1989 Beretta GT 2.8L Intermittent Stall

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mh180005
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1989 Beretta GT 2.8L Intermittent Stall

Postby mh180005 » Tue Dec 24, 2019 4:50 pm

We are the original owner of a 1989 Beretta GT 2.8L 5-speed with 240,xxx miles. The car intermittently stalls when driving and it seems worse only when the motor is operating at normal temperature. This happens at highway speeds, city driving, or at idle. It will start right back up but then may, or may not, stall again. When running it has plenty of power and doesn't miss or stutter. I've kept pretty current with plugs, plug wires, etc. I had a local shop check the fuel pressure and received an OK. An engine light does not come on. The local shop is very helpful and is concerned about replacing parts that may not be the problem however they think the ECM and/or coil packs could be at fault. I'm very handy and can begin to replace the easier parts myself which is why I wanted to get help on what the Beretta forum may think I should start with. Any ideas?



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Rettax3
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby Rettax3 » Mon Dec 30, 2019 2:24 pm

I would be looking at the IAC, or Idle Air Control Valve, as you seem to have no other symptoms. The valve itself may not even be the issue, but possibly the air passages it controls. Due to the PCV system, the IAC can become clogged with carbon and sludge deposits over time. New parts often do not work correctly in the older cars, so I would recommend first trying to clean of the IAC and use a pipe-cleaner and some judicious use of carburetor-cleaner (the spray kind) to clean out the air passages. While at it, use an old toothbrush and more careful use of the carb-cleaner to remove all carbon and other build-up inside your throttle-body. Easy, cheap place to start, something your engine can use anyway, so nothing lost. If the IAC does need to be replaced, get only a good quality unit, and be prepared for the Idle Relearn Procedure... Good luck, and I would love to see some pics of your car. Welcome to the site!


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

LisaMartinez
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby LisaMartinez » Sun Mar 01, 2020 4:11 pm

how do you do the idle relearn process???



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Rettax3
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby Rettax3 » Sun Mar 01, 2020 10:09 pm

Here is, I believe, the 'latest and greatest' version of the relearn. Don't worry about the "Techline Scan Tool" blah blah, just run the procedure at the end. Be aware, your car will run without doing this, the 'idle relearn' is simply a 'fine-tuning'. Also, your ECM will relearn by itself after a few miles and maybe a warm-up cycle or two, depending on the driving conditions. The two 'suspect' issues on here is their reference to the 3.4 DOHC engine as an "L01" -it is an LQ1, and this should also apply to the LG5 VIN-V Turbo 3.1 in the '89-'90 Grand Prix models, so I am not 100% convinced this was released by GM -they don't often make that kind of typo or ignore an entire line of relevant engines, but the procedure itself looks close enough to the original procedure to work.
GTU89 wrote:
Diagnosing Intermittent Idle Speed Increases
Group Ref.: Engine Fuel & Emission
Bulletin No.: 476510
Date: May, 1994

INFORMATION

SUBJECT:
DIAGNOSING INTERMITTENT ENGINE IDLE RPM INCREASE

MODELS:
1988-89 BUICK CENTURY AND REGAL
1988-89 CHEVROLET BERETTA/CORSICA, CAVALIER AND CELEBRITY
1988-89 OLDSMOBILE CUTLASS CIERA AND SUPREME
1988-89 PONTIAC GRAND PRIX AND 6000
WITH 2.8L ENGINE (VIN W - RPO LB6)

1989-93 BUICK REGAL
1990 CHEVROLET CELEBRITY
1990-92 CHEVROLET CAMARO
1990-93 CHEVROLET BERETTA/CORSICA
1990-94 CHEVROLET CAVALIER AND LUMINA
1989-93 OLDSMOBILE CUTLASS SUPREME
1989-91 PONTIAC 6000
1989-93 PONTIAC GRAND PRIX
1990-92 PONTIAC FIREBIRD
1991-94 PONTIAC SUNBIRD
WITH 3.1L ENGINE (VIN T - RPO LHO)

1991-94 CHEVROLET LUMINA
1991-94 OLDSMOBILE CUTLASS SUPREME
1991-94 PONTIAC GRAND PRIX
WITH 3.4L ENGINE (VIN X - RPO L01)

1993-94 CHEVROLET CAMARO
1993-94 PONTIAC FIREBIRD
WITH 3.4L ENGINE (VIN S - RPO L32)

1994 BUICK REGAL AND SKYLARK
1994 CHEVROLET BERETTA/CORSICA
1993-94 OLDSMOBILE CUTLASS SUPREME
1994 OLDSMOBILE ACHIEVA
1994 PONTIAC GRAND AM AND GRAND PRIX
WITH 3.1L ENGINE (VIN M - RPO L82)

The following information may assist in the diagnosis and correction of an intermittent increase in engine rpm with closed throttle (accelerator pedal not depressed). Typically there is no malfunction indicator light associated with the condition.

The engine control system sensors are supplied a 5 volt reference signal to ensure properly scaled readings to the engine control module (ECM). If a large current draw flows through the circuit supplying the 5 volt reference, the input signals, as read by the ECM, will be skewed low. The ECM program will store an incorrectly low throttle position sensor signal as zero. If the reference voltage returns to normal, the ECM will interpret the resultant high throttle position sensor signal as an open throttle and idle air control steps (throttle follower) will be added accordingly, causing an increase in the engine rpm at idle.

The A/C pressure transducer has been found to be especially vulnerable to shorts during the engine crank process. Electrical wires in the engine harness that are unprotected and rub on structural members also will cause the problem.

Inspect all wiring and sensors associated with the 5 volt reference signal for shorts and correct as necessary.

If the vehicle also has a condition associated with the air conditioning system, diagnose and correct as necessary.

With a Techline Diagnostic Tool, read the throttle position sensor, manifold absolute pressure sensor, and A/C pressure transducer voltage with the key on-engine off.

If all three voltage readings are skewed below their normal ranges, inspect the A/C pressure transducer.

If all three voltage readings are within normal ranges, disconnect the battery for one (1) minute, reconnect and start the engine. If the increase in engine rpm at idle condition is gone, inspect the A/C pressure transducer.

NOTE: On the LB6 (2.8L VIN W), LHO (3.1L VIN T) or L01 (3.4L DOHC VIN X) engines, If the ECM Is without battery power for any reason, then the Idle air control valve (IACV) position information for a stable satisfactory engine Idle Is "lost" and replaced with a default value. To correct the IACV position Information, perform an Idle relearn procedure using a Techline Diagnostic Tool. You can also manually relearn the Idle by following the procedure below.

1. Remove battery power for one (1) minute. Restore battery power and place air conditioning controls (if equipped) in the "off" position.

2. Firmly apply the parking brake and block the drive wheels. Start the engine, shift the transmission to drive for automatics and neutral for manuals.

3. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

4. Turn the ignition key to the "off" position for at least 5 seconds.

5. Repeat Step 2.

6. Allow the engine to run for at least five (5) minutes.


The correct IACV values for proper idle control will now be stored.




I believe someone may have said about this before but it is different than the one posted in the FAQ.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

mh180005
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby mh180005 » Sun Mar 15, 2020 8:06 pm

Finally had a chance to get back to working on my Beretta. I've tried the following however the same stalling symptom continues:
1) Cleaned throttle body, IAC, and checked visible vacuum lines: car continues to stall

2) Replaced IAC with a new one from AutoZone however I couldn't get car to stay running long enough to do the Idle Relearn Process. I put the initial IAC back on and now the car start but continues to stall.

Any additional ideas?



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Rettax3
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby Rettax3 » Mon Mar 16, 2020 3:30 pm

I think you really need to get into basics on this. Check fuel pressure. (*Edit: I know the shop did, but it needs to be monitored while the failure happens to make sure the pump didn't cut out. Ditto on the spark-check. You need to find out if either fuel or spark -or both- is the cause to know where the problem is. Noid-lighting the injectors to see if they cut out causing the stall would also be golden info here.) Make sure spark is good. Try to pull codes, check for them even if you have no check engine light. If there is any way you can get a cable and laptop on this, or an old Snap-On 'brick', or anything that can read sensor data, you will probably see the cause right away. CTS (Coolant Temperature Sensor)? TPS (Throttle Position Sensor)? MAP(Manifold Absolute Pressure Sensor)? Could even by the CKP (Crankshaft Position Sensor), which would be really hard to see without a graphing scan-tool (or laptop setup with the right software) or a scope-meter plugged in to watch the sensor itself. If the ICM is going out, it could kill spark for a moment, especially when hot, then 'wake back up' and be ready to start the car when you crank it again, which is why the shop suggested the coil-pack (it wouldn't by an individual coil, just the base module, but frequently they want you to replace the whole thing for warranty purposes in case a bad coil fried the module, but it doesn't happen often on Chevys, pretty common for Fords though). Bad ECM could be it too, as they said.

I re-read your initial post, and honestly a bad IAC is less likely if it also stalls at highway speeds too... Right now, the CTS and ICM are your two most likely suspects, followed by the CKP and the wire harness connecting the CKP to the ICM. Really shooting in the dark on this one though... Double check all vacuum-lines and the tiny hose connector to the MAP too, since that could be it, but without any sputtering or other odd behavior, it is less likely. Good luck.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

Bapsu
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby Bapsu » Mon Mar 16, 2020 10:39 pm

Ur car cant stall on hwy if u got bad IAC since ur throttle flap is open while u drive (unless it stalls when ur not pressing throttle?). So when it dies do you press gas or not?



mh180005
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby mh180005 » Tue Mar 17, 2020 10:02 am

Thank you for the replies. This is certainly a difficult problem to diagnose. I spoke to the Service department at my local Chevrolet dealer and they are confident they can determine the problem as they have the diagnostic tools and seasoned mechanics. I'm going to have the car towed (no charge with my insurance) to the dealer and pay the $100 diagnostic fee. I'll report back to this great forum on what they find in hopes that others will benefit.



mh180005
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby mh180005 » Sat Mar 21, 2020 9:30 pm

The local Chevrolet dealer diagnosed the problem to be the Ignition Module is at fault. In addition, the recommendation is to also replace the spark plugs, spark plug wires, and coil pack.

I can easily replace the spark plugs and wires since I've done this before. However, I need help with any instructions on how to replace the ignition module and coil pack.

Please help with any instructions you have to keep this original owner Beretta on the road! :)



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heavywoody
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Re: 1989 Beretta GT 2.8L Intermittent Stall

Postby heavywoody » Mon Mar 23, 2020 7:51 am

You might need to move the starter out of the way, or the oil filter, since these are right under the exhaust manifold on the engine. Either way, there are 2 bolts per coil pack that hold them onto the ignition module. Remove all of those, and disconnect the wiring from the module. Install in reverse - make sure to keep the plug wires in proper order.


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