When you have a chance, put a vacuum gauge on it while it's idling. For speed density to operate properly, it'll need to be at least 16in/hg or higher. A lower reading will cause the motor to surge and run rich at a lower engine load.

 

I'll get a reading this afternoon and let you know what I come up with. Thanks

 

Did the vacuum test. 15in/hg

Doesn't seem to surge, but definitely smells and acts like it's running rich at low rpms and under load at low rpms.

 

Thats a little low , but it should still should have good power at WOT from a standing stop , the low vac will cause idling problems , sounds like it could be the timing , i would check the base timing again with the spout out , then plug it back in and see if the computer advances the timing , you could also have a slipped balencer or a bad light , you could also set the timing by ear , advance the timing and with the vacuum gauge hooked up and see what it does , its worth a shot....by the way what is the gearing and tire size on your truck....

 

I've tried the timing at 10, 12 and 13. No significant change, but it is a little better at 13 than 10 for sure.

I had someone help me check the balancer. He held a screw driver in the #1 cylinder and told me as soon as the piston dropped away from TDC in both directions. I put a mark on the balancer on both sides. TDC was it was exactly in the center of the 2 marks (the marks were at 10 BTDC and 10 ATDC. I also checked TDC on the timing marker with the truck off. I turned TDC to the timing marker on the timing chain cover and checked the rotor to make sure it was at the number one position. All was good. BTY, I am using the harmonic balancer from the mustang and not the original truck motor.

New timing light, but I did check it to see if it matched what the light showed by rotating the crank so that the 10 degree mark on the balancer matched up with the timing mark, then checked so see if the rotor was at #1. All was good here too.

I settled at 13 because it ran and sounded better there than any where else.

I haven't advanced the timing with the vacuum gauge hooked up to see what it does. My daughter took the truck on a date! I guess we know what's most important here now don't we: (I'll have to do it in the morning)

Tires are 285/70R 17 and 4.10 gears.

Could the 15in/hg make it run this bad?

 

Try the timing and make sure its advancing with the spout in , could just be the cam , i have went over on cams with SD , the main problem was idle and stalling coming down to idle , but ran fine at wide open throttle even on the low end ....

 

Okay, I finally got the chance to check the timing. Here are the results;

SPOUT OUT - 14in/hg 12 degrees BTDC
SPOUT IN - 15in/hg 14 degrees BTDC

So it did advance 2 degrees.
Tried it at 10 degrees BTDC and got basically the same results. (1in/hg less vacuum and 2 degrees advance with the spout back in)

It idles good and has never stalled coming down to idle.

Just NO power on the low end. I think a bicycle could kick my butt in a 100 yard dash.

Thoughts?

 

I don't think you're getting enough computer timing advance, it should jump 10 deg or more when you plug the spout back in and you should see 32-35deg total when reving a little above idle. Are you using the original truck distributor? Do you have a spare TFI module to try? It has to be the same color as was originally on your truck.

 

Yes, I'm using the original truck dist.

I don't have an extra TFI module but I may be able to borrow one off another truck for a test. I thought that TFI modules where either good or bad and either work or don't. I didn't think there were any symptoms of one going bad.

I'll see if I can get one and try it. It should be just a plug and play test shouldn't it?

 

Most auto parts stores can test the TFI module for free.

 

Wow. That's very helpful. I'm having a hard time finding a loner. The one I thought would work is different. I'll take it in to get it checked ASAP!

 

Okay, that wasn't as easy as I thought it would be. I tried all 5 stores in town and no luck. I finally started calling part stores and repair shops. It took a while but I found one about an hour away in a neighboring town that could do it.

Anyway, We tested it three times - all three were good.

The original problem with the truck was a piston had slapped a valve. I went to my neighbor who builds racing motors and asked him if he could do a valve job on it. He said he had a motor out of a 94 Mustang Cobra GT in the back that he would sell me for the same price as doing the heads. So I put the Mustang HO motor in.

It's NEVER run right since the install. Nobody could figure out what the problem was. It had some leak down and low compression so I took it back out and rebuilt the entire thing.

I put it back in and its STILL never run right.

My gut tells me I need to focus on what changed from the old truck motor to the new stang motor. Something related to compatibility issues. The truck motor never ran like this before it came out and and the mustang ran great before they took the motor out.

The only compatibility issue I can think of is the HO cam (whichever one it is) and the SD system. Oh BTW, I noticed I said in the beginning that it was out of a 93 stang, I was a 94. I don't know if that makes any difference or not.

Are there any other compatibility issues I'm missing here? This swap has to have been done a thousand times.

OMG, the other day I pulled up to a "sloped" residential curb when I was pulling into a friends driveway - from a dead stop the truck couldn't pull itself up over the curb. I had to take a run at it. That's how gutless it is on the low end.

 

Yeah that ain't right, but lets go back to the ignition system again. Can you confirm how much advance the computer is applying with the spout plug installed? If it's only adding a couple degrees then that's no good the motor won't make any low rpm torque, and if it's not a TFI or PIP module problem it could be the computer itself. I'd suggest swapping in another distributor to test the PIP module, that part is inside the distributor and changing it involves completely dismantling the distributor so it's much easier to simply plug in another distributor. A local wrecking yard is a good place to get a test part and the Ford electronic modules are higher quality than aftermarket parts so I wouldn't hesitate to use these as permanent replacements either if it fixes your problem. The other thing you should do is pull the computer codes to see if anything is flagged, this can be done without any special tools but an inexpensive code reader like the Equus 3145 takes all the guess work out of it.

 

What do you think about upgrading the ignition system, (dist., wires, coil, cap, TFI, etc.) with a performance upgrade? Waste of money?

Is the truck dist. the same as the stang? I have the truck dist. in now. Should I be looking for a dist. out of a truck motor or the 94 HO motor? Or does it matter?

 

Okay, I thought I should update this thread with the answer. YES I do need a MAF conversion. It seems that the cam in the Mustang Cobra GT is not compatible with an SD motor. After doing lots of research I decided that there was really no downside to doing the conversion other than the degree of difficulty. I figured it would be a bonus either way even if it didn’t fix the lack power on the low end. WOW - What a difference! It’s like night and day. MUCH more power, MUCH more responsive and no lugging/chugging on the low end. Runs Perfect.

I went to the junk yard and found a 96 f250 with a 5.8 and an E4OD. I took EVERYTHING from the ECM forward. (ECM, Main harness, engine harness, transmission harness, air ducts, filter, MAF sensor, and the tee in the heater hose to get rid of that stupid hose that runs from the radiator by the filler cap to the throttle body). The total bill at the JY was a whopping $75.00! I did end up putting on a KN filter system which helped a lot, but I would never spend $200 for something I could build for $25.00 or $30.00 again!

The conversion was really pretty simple after I understood what went where. (About 4 or 5 hours of research for every hour under the hood)

I suppose it’s possible that the problem was something else other than the MAF conversion and it got fixed in the modification, but either way it runs great now.

The only remaining issue is the CEL comes on after about 10 minutes of driving. It stays on steady, doesn’t blink any codes, and has NO affect on how the truck runs. If I shut the truck off and restart it the CEL is out until about 10 minutes of driving again. Always goes off after the key has been turned off and always comes on after about 10 minutes of driving and stays on until I shut the truck off again. No codes on KOEO test and when I do KOER I can’t pull the codes because the code reader reads the codes before the CEL comes back on. (It shows no codes - pass 111). Hummm. More research I guess.

Thanks to everyone for their help.

BTY I used this site extensively to do my research when I was doing my conversion. Lots to sort through but it’s there if you look hard enough.