Need some advice on a truck I just picked up a few weeks ago. That I'm having some issues with. Start out by the truck info....Then whats wrong or what it's doing.

1990 Ford F350 Flat bed/Dump Bed
5.8 with a 5 speed. 73,000 Mile Truck.

Here is my problems....

Trucks untouched...Very well taken care of. Other than someone has disconnected the Smog system and taken off the Converter.

Running down the highway...It will start popping through the Intake/Air box. Mainly does it in high end 4th and all of 5th...Constant popping in 5th gear. And it stays idled up when sitting still unless you hit the pedal real fast. Then it will idle back down..Until you hit the pedal again.....Last night was the first time I really drove the truck since I bought it for my shop.

But in a 40 mile drive...Its used a half tank of gas....Only used the front tank. (Duel tank truck)Considering I could only run it in 4th gear at 65 mph....Even back fired through the exhaust once and just about blew off the muffler

So I'm thinking I should start with timing?? I know it calls for 10 degrees..But with out a Smog System should I keep it there??


Popping through Air Box,Timing and High Idle is what I'm looking to work on first...


Truck does have a new set of wires,Cap/Rotor,MAP sensor also.


Any advice is greatly appreciated in advance!!


Zach

 

Well my truck was popping through the intake also but I have a smog pump on my truck. What I found was my plug wires were bad. I to changed My cap and rotor, sparkplugs, but that didn't fix it, so I put in some autolite proffesional wires and It hasn't popped. Does it do it at like 3000 RPM and up. Mine would, but mines automatic. Now you said theres no smog pump, all the pump does is put air into the exhaust so that it will pass emissions, but this could also mess up your O2 sensor and send bad reading, do you have any codes coming up any check engine light. You could put a pump back in. Also what about your EGR is that working properly. There are many things that can go wrong on these motors, and just because it has low miles doesn,t mean it works correctly. Make sure the right sparkplugs are in it, I put autolite copper 24's in I had put in autolite double platnums in because the previous owner did and it didn't like them. Hope any of this helps......Cody

 

Be sure that #7 and 8 spark plug wire are as far apart as possible. With sequential firing order of two cylinders right next to each other, they are possibly jumping between the two wires. Big problem on these engine's. The air injection system only dumps secondary air downstream of the CAT once its in closed loop. The addtional oxygen helps convert CO into CO2 and NOX into water vapor. Air will be directed upstream into the heads to help build catylist heat to bring it into operating temp. With no CAT I would be suprised if the engine is going into closed loop. The O2 sensor needs to be around 500* to start switching properly, the catylist holds heat in the exhaust to keep the sensor switching. If the exhaust is to cold, the ECU will drop to open loop keeping fuel trim at about 25%. This results in poor fuel economy, and rich running conditions. Wouldn't be suprised if it has code 34 in the KAM. Good luck!

 

The boys have you covered on a possible cause of the backfiring, but pull the codes, check fuel pressure, and check for the fuel trasnfer problem. Codes will tell you if you have any sensor issues, the hanging idle is ofen TPS related.

The fuel gauges in these trucks are notoriously flaky so don't use it as a reference as to how much fuel is used, if both tanks work run it down on one and then switch to the other to get an idea of how far it runs on a tank. Also take note if the mpg is the same on both tanks, it should be but if one tank is dumping fuel to the other it will produce really bad milage while the other will be really good. That also means that if you start with both tanks full then all the fuel the bad tank is trying to push to the other is simply being dumped on the ground as you drive, so be on the lookout for a raw fuel smell right after you park.

 

Dosent a bad fuel pump in one tank result in a fuel transfer situation also? and with a bad pump wouldn't the engine be starving at higher speeds resulting in a backfire?

 

Thanks for the advice so far everyone.

Ok so I changed the plugs and wires again....Found that 3 wires had been melted on the spark plug boot end. Looks like who ever replaced the exhaust gasket left off the heat shields...Causing the boots to melt. So I'm going to try some plug wire heat boots and see if that helps from melting. I adjusted my timing to 10 degrees. Popping is almost cured....Still does it in 4th gear,but no where nearly as bad. Runs great in 5th gear...runs about 80 mph no problem now.

I know I need to scan for codes next...No C.E.L is on,but I know I still need to scan for codes.

I want to work on the Gas mileage problem next...

 

So what would be a cure for this since It no longer has a Cat?? You can smell it burning rich....

Where should I start first is what I'm basically asking

 

well is it worth fixing the truck up or is it worth parting it out. If your going to keep it I would guess you should put a cat on it and a o2 sensor. You should probably put on a smog pump as well and see what happens. bout all i can say.