Help with an 89 TPI please
Thread Starter
Pro
Joined: Jan 2010
Posts: 611
Likes: 28
From: Olympia WA
Help with an 89 TPI please
So I have an 89 Trans Am GTA with the 5.7. 38k miles. Completely stock. The problem is it runs rich once warm, around 160-170 is when it starts running very rich; to the point of black smoke. The car runs perfect when cold. The engine coolant temp sensor and o2 sensor had been replaced. All other sensors seem to be working fine including the MAF. Injectors ohm out fine. I checked fuel pressure and its at 41-43 psi. The kicker is the pressure drops kind of fast, with in 5 minutes the fuel pressure is around 36-38 psi after the pump kicked on. Goes down to about 28-30 psi after 15-20 mins. This sound like a leaky injector? Any other ideas? Oh, and no codes.
Last edited by syco_cop; Jun 7, 2011 at 11:04 PM.
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
The Multec Fuel injectors in your 1989 Trans Am GTA are very well known to have incompatibility with today's alcohol additive/ E10 gasoline.
You have at least 1 fuel injector leaking down if not multiple injectors failing.
Be best to replace them all with more modern E10 compatible fuel injectors.
Most C4 Corvette guys use the BOSCH 3 injectors.
Other choices out there too for a GM TPI Firebird TA, Camaro, & Corvette.
You need a 21.5lb to 22 lb per hour fuel injector for your GTA.
Research on your own to be sure of the lbs/hr rating required.
BR
You have at least 1 fuel injector leaking down if not multiple injectors failing.
Be best to replace them all with more modern E10 compatible fuel injectors.
Most C4 Corvette guys use the BOSCH 3 injectors.
Other choices out there too for a GM TPI Firebird TA, Camaro, & Corvette.
You need a 21.5lb to 22 lb per hour fuel injector for your GTA.
Research on your own to be sure of the lbs/hr rating required.
BR
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
Next time your GTA is fully warmed up/ coolant temp hot & starts to act up....
Recheck all 8 Multec fuel injectors before the engine has a chance to cool down ( within 10 minutes).
Those GM Multecs 9 out 10 times resistance check very much different Hot from cold readings.
Sometimes as much as 9 or 10 ohms difference.
Sometimes they near dead short out( internal bobbit copper coil windings) after HOT.
You may read some near 1 or 2 ohms or even "0".
Speak from almost 20 years of experience troubleshooting & repairing GM Vehicles with "MULTEC" style fuel injectors.
They POS's with today's E10 Gasoline.
BR
Recheck all 8 Multec fuel injectors before the engine has a chance to cool down ( within 10 minutes).
Those GM Multecs 9 out 10 times resistance check very much different Hot from cold readings.
Sometimes as much as 9 or 10 ohms difference.
Sometimes they near dead short out( internal bobbit copper coil windings) after HOT.
You may read some near 1 or 2 ohms or even "0".
Speak from almost 20 years of experience troubleshooting & repairing GM Vehicles with "MULTEC" style fuel injectors.
They POS's with today's E10 Gasoline.
BR
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Mine showed normal when cold. Two were WAY off when hot. Because one wasn't working on the side where the O2 "sniffs" the mixture, it "thought" the motor was running lean. So, it compensates by increasing injector pulsewidths which adds more fuel.
My cure? I built a 383 and replaced the whole damn motor. THAT fixed the problem!
Thread Starter
Pro
Joined: Jan 2010
Posts: 611
Likes: 28
From: Olympia WA
Thanks for the replies. So what you guys are saying is its most likely the injectors and not something else I haven't thought about? I wouldn't think a week coil or ignition module would give me the symptoms I'm talking about.
Instructor
Joined: Nov 2009
Posts: 164
Likes: 2
From: Spring Texas
Just went thru this with my 95 LT-1 Corvette. Multi-Teq's were leaking at 85K miles. Call Jon Banner at FIC, 770-888-1662 and talk to him about either new or rebuilt Bosch Gen III injectors. Simple change out and my car has never run that good and smooth. I should have done this years ago when I first bought her. Rebuilts are $189 and new Gen III's are $339. Based on the experience sited on this Forum I chose the rebuilts. Good Luck.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
So I have an 89 Trans Am GTA with the 5.7. 38k miles. Completely stock. The problem is it runs rich once warm, around 160-170 is when it starts running very rich; to the point of black smoke. The car runs perfect when cold. The engine coolant temp sensor and o2 sensor had been replaced. All other sensors seem to be working fine including the MAF. Injectors ohm out fine. I checked fuel pressure and its at 41-43 psi. The kicker is the pressure drops kind of fast, with in 5 minutes the fuel pressure is around 36-38 psi after the pump kicked on. Goes down to about 28-30 psi after 15-20 mins. This sound like a leaky injector? Any other ideas? Oh, and no codes.
Have you changed/cleaned the MAF sensor recently?
It could be a failing injector but your indicating the car is fine in "open loop" but once the car goes into "closed loop" you have a "rich" problem (black smoke) so to me it seems more than likely you've got a bad/wacked out sensor in the mix.
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Team Owner
Joined: Oct 2004
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From: altered state
St. Jude Donor '05
It was the injectors. Dont even bother trying to clean them.
Toss them in the trash and replace.
Racer
Joined: Apr 2011
Posts: 296
Likes: 1
From: Tipp City Ohio
Jon Banner
Corvette Injectors
http://www.corvetteinjectors.com/
or
FIC
http://fuelinjectorconnection.com/
