Don Christensen

I am not sure if the this is the correct forum for troubleshooting, but it seems to be the best fit.
My wife has an 89 Formula 350 TPI that has been an absolute jewel until recently.

My brother GAVE it to us last year when it turned 195,000 miles because I had always done his mechanic work and he wanted somebody to take care of his baby. My wife surprised me by grabbing the keys, and she, not me has driven it ever since. BTW, we also have a 90 Formula and a 90 Camaro.

Anyway it is now idling poorly and has a definite loss of power. The crisp throttle resonse is gone, and so is most of the fun. Coil and distributor cap are new, as well as good wires. The only thing I have done to it recently is to wire a permenat resistor across the VATS to correct an itermittent starting problem. And last week I replaced a bad fuel pump.

My question is, how do I go about troubleshooting it? I have been repairing cars since age 12, and am now 51. After this many years, I certainly am not going to start taking them to the dealer now.

Many thanks - Don

airdeano

don,
easiest items to check:
fuel pressure, spark plugs (condition), computer scan.
the scan can show relative information in real time. use of
an auto xray, or borrowing a scanner. not just codes but
what the O2 sensore sees, TPS maladjustment, knock sensor
activity, etc...
since the fuel pump has been replaced, and im sure the filter
has too. high mileage engines consider timing chain slack.
easy checks with minimal money spent.
airdeano

72LT1VETTE

What was the reason for changing the fuel pump? Was car running OK before changing pump? Trying to disect your problem. You said it was running like a "jewel" and all of a sudden you change the pump, had to be a reason.

Don Christensen

Hi 72LT1 Vette,

The pump died at 198k miles. It had already been running poorly at that time.

Question; how do I check out the mass air flow sensor?


Thanks - Dom

72LT1VETTE

Can't answer that one. I have speed density, no MAF. Go to the technical section on this site. Some great stuff there.

SLOW5.0

My 90 formula LB9 is doing the same thing. Checked
the fuel press its around 45 with vacume line off.
new plugs, new ac delco cap and rotor. I had to change the TPS out a few months ago but ran fan after that for about a month. changed the O2 sensor. I have ordered a new summit coil and a new set or taylor wire. I dont know what to do next.



PS I am thinking injector ????????

EDGE

Here's a couple of ideas to try. First. Check your pickup coil. Its simple and youll need a Multi meter to test it. I can email you digrams on how to do it from the shop manual. The coil litterally falls apart and gets all gummed up with oil. Its a bit of a you know what to change in case youve never done it before. But it does require you removing the distributor and dissambling it. The second thing is to remove the throttle body off the plenum. Take it apart and clean out all the crap. I had the same problem with a lousy throttle response and this cleared it up. Theres so much gum in there. Just in fron of the throttle blade is a little whole where air channels through the idle air solenoid and it gets all carboned up and so does the Idle Air Solenoid. Also you should be able to see a small crack of light under the throttle blades if you were to hold it up to the light. Chances are the the whole unit is filthy inside of it. Its pretty simple to do I even reused the gasket. Bur it made a world of difference. But be sure and check that pickup coil. If its hooped then the whole ignition system is degraded.

Just a few ideas. Good luck

mckenzie

hello, check fuel pressure!!!! make sure you didn't put in a fuel pump for a tbi 9-13lbs, compared to tpi mid 40lbs

SLOW5.0

Wellll shot mine was the plug wires....... man like nite and day

Morley

With engine running and vacuum line off the regulator it should be 75 psi. That's the first place to look

~M~

Bort62

Wrong.

Try again.

Don Christensen

SPARK PLUG WIRES


The plug wires were breaking down under a load and causing the idle to fluctuate all over the place. I disovered it when I got zapped while checking fuel pressure.


Thanks for all your help, Third Genners!!!!!!:hail:

Morley

That is directly from the GM manual for TPI and also from several other sources. Also I have personally checked checked it and it is correct, 75 psi deadhead pressure.

~M~

SLOW5.0

Don looked like we shared the same problem. What plug wires did you get? I ordered some taylors from summit and I be happy as a pig in chit with them

Don Christensen

Good Morning SLOW 5.0 !!!! When you have kids in college, you are artificiallly impoverished, and look to save $$ every chance you can.

Although I am an engineer, I do a ton of mechanic work for family, friends, and people in our church who do not have the resources. And I have discovered over the years that factory wires are extremely reliable. With the exception of Accels, Taylors and a few others - most replacement wires are cheap, junky, and only last a few years.

Our family owns two Firebirds and a Camaro, so I go to a junkyard about once a month for different things. And when I see a good set of wires on a late-model bad motor, I can usually get them for two or three dollars. Hopefully after our daughter graduates, we can go back to buying the good stuff. I know that the Taylor wires, though expensive, will definitely worth it.

72LT1VETTE

Dead head pressure is solely dependent on the output of the fuel pump. Can range from 40 psi to over 100 psi with aftermarket pumps.

SLOW5.0

Don cant blame you for saving a $$. I need to spend more time in the bone yard myself.