Hey gang,

I have a 93 F150 with the 5.0, and I can't get it to run right! I did an engine swap this past fall because the engine was getting tired and had a really bad surge at idle. Bad enough that it would stall the engine.

I bought a truck that was the same year, with a freshly rebuilt engine to swap in. I replaced all temp sensors, tps, iac, ecu, pretty much everything required to run the engine, including the engine its self and I still have the exact same problem! any ideas? I can give more info if needed.

 

Have you checked fuel pressure? Fuel regulator? Does it run okay beside not idling?

 

Have you checked the throttle body blades? Any daylight where they close isn't good. Worn throttle body shaft, incorrect fuel pressure are some key points. Also bad PCV valve could allow to much exhaust gases back into the combustion. A malfunctioning O2 or its circuit, interference with the TPS, incorrect timing are just some of the ideas.

 

First, before the engine swap, did the old engine run well.
If so, then its something you did while swapping the new one in.

Tell us what you've done so far. Have you checked codes.
Idle air valve could be sticking, map may have not been hooked up.
O2 sensor or even the evap purge solenoid could be stuck.

Give us a list of what you e done, and we will go from there.

 

Alright, lets see if I can respond to all of you....

Freightrain: I had my uncle do most of the work during the swap. I was too busy, and he is retired, I took advantage lol. I think he checked the fuel pressure, and it was fine. The regulator was in good working order, and when going down the road, with my foot in the pedal, it seems to run fine.

Timbersteel: I have not taken that close of a look at the throttle body. It is the original, and I assume unmolested from the factory. I am however adding that to the list of things to look at. Already addressed the fuel pressure, but I'll check it again and report back. PCV system as been eliminated. I never liked that system, and when I get this deep into a project, I just rout it to a catch can with a filter for air movement. So PCV system is eliminated. Along with the air pump. That has been deleted and plugged off. O2 sensor is brand new, TPS reads fine when back probing, and I'll get into the timing further down.

Untamnd: Before the engine swap it was doing the exact same thing. The main reason I did the swap. It didn't run right. The engine seemed tired, had a bad idle surge, and when I decided it was time to do something, it was because I was driving to work one day, and it stalled out on the road. I could start it, but hardly keep it running. I spent 20 minutes in a parking lot trying to turn around and get it back home. The new engine runs better, but still has a lot of the old issues I was dealing with.

As far as codes go, they have been EGR related, because I eliminated that system. I have a sensor plugged into the EGR position plug that gives a constantly closed voltage from "old ford fuel injection". After the swap, the only thing that wasn't changed was the IAC and ECU. I was hoping the a new IAC and ECU might do the trick. That's why I'm asking now because I just replaced those. When I swpeed the engine, I replaced all the sensors I could find, water temp, air temp, O2, etc. It's full of new sensors, and still not running right.

It seems like a surge idle can be cured by going to mass air, but with the whole system being brand new, it should run like it did out of the factory! As far as setting timing, the engine I have has had some work done to it. A 4x4 cam for a 351 has been installed before I had it, some head work done, and I think that's about it. We originally set the timing to what the manual called for, can't remember for sure, but 12* before TCD with SPOUT out sounds right. Then we started setting it to the vacuum at idle. Timing should be close. Seemed like the best vacuum we got was 14psi. I dont know if thats because of the cam, or maybe a vacuum leak yet in the system.

This is what I'm thinking so far...

Check fuel pressure, inspect throttle body, put a vacuum pump on the system and try to locate any leaks, and trace any ground wires and inspect/clean those connections. I welcome any other ideas, and I'll keep updating as I go.

Thanks for the help thus far, and if you have any more questions/thoughts/comments, please reply. I need all the ideas I can get now!

 

Yeah I would definitely check the closing area around the TB blades. If there is any daylight coming through where they close, it'll give you a terrible idle surge. That was a everyday problem before I swapped it with a BBK TB. What is your TPS voltage when blades are closed? With a tach hooked up, what is your RPM with IAC connector disconnected? These are just some other ideas.

 

My buddy had a truck that would do the same thing, he sprayed a little throttle body cleaner on the plate and it help greatly.

 

Sorry it took a little while to respond, but this cold weather snap has driven my ambition away lol.

I did get the chance to take the throttle body off yesterday, and noticed daylight all the way around the blades. Looks like I have found at least on problem!

Does anyone have any good sources for throttle bodies? Rock Auto doesn't seem to carry them, and the BBK looks like a nice option, but pricey. And buying a used one off ebay might have the same problems mine has. Am I stuck with the BBK one as of now, or does anyone know of a source for good OEM replacements?

 

I would check your local junkyards or might try an online parts finder/inventory from junk yards across the country.

 

I purchased a used BBK TB for nearly $75-85 less than new. It was money well spent though. It eliminated a major headache in the long list of crappy problems I had to deal with when I bought the worn out truck.

 

Bringing this thread back, got some new info...

Still not running quite right. I did end up getting a BBK TB brand new and installing it. When it was first put on, the truck would not idle at all. I had to open the blades a bit to let enough air in to run on its own. After that, I still had idle surge, and was running pretty much the same as it did. Once the weather broke, and it got a little warmer around here, I fired it up again, and it did run better, until putting it in gear, then the surge came right back. Take it out of gear (put in park or neutral), it would kind of clear up.

I keep thinking vacuum issues, and it finally dawned on me. There were several vacuum leaks before doing the engine swap, and the engine that is in it now has a cam that doesn't create much vacuum (highest I ever got was 14psi). So follow me here...

MAP sensor has never had a good, full vacuum reading ever sense I've had the truck. I disconnected the vacuum line, plugged it, and put a hand held pump to the sensor and played around with it while putting into gear, idling, etc, and I could get it to run much better than it ever has.

So is there a way to either re-calibrate the MAP (it throws a frequency, not volts to the ECU), or possibly a vacuum pump that would be a simple bolt on?

 

To me it sounds like you have a cam in there that is NOT speed density compatible. Really your only good and reliable options (if the cam is throwing the SD set up for a loop) are mass air conversion or a dyno tune with your speed density set up. My vote is for a mass air conversion since it can adapt to changes you make further down the road. A dyno tune with an SD system has to be retuned any time you make alterations to the set up. Oh and you could always put a factory cam back in.