I have a 1997 Mustang GT with a '00 Ford Lightning engine. I bought the car with the engine already installed and the wiring finished. The engine has about 5k miles and is backed by a T45 manual trans. I had to do a few minor things to make it drivable and had it tuned with an SCT chip for 91 octane last year. The car was mostly stock aside from an exhaust and 4 lb. lower pulley. The cars intercooler was empty because the H/E was not installed yet. Non-intercooled it made 375hp/475ft. lbs. at the wheels with very high intake temps. After the tune I installed an '03 Cobra H/E and pump, huge intercooler reservoir and an OEM 90mm mass air sensor. I did not drive the car much before installing the heat exchanger. It felt plenty fast but the s/c would heat soak quickly. After installing the new parts, the car seems to run about the same until it warms to operating temp, then it feels much slower. Full boost goes from about 11 lbs. to 4-5 lbs. and the car feels strained, like power is being restricted.

I have several theories but would like some opinions/suggestions. The engine has had a "boost bypass" mod done, but I'm not 100% sure it is correct. I don't think this is the culprit because it boosted fine before the new parts.

I am not sure if adding the H/E and MAF affected it. I would think the car would run better and I contacted the shop that tuned it and they said the H/E would only make the car faster due to lower intake temps and the larger MAF might affect the idle slightly, but it should not cause boost to drop suddenly and make the car lose power. I put the 80mm MAF back on the car with no change. I would like to have the car retuned, but don't want to throw $400 away to have the car still run poorly due to something else.

The car is not throwing any check engine codes or overheating. If you have any ideas or suggestions, please throw them out there.

 

Start with the basics- fuel filter, plugs, check battery as voltage issues can cause odd problems, you mentioned that you pulled the MAF an upgraded-that needs a tune change I believe, start there and report back.

 

If I'm reading your post correctly, your main issue is boost loss.

If so, then I would check for belt slip (any dust on the pulleys or SC snout). Then I would make sure that the boost bypass valve (the valve itself) is adjusted properly.

 

There was a little dust around the pullies, but I washed the engine a while ago and haven't noticed any since. The belt is in good shape and appears pretty tight. I checked the boost bypass valve and it is opening and shutting correctly according to what I've read. I pulled the plugs and they looked okay, maybe a little on the rich side but not fouled. When at WOT, the supercharger whines like it used to, progressively louder as the RPMs rise, so that leads me away from the belt slip possiblility as well. Also, the intercooler/heat exchanger fluid is pumping fine and never gets hot.

Is it possible the ECU is pulling timing or reducing boost? I thought the 255lph single pump might be the culprit, but the tuner said the car had plenty of fuel when he tuned it.

 

Many of the usual hardware issues won't cause loss of boost.

What type of filter/induction system do you have. Is there a chance that a rubber intake tube is collapsing once it gets warm and soft? Is the filter clean?

If a) you're not restricted on the intake side of the blower and b) the boost bypass is operating properly, you should be making good boost.

 

The intake consists of the stock lightning intake boot, the MAF and a large K&N filter on the MAF. The filter sits behind the drivers side headlight. The boost bypass is where I am kind of confused at. I checked several writeups on it and believe I have it right, but unfortunately my vacuum hoses are routed a little different and don't seem to be the same colors as the ones in the writeups. After installing the new parts, I did change how the previous owner had the vacuum lines routed because they were way different than the write ups people did. If I manually open the bypass valve by hand, I can hear the s/c get louder. The valve also opens up if the engine is revved. I will try to get some detailed photos of the bypass set up, perhaps it is incorrect. Thanks for the help so far.

 

If the bypass valve opens when rev'd, then you've got the hoses connected wrong on the bypass actuator - it's supposed to be open when idling or under light load and closed when rev'd or WOT. Test and put the hose with vacuum at idle on the top port of the actuator - you can leave the bottom one open or go ahead and connect it to the small nipple on the bottom of the intake tube.

Bird