Well I'm still having boost problems....

Heres what I've changed:
DIS
Coil Pack
Plugs x2
Wires
Cam Sensor
Fuel Filter

And here's what it's doing.....
Car runs perfect while in vac. Once I cross into any sort of boost the car feels like it's bogging down, and weighs tons. It's not throwing any codes either. I've changed the plugs twice, first time some crappy plugs were put in, the second time I went with some splitfire plugs. They're not platinum plugs tho, do the plat's really make that big of a difference?

Either way does anyone know where I should start next???

Split fire won't work worth a crap in the SC. Go back to double platinum or iridium. Those are about the only plugs that work worth a crap in these cars. I've got the iridiums in my '89 and have not troubles at all.

Also, install tbird88's intercooler gaskets. I remember posting with you a while back with the same troubles. You've spent a good amount of $$ replacing those parts. Try the ~$20~ for the gasket and the little time for the install. Start with the simple stuff first because generally speaking, those are where the problems are. I fought the same problem you are now for over a year. Couldn't track it down. Did a tune up to include the gaskets and have had no problems since.

Either way does anyone know where I should start next???

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I think you don't have enough fuel pressure. It could be very simple, like the vacuum/boost refrence hose going to the fuel pressure regulator isn't attached or is leaking. The regulator itself could be bad, or the pump isn't providing enough flow under high pressure.

The easiest way to determine if it's fuel is buy a test gauge at autozone and see if your pressure is increasing pound for pound with boost. For example, if you showing 10 pounds of boost you should be getting 50 pounds of fuel pressure. Static pressure (with vacuum hose off) should be 39-40 pounds. With hose attached pressure will be lower than static pressure depending on how much vacuum your pulling, but most will show 33-37 psi.

David

Dave,
I was wanting you to clarify something for myself and SLP007. If he was not having enough fuel pressure wouldn't that cause a lean condition? And (I'm assuming that SLP007's SC still has the stock computer, and no tuner type mod) the stock air/fuel ratio's are very conservative. In order to make more power off of a stock SC, you lean out the fuel ratio a little. That makes more power, right? And if it gets lean enough to produce adverse driving performace, wouldn't you already have a problem with detonation?

I am under the assumtion that a rich condition will lead to the "bog" feel of the car. My personal experience has confirmed this thought as well. I re-sealed my IC tubes and I no longer had the bogging down and missfires under boost. Please shed a little more light as to your thought pattern for us who are not as car wise.

Everybody has given good advice so far. I'll throw some of my own in here.


I would recommend Motorcraft double platinum plugs, and I even run .052 gap. I would also recommend Motorcraft 8MM factory wires. They work for me with a 10% pulley and 14 lbs boost. Even if the splitfires are junk you would think they could handle 5 lbs boost. If the car doesn't pull at that boost you might want to check timing. No timing advance gives you the symptoms you describe. Because the harmonic balancers fail so often on a SC you can't just check with a timing light. Trust me, my balancer was broke and had slipped at least 12 degrees on the crank. The car had no codes and checked 10 degrees BTDC when checked with a timing light. To check timing you need to use a TDC tool or wooden dowel rod to tell when the 1# piston is at TDC. Now check the balancer to make sure it lines up to TDC. If the balancer breaks it can slip on the crank and still show perfect with a timing light. This is due to the timing being derived from crank sensor ring on the back of the balancer, but if the balancer has slipped then it wont be really where it should be.

Once you have the cold timing known good, then move on to a timing light and check base timing remember to unplug the spout jumper first. ALso put a external vacuum guage on the car. I always plug right where the factory guage plugs. Let us know your vacuum reading at hot idle. I get 21 inches on my 89 SC in park and 18 inches in drive. The factory guage on mine reads about a needle width below the In Hg marked on the guage. Thus it doesn't read more than 19 inches on the factory guage so it's not that accurate.

Good luck

What shockwave said....

I also have 20 in in park and 18 when it is in drive..Sometimes after boost I can bust a 23... If I have bad gas my car will sputter and bog down when I go into boost....

Dave, I was wanting you to clarify something for myself and SLP007. If he was not having enough fuel pressure wouldn't that cause a lean condition? And (I'm assuming that SLP007's SC still has the stock computer, and no tuner type mod) the stock air/fuel ratio's are very conservative. In order to make more power off of a stock SC, you lean out the fuel ratio a little. That makes more power, right? And if it gets lean enough to produce adverse driving performace, wouldn't you already have a problem with detonation?

I am under the assumtion that a rich condition will lead to the "bog" feel of the car. My personal experience has confirmed this thought as well. I re-sealed my IC tubes and I no longer had the bogging down and missfires under boost. Please shed a little more light as to your thought pattern for us who are not as car wise.

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Sam,

It is possible to be starving the engine for fuel enough to create a bogging condition without throwing a CE light. My car was doing this after installing 38# injectors and attempting to run at stock fuel pressure. I also thought it was running too rich, but it wasn't. The only reason I can come up with for why it didn't throw a code, is because at WOT the o2 sensors are ignored. No you won't always get detionation on a lean running engine.

It ran fine at start up and part throttle, but if I pressed the gas too quickly it bogged very bad and felt as if it lost nearly all the power, it didn't buck, miss or ping it just fell on it's face and then recovered as rpms and boost increased. Increasing the fuel pressure from 40 psi to 43 psi made a dramatic improvement. It went from bogging to burning the tires...anyhow I still think it's worth checking the fuel pressure. Running lean only makes more power under certian conditions and to a certian point and then it looses power.

More power comes from the ability to burn more fuel...nearly every performance mod we make to the intake and exhaust system is to allow a greater amount of air flow in and out of the engine which allows us to burn more fuel.

David

i heard somewhere that platinum plugs are no good in higher compression engines. because the high octane gas burns so hot that the platinum plugs will get super got and wont cool down as the engine will, then they mess stuff up. im not sure though. if it works for you then dont fix it! lol

David Neibert said:

I think you don't have enough fuel pressure. It could be very simple, like the vacuum/boost refrence hose going to the fuel pressure regulator isn't attached or is leaking. The regulator itself could be bad, or the pump isn't providing enough flow under high pressure.

David

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Thanks for all the responses!

Dave - wheres this vac hose at? I've checked them all (that I could find) and they all look great.

I'll also be changing the plugs once again this weekend, so hopefully after that, a fuel pressure test, and some new gaskets for the ic tubes I'll have a way to steer myself in.

Thanks for clarifying for us Dave. That helps fill in some of the missing pieces...like anyone will actually be able to put the whole puzzle together though... I didn't realize that at WOT, the O2's are ignored. Shows how much I know about the EEC operations. My '89 may then benefit from testing the fuel pressure as well. It's not as fast as my '92, but my '92 has some other go fast parts on it too...

SLP007, hopefully with this you'll be on your way to a faster SC. Keep us posted.

SLP,

The vacuum line attaches to the top of the fuel pressure regulator, which is located on the fuel rail behind the intake manifold adaptor (casting that attaches to the lower IC tube). It is very difficult to see or reach without removing the wiper motor cover.

The other end of the vacuum hose should be attached to the back of the intake manifold adaptor.

David

Two issues I had that caused that problem over the years was bad plugs(I dont think that sit anymore) and not enough voltage to fuel pump causing bad pressure...Plugs I go with Denso iridium IT20's..Pump wise a 155 lph or higher will be fine if need be changed.Its good insurance regardless on an old car:O)..Of course check for boost/vacum leaks


When did this boost miss problem start?

Just a little update on my 94 that would miss at boost. It turned out to be the fuel pump. I bought a fuel pressure gauge and was sure that it was fine and it had plenty of pressure. Under boost was a different story. I pulled my hair out with this as my car has 90k. Im thinking 94-95 had this bigger pump that had problems as it got old. Just my .02

well i been having the same problem, and for some reason , i suspect the fuel pump, i did motor mounts , fuel pump and balancer at the same time m and after that i been having the problem.

now i suspect the shop could have stole my 255lph pump and replace it with a standar bird one im gonna change plugs and wires and if problem still there ill buy a new 255lph one and install it myself.