, I have not done anthing yet--still reading up and appreciate the info.

I tend to think that it's a carbon issue. When I first got the truck I changed the plugs and 3 of them had the electrodes burnt right off. I could hardly believe it because the truck was running quite well.

I see that the intakes on these trucks have a tendency to loosen up so I will be checking that and will be flushing the carbon out as suggested. Just need some spare time and good weather. I stopped by Ford and they didn't have the PM-3 so I'll have to go some where else down the road.

Do you know of any sites that have good diagrams for free?

 

Just a FYI, only 94 4.0 Rangers sold in Cal had an EGR system.

What diagrams to you need? Autozone.com has lots of good repair info in there. If not, let me know what you are looking for. Torque values and sequence on that lower intake by chance? To torque those bolts, you will need a couple of swivels, extensions, and a torque wrench.

 

This weekend I cleaned the maf sensor on my 94 b4000, as I was experiencing this issue. At 90,000 miles I could see the dirt build up on the wires. Put it back together and test drove.... PROBLEM SOLVED!! Thanks CowboyBilly. You and this site are a wealth of info.

 

Glad to hear the problem is solved . Lots of great people here on FTE; just about anything that a person could ever need help/advice with can be resolved here. I think of FTE members as family .

 

Thanks again for your help, much appreciated.

Yes, the torque values and sequence would help and, I hate to reveal my ignorance but, where is the MAF sensor located? I've never owned anything without a carburator and distibutor cap so it's a learn as I go type of thing. I hate taking anything to a mechanic around here--they seem to break more than they fix. Just figure it out and do it myself.

I did the MP-3 as suggested but didn't seem to help. So I'm gonna torque the intake and clean the MAF next.

 

I found where the MAF sensor is located in the sticky and will folow the instructs I found there.

A new problem to mention--A couple days ago I was working in a field and got stuck in the mud. After I got pulled out the brake light and ABS light came on. I took it to the car wash and cleaned real good but the lights are still on.

What do you think? The brakes are working fine.

 

Here is the torque sequence on the lower intake bolts : http://home.comcast.net/~cbb9m/94_4....e_sequence.jpg

Torque the fasteners to 24 ft-lbs. I would suggest doing this in three steps; 1, 16, then 24 ft-lbs.

On the brakes, the steady light on indicates you hve a fault in the RABS system. It's time to pull codes. In the sticky at the top of this forum is info on how to pull the codes. This should help.

 

thanks much for the info CowboyBilly.

 

I bet you damaged the wire to the VSS thats mounted in the top of the rear.

 

Thanks for the help Ken, I'll check it out.

Where is that located and what does VSS stand for?

 

VSS = vehicle speed sensor. It's located on the top of the "pumpkin" on the rear end. There will be a wiring harness leading to it.