Ok guys ... long time no type !!!! :\

As some of you are aware , I often sell parts and cars ... Well I got a 90 Formula
that was running AWESOME !!! but since then
has started to misfire ..so as I always do .. I performed a full tune up thinking it was the usall bad ignition component ..replaced all the wires , plugs , air filter and trans and motor oil while I was at it ... still misses ... threw a used
distrubutor in ... checked the vacuum , smooth ~16lbs , so that should rule out any valve train problems ... still misses ... checked the TPS ..functions ..no adjustment on a SD car :\ ... so I pull the MAP sensor wire to throw it in open loop ... still misses .. so I look a little deeper into the car ..turns out it has FORD injectors ... hhmmm must be the SVO injectors ?? fuel pressure is at 42 at idles and goes up to 50 or so at rpms ... the car runs so bad that it won't pull beyond 4k :| ... at this point my only guesses are plug cats or a bad injector !! anyone in Atlanta have a autotap I can beg/borrow/buy ???? I've had to send 3 possible buyers away

thanx

TVP

 

TVP,

O.K. - you hooked me with the "Lots of details" line. That always makes suggestions a lot easier to make.

Lacking a scanner, you might want to try the power balance method of determining injector flow. A scanner will tell you what the injector pulse width or "open time" is, but without SFI, the injectors are all fired at the same rate and time (in banks).

Remove an electrical connector from one injector at a time and monitor idle speed and quality. The ECM will react quickly to correct the target idle speed, but cannot compensate for the lack of fuel and resultant miss. Whichever injector(s) doesn't cause any idle change is the likely suspect. If you have spark plug wire pliers, you can verify the diagnosis by disconnecting that same cylinder's spark plug wire. Again, there should be no change if the injector is not opening.

------------------
Later,
Vader
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"Get UP - Drop the bombshell!"
Adobe Acrobat Reader

 

First of all, I hope it pulls 16in.Hg of vacuum rather than 16psi. That being said, your vacuum sounds a little low for a 350 TPI to me. I'm thinking somewhere in the neighborhood of 18-21 in.Hg for a stock 350 TPI. So someone has slapped a cam in there, and also, if those injectors are the 24# SVOs then you'll be running way too rich at WOT, causing the loss of power. These are just some things to check for and hope this helps. It's strange that it ran fine and doesn't now.

------------------
1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley AFPR, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Ruger P95DC, hot wife, new oil filter, thick rubber floormats, no cats.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

 

If I read your post correctly, it appears that the car was running well before. If true, then we can assume that the car has not gotten a new cam overnight.

However, Jethro is correct about the vacuum level. I get between 18-21 in/hg. Closer to 18 if the car is drive (but not moving) and closer to 21 with the car in park.

So you may have a vaccum leak that has developed. I would check that possibility out.

On the fuel issue you say that fuel pressure is 42 psi at idle and 50 at certain rpms. Did you remove the vacuum line from the fuel pressure regulator to check the pressure? Your pressure sounds a little high. In fact, I would not want to run my fuel pressure over 50 psi as it will decrease the life of the fuel pump. I like around 46-48 psi (measuered with the vacuum line off). It makes the fuel pump and injectors last longer.

Also, if you haven't done so, pull EVERY SPARK PLUG to see if you can isolate an individual cylinder. It should show up immediately as either darker than the rest and possibly wet with fuel.

[This message has been edited by Glenn91L98GTA (edited August 19, 2001).]

 

Hey guys ....

Thanx for the replies !!! .... I tried the pulling wires method ..but... I had to pull 2 or 3 to see any difference in idle quality ..even with the IAC un-plugged :\ you were right about the psi/" thing .. I'm
still licking my wounds from the full tune up :| wasn't thinking to clearly As I always say ..when in doubt ..IT'S NEVER THE INJECTORS :\ ...so today I'm going to hack
the exhaust :\ ... I'll let you know what it ends up being :\

thanx

TVP

 

Before you undertake any more work, I strongly encourage you to check the spark plugs first. They truly are your "eyes inside the engine". It can avoid a lot of "needless work".

It wouldn't be the first time that either a plug or plug wire was a "little loose" which caused a miss (sometimes only under certain driving conditions). I also like to measure the resistance of every plug wire from time to time, to see if one is "out of spec".