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1993 Plymouth Acclaim Engine runs so rich it blows carbon c

Tiny
MARTIANENT
  • MEMBER
  • 1993 PLYMOUTH ACCLAIM
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 85,368 MILES
I have been working on a 93 Acclaim for a while now. It was bought off-lease by my gram back in 96, and it obviously hasn't been driven much since then. Since it sat for a while on a cruddy driveway, many things got rusted out, including the engine oil pan (2.5 VIN K, TBI), and the oil pan ended up with a pinhole in it, and losing all of it's oil, while driving one day. The engine was replaced, and ever since, the car has not been right at all. It seriously lacks power (I know 90 or however many HP ain't much, but this is BAD), burns through 10 gallons of gas in 160 miles on the highway alone, and it's just, well, like I said, not as it used to be before the engine was replaced. Now, I have gone through school to become a tech, even though I don't have a job as one at this point, so I understand the basics. I heard a while back, while attending school, that there is a shuttle valve in the throttle body that has a hand in controlling the fuel pressure in Chrysler TBI units. The tech involved was one of my instructors, and he had dealt with a similar problem on a New Yorker, I think it was, that already had the pressure regulator replaced TWICE and came back again for the same issue. I was thinking, that since this car is going to be gotten rid of anyways after I'm done driving it while replacing the fuel lines in my car, that this needs to be fixed as cheaply as possible, and the FPR is rather expensive. I'd rather get the engine running properly while I'm doing the brake work as opposed to having the car haunt the garage again when I should have just done everything at once in the first place.
Can anyone shed some light on the Chrysler TBI unit and how it controls fuel pressure?
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Sunday, December 7th, 2008 AT 8:51 PM

8 Replies

Tiny
DAVE H
  • MECHANIC
  • 13,384 POSTS
Fuel Pressure Regulator
Fuel pressure regulator is a mechanical device located on top of throttle body on Throttle Body Injection (TBI) models or on fuel rail on 3.3L and 3.8L Multiport Fuel Injection (MPI) models. See Fig. 2 . On 3.8L MPI models, regulator attaches to fuel return tube at rear of engine below intake manifold plenum. On all models, regulator is controlled by manifold vacuum. Its purpose is to maintain correct fuel pressure at fuel injector. A spring-loaded, vacuum assisted diaphragm is located inside pressure regulator.
When fuel pump is energized, fuel flows past fuel injector into fuel pressure regulator. Regulator restricts fuel from flowing any further until proper fuel pressure is reached.
When proper fuel pressure is reached, pressure pushes on a spring behind diaphragm. As pressure moves spring and diaphragm, a return line to fuel tank is uncovered. This allows excess fuel to return to fuel tank, keeping fuel pressure constant across injector.
During acceleration, vacuum to diaphragm drops off. Without vacuum assist, spring pressure only acts upon diaphragm, resulting in a slight increase in fuel pressure before return port is opened.
Fig. 2: Locating Fuel Pressure Regulator (3.3L & 3.8L)
Courtesy of CHRYSLER CORP.


https://www.2carpros.com/forum/automotive_pictures/266999_fuel_6.jpg

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Monday, December 8th, 2008 AT 6:48 AM
Tiny
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That didn't help much. I have MPFI on my 87 Firebird. I know how the fuel pressure regulation system works. I would like to know why there is TOO MUCH pressure at the TBI injector, CONSTANTLY. This TB was on the original factory engine that ran properly, right up to the day it was removed, and I KNOW for a fact that the junkyard engine that was installed as a replacement is also a 2.5 (oil pan has been off and 2.2L engines don't have a balance shaft assembly). There is really no reason why this engine is running the way it is--the car has the same TBI unit as it has had since it left the factory floor, the fuel injector has not been replaced with a different one. I can check the vacuum source to the FPR, but I do not believe that the FPR is at fault. I would prefer to hear from a factory tech here, but I guess that isn't going to happen.

I guess what I want to know is if there is a secondary device to control the fuel pressure, as was told to me by a senior technician at my school.
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Monday, December 8th, 2008 AT 11:37 AM
Tiny
DAVE H
  • MECHANIC
  • 13,384 POSTS
You asked for and was given an explanation of the TBI system on this vehicle?

Can anyone shed some light on the Chrysler TBI unit and how it controls fuel pressure?
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Monday, December 8th, 2008 AT 12:20 PM
Tiny
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Where is the fuel pressure relief/rollover valve and what does that do? You never mentioned that---I had to look at the online AutoZone repair manual to find that. And, of course, it doesn't tell you where it is, it just tells you to look up the relief valve under the heading of the rollover valve, which the Fuel System section doesn't have?

Is there an easy way to check the FPR, seeing as how it is basically completely integrated with the TBI unit and doesn't have an external vacuum source to check?
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Tuesday, December 9th, 2008 AT 7:35 PM
Tiny
DAVE H
  • MECHANIC
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Again you never asked about FPR/Rollover valve? They are not integrated into the TBI they are located on the fuel tank? The FPR only releases pressure from the tank the rollover valve is there in case of vehicle rollover? To release pressure from throttle body

Throttle Body Injection (TBI)
Slowly open fuel tank cap to release pressure in tank. Disconnect 2-pin injector connector at edge of throttle body. Connect a jumper wire between injector connector (injector side) Dark Green/Orange wire and battery positive terminal.
Connect another jumper wire to injector connector (injector side) White/Dark Blue wire. Momentarily ground jumper wire connected to White/Dark Blue wire no more than 5 seconds. Injector will energize open, relieving fuel pressure. Remove jumper wires. Fuel pressure is now released.

FUEL PUMP & FUEL PRESSURE REGULATOR TEST
WARNING:Perform fuel pump test with fuel tank at least half full. Before disconnecting fuel line, relieve fuel pressure.

2.2L TBI, 2.2L Turbo, 2.5L TBI & 3.0L
Relieve fuel pressure. See RELIEVING FUEL PRESSURE under FUEL PRESSURE. On 3.0L, disconnect vacuum hose from fuel pressure regulator before checking fuel pressure.
On 2.2L TBI and 2.5L TBI, fuel pressure regulator is not vacuum assisted. On all engines, disconnect fuel supply hose quick-disconnect connector from chassis lines at engine. Connect Fuel Pressure Gauge (C-4799) to Fuel Pressure Test Adapter (6539). Install adapter between fuel supply hose and chassis fuel line.
CAUTION:DO NOT activate fuel pump for long periods, or engine may hydrostatically (liquid) lock.

Using Diagnostic Readout Box (DRB-II), turn ignition switch to ON position. Select ASD FUEL SYSTEM TEST mode. In this mode, DRB-II energizes Auto Shutdown (ASD) relay, causing fuel pump to activate and pressurizing fuel system.
Note fuel pressure, and record reading. Relieve fuel pressure. Remove fuel pressure gauge. If fuel pressure is within specification, fuel system is functioning properly and further testing is not required. See FUEL SYSTEM PRESSURE SPECIFICATIONS table.
If fuel pressure is greater than specification, go to step 8. If fuel pressure is less than specification, install Fuel Pressure Gauge(C-4799) and Fuel Pressure Test Adapter (6539) in fuel supply line between fuel tank and fuel filter.
Repeat ASD FUEL SYSTEM TEST. If fuel pressure is at least 5 psi greater than fuel pressure recorded in step 4, replace fuel filter. If no change is observed, gently squeeze fuel return hose.
If fuel pressure increases while squeezing fuel return hose, replace fuel pressure regulator. If fuel pressure does not change while squeezing fuel return hose, problem may either be a plugged fuel inlet strainer or defective fuel pump. Repair as necessary.
Disconnect fuel return hose from fuel pump at fuel tank. Connect Fuel Pressure Test Adapter (6541) to fuel return hose. Place other end of adapter into an approved 2 gallon gasoline container.
Turn ignition switch to ON position. Repeat ASD FUEL SYSTEM TEST. If pressure is now correct, replace fuel pump assembly. See FUEL SYSTEM PRESSURE SPECIFICATIONS table. If pressure is still greater than specification, deactivate fuel pump. Remove fuel pressure test adapter, and connect fuel pump return hose.
Disconnect fuel return hose from chassis fuel lines at engine. Connect Fuel Pressure Test Connector Adapter (6541) to fuel return hose. Place other end of hose in an approved gasoline container. Repeat ASD FUEL SYSTEM TEST.
If pressure is now correct, check for restricted fuel return line. If no change is observed, replace fuel pressure regulator.
FUEL SYSTEM PRESSURE SPECIFICATIONS
Application(1). Psi (kg/cm2 )
2.2L TBI & 2.5L TBI.39 (2.7)
2.2L Turbo, 2.5L Flexible Fuel & 3.3L (VIN T).55 (3.9)
3.0L, 3.3L (VIN R), 3.5L & 3.8L.48 (3.4)
(1)Specification given is with fuel pressure regulator vacuum hose disconnected.
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+1
Tuesday, December 9th, 2008 AT 8:54 PM
Tiny
MARTIANENT
  • MEMBER
  • 6 POSTS
This is going to sound like an even dumber question, but:
Is it possible to install some sort of in-line tap where I DON'T have to have a Chrysler factory gauge to take fuel pressure readings? I have a gauge, but it's for engines already equipped with a test port.

And, if the other valve is in the fuel tank, then I guess that's not it, either (fuel tank has been replaced since), which brings me to my original question: IS THERE A SECONDARY DEVICE, BESIDES THE FPR, THAT REGULATES FUEL PRESSURE, AS WAS TOLD TO ME BY AN INSTRUCTOR?
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Tuesday, December 9th, 2008 AT 10:32 PM
Tiny
DAVE H
  • MECHANIC
  • 13,384 POSTS
There are in-line T pieces you can buy. My kit came with one as standard. I just connect it in-line. Remove it when finished checking pressure and reconnect fuel hoses together. There is no other device on vehicle to regulate fuel pressure. If you think the throttle body is not working correctly. You need to replace it. There is no mention anywhere in tech data of a "shuttle valve".
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Wednesday, December 10th, 2008 AT 8:47 AM
Tiny
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I'll have to check the lines and all of that when I get the car into the garage. I'll even check the return passage in the TB. Worse comes to worse, I'll have to remove and disassemble the TBI unit and soak the main body in solvent to see if that clears out whatever is clogging the return passage.
I'll have to see if I can't snag a TBI unit off of a car at my favorite J/Y sometime, if they still have one.
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Wednesday, December 10th, 2008 AT 6:19 PM

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