When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello all
I have a beautiful like- new '98 5.4l very clean and well maintained.
It has a strong engine that has been bucking under pressure. It idles fine and runs great when its cold but once it warms up and you accelerate it bogs down every time.
I have owned this truck about 3 years and always used only Motorcraft parts & plugs. I have replaced cops and plugs used dielectric grease on the boots, cleaned my K&N filter, and had a shop install a new fuel pump and filter (much easier to do on a lift). It still bucks and the mechanic (nice guy) suggested the cats were clogged. I removed, gutted, and reinstalled them just to eliminate this as a possibility, and I DID gain quite a bit of power when the truck is running ok - but it did not solve the problem.
I've rechecked for vacuum leaks, cleaned the MAF, and everything on the truck checks & tests out fine (no codes).
I have a Jeep I'm using as a daily driver but I need this truck to pull my work trailer, but I cant afford to keep throwing money at this truck. I do have a innova 3040rs obd2 reader but not a ton of experience with it.
I realize there are many threads on this subject (Ive stayed up nights reading and applying the suggestions) but nothing seems to help.
Does anyone have experience with this or similiar situation and found a fix? Or
know a legitimate way I could test the cops to know if maybe I bought a bad one? I have a tester light that attaches and its lighting up on every one- but that doesnt really tell me if they're working PROPERLY.
Thank you for the replies & suggestions. Out of curiosity I bought an additional COP and tried it in each port (remove old cop, insert new and start motor) to see if I detected any change and I sure did! One of the brand new Motorcraft cops was faulty and when I got to that one the motor leveled right out!
After driving the truck a bit the sluggish acceleration returned!
My next attempt was replacing the IAC and BAM! The truck was suddenly at nearly FULL POWER when accelerating, but I can still feel the misfire 😐
It still idles great but if you pay close attention you can slightly feel the miss at idle.
when accelerating I can feel it intermittently falling off, and the rpms drop about 2 rpms each time I feel it.
I'm a single dad and this is the truck I use to pull my work trailer. Please help!
So far Ive;
Paid a shop to replace the Motorcraft fuel pump & filter ($865) -much easier on a lift
Replaced all Motorcraft coils and plugs ($389)
Replaced the Motorcraft IAC ($108)
Thoroughly cleaned & re-oiled the K&N filter ($15 for the kit)
(admittedly it's an old K&N, but I replaced it with a new one from another truck with no change.)
Thorougly cleaned the intake with B12 chemtool
Replaced several vacuum hoses and others that seemed cracked/dryrotted.
Cleaned out the cats (bored them out)
cleaned the MAF sensor (and temporarily replaced with a new one, with no change)
I also purchased an Innova 3040rs with 'FixAssist'- To be honest I'm a novice with this tool. I'm not even sure how to access mode 6(?) but I'll try to attach photos with useful Info(?)
I'd do a compression test. Throw a couple bottles of Techron in the gas to clean the injectors.
Originally Posted by Roadie
Fuel pressure?
Fuel pressure should be 28 to 40 psi, should rise at least 5 psi when vacuum removed from pressure regulator on the fuel rail. Parts stores should have a pressure gauge in their loaner tools.
Now a local mechanic is telling me the timing chain is probably bad(?)
Would an engine idle like new and only misfire when warmed up because of a bad timing chain?
still can't hold 70mph
Fuel pressure is good new pump and filter, New cops, New plugs, new iac, new maf sensor, no codes, o2 sensors working properly- can anyone solve this mystery?
