1988 Beretta misfire when cold and random acceleration

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JackTheFox
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1988 Beretta misfire when cold and random acceleration

Postby JackTheFox » Wed May 09, 2018 6:37 pm

Hey. Yesterday i bought a 1988 Chevy Beretta GT with the 2.8L V6. It has around 150.000 Miles and its in mediocre shape.
When i do a coldstart on it, the engine starts normally but you can literally feel the engine misfire while sitting in it, and just slightly hear it. That gets better when the engine (probably) gets on operation temperature (The temperature sensor is probably bad because the temp only gets up sligtly on the digital cluster).
The other problem (Might be connected to the first issue) when i am driving very slowly up on a hill, and keep my foot stable 1/5 on the gas, the car accelerates more, then less, then more, then less and so on.
My Beretta is one that didnt received an update, so still has the MAF unit on it.

I hope someone can give me help with that :)

Greetings



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Re: 1988 Beretta misfire when cold and random acceleration

Postby ifixalot » Fri May 11, 2018 9:22 am

These engines had injectors that went bad often. When cold, it runs rough but smooths out a little when warm.
You can pull the spark plugs and they should all be very light brown or almost white. If they are all black except
one, which would be lighter the the other five, you have a bad fuel injector. That one plug is where the bad injector is.
You can also get an ohm meter and try to measure the resistance of each injector. They should be about 11-12 ohms each.
If any are below 11 ohms, it is bad and won't fire fuel into that cylinder.
Of course, you could always just have bad spark plugs wires or other things too but those would not improve as the engine warms.



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Re: 1988 Beretta misfire when cold and random acceleration

Postby GT_Indy » Fri May 11, 2018 10:32 am

There was an update for the MAF 88 but it did not omit the maf. I remember because we had an early 88 and its eeprom was changed years ago by the dealer, but still used a maf. There was also a spark plug recall. And something else I can't remember at the moment.

There is the later year 89 no maf eeprom that exists for the 2.8. If you wanted a custom chip to omit maf and maybe egr and stuff WOT-Tech.com is a good place to look.

If it runs bad cold but gets better warm it could be leaking injectors. If it hunts in rpm it could be O2 sensor and/or IAC valve. I remember we had a MAF go bad on the 88 and it made the car unhappy, does it get better if you unplug the maf?

In 1988 they used 2 seperate coolant temp sensors. One on the lower intake for the computer and one on the corner of the head by cylinder 5 for the gauge.
But if you have a digital cluster I'm not sure if that is still the case, you would have to look under the hood to verify if you have the second sensor on the head.


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Re: 1988 Beretta misfire when cold and random acceleration

Postby JackTheFox » Fri May 11, 2018 11:05 am

Hello and thanks for the answers. To check if all the injectors are good, i'd need to remove the intake manifold to get to them right? I'd need to order some gaskets before i can do that, but i'll definitely put that on my list. I only have the car since a few days and was only able to drive it one time, i'll see if i can get a little more detailed informations once i get to know it better.

I think i'll probably just stick with my MAF because that would be the easiest to just let it be. I found a crack in the MAF housing after the "MAF sensor", so i am guessing it draws pirate air at that spot. I have had a whole OEM MAF sensor in the parts box that came with the car, but i am not sure if its used or not. Is there also a way to test its functionality with the ohm meter?? Some values that it should read to be in spec?

The RPM in idle is relatively stable. I dont hear it changing too much, i just has a slight misfire now and then when its warmed up. Barely noticable.
But when i slightly hit the gas and go uphill, the RPM goes up and down randomly, causing the car to accelerate more and less. Could that be a broken TPS ?

I also have a Corsica (89 model) and it does have 2 coolant sensors. I'll have to see if those are on my beretta too. The next time i can check is in a week, since the car is not sitting at my place.
Can i messure the sensors, are there values they should have?

Greetings :)



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Re: 1988 Beretta misfire when cold and random acceleration

Postby GT_Indy » Fri May 11, 2018 11:59 pm

Surging under load. I wish I could remember as I had that problem in the past.
I suggest checking all vacuum hoses and making sure there are no leaks anywhere. Surging under load sounds like a MAP/MAF discrepancy to me but I'm not certain. It could be the crack in the maf like you mentioned, depends if air is getting past.
Does unplugging the MAF and letting it default help at all when driving under load? (The SES light would come on with it unplugged).

In my expierence my tps usually fails with a dead spot at idle and if I tap the gas I get a surge of death then it revs normal.

How is the vacuum controlled EGR? Is it sticking open? Does it open/close okay?


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Re: 1988 Beretta misfire when cold and random acceleration

Postby JackTheFox » Sat May 12, 2018 3:10 pm

Plans changed, i'll get the Beretta to my home on Monday so i can work on it.
I have a fog machine, so i will be able to test the vacuum systen properly. On my Corsica i found a briddle and broken vacuum hose going to the vacuum tank, so thats something to look at. Im also going to replace the TPS since i have a new one laying around anyways. Same with the MAF that i have laying around.
I'll be able to check the rest on monday and the following days then.



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Re: 1988 Beretta misfire when cold and random acceleration

Postby Rettax3 » Sat May 12, 2018 8:19 pm

The digi-cash cars do NOT have a second gauge-only sensor. The cluster receives temp data from the ECM directly, so if your gauge is wrong it could likely be a bad sensor. A bad coolant-temp sensor will definitely cause performance issues, it will not set the fuel delivery right. It is like running an old carbureted engine with the choke operating in random positions. To check your sensors, the best bet is to get an OBD-1 scan tool that can read the data from the ECM through the diagnostic link. That trouble-shoots wring and connection issues too, and helps diagnose the ECM's status as well.

Your MAF is still used as an IAT (Intake Temperature Sensor) even if it had the update -look for a MAP sensor mounted on the firewall or somewhere around the intake manifold -some of the techs got pretty sneaky at hiding those in there.

Good luck, welcome to the site.


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Re: 1988 Beretta misfire when cold and random acceleration

Postby JackTheFox » Sun May 13, 2018 11:05 am

Hello Rettax3. Thank you for that information, i didnt know that. So there should be only a coolant temperature sensor in the thermostat housing? I can check that on Monday or Tuesday for sure.
Is there an adapter available on eBay for the GM OBD-1 connector?
Oh i think i actually found a MAP sensor. I didnt expect that the Beretta has gotten the update. Heres a picture i took a few days ago:
https://imgur.com/a/eUfaphL

So the MAF isn't doing anything except measuring the intake air temperature?

Greetings :)



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Re: 1988 Beretta misfire when cold and random acceleration

Postby Bapsu » Sun May 13, 2018 7:53 pm

Plugs and wires ok? Misfire on low rpms might be caused by bad wires, also if its misfiring more when its humid or cold I would blame wires.



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Re: 1988 Beretta misfire when cold and random acceleration

Postby Rettax3 » Tue May 15, 2018 3:21 pm

You are welcome. In cases like this, especially since you just bought the car and don't know the service history, I recommend a complete tune-up. Plugs, wires, fuel filter, and do not forget the PCV valve, for $2 it can save a lot of issues, it is on the back of the engine in the rear valve-cover hiddent by the intake manifold -be sure not to break the hose going to it, sometimes those get brittle. Check the air filter, all the fluids, and of course do an oil-change so you know it is fresh and a good quality oil.

Good find locating that MAP sensor, so yes, your car has been updated (most of them were). Your surging is quite possibly just the idle relearn going on, especially if the previous owner let it sit, replaced the battery just before selling it, or kept disconnecting the battery before selling the car to keep it from going dead. If your car isn't actually getting to operating temperature (or doesn't think it is getting warm due to a bad CTS (Coolant Temperature Sensor), the relearn process may be problematic or take longer. Search the Board here for 'idle relearn' and you should be able to find a procedure on it, the ECM will eventually figure it out on its' own though. Snap some pics of your car and post 'em up, we wanna see! :good:


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Re: 1988 Beretta misfire when cold and random acceleration

Postby GT_Indy » Tue May 15, 2018 4:36 pm

I wasnt sure if the 1988 digital cluster had 2 sensors or not. The only year Beretta with a digital cluster I owned was a 1990 with the 3.1 v6 which has only 1 sensor.
But our 1988 with analog gauge had the two sensors.

The MAP sensor on the firewall does not verify if it has the eprom update or not. And it does not tell you if you have the MAF updated eeprom or the No-MAF Updated eeprom as there were both.

My families 1988 Beretta GT (they bought it in late 87) at that time got the updated MAF eeprom. But it never got the No-MAF eeprom that came later in 1989.
I dont believe all the 1988's got the No-MAF as my family bought another 1988 Beretta GT about a year ago (someone had a nice one stored away), and it still runs the MAF code.

I suggest getting one of the old scanners to verify what eeprom you have. Years ago the MAF eventually failed on the first 88 GT we had and was sending random values to the ecm. I eventually swapped an 88 No-MAF eeprom into it (cheaper than buying a new MAF at the time) turning the MAF into an IAT sensor. I remember the scanner read all zeros on the 89 eeprom and had air flow values on the MAF eeprom.

The idle relearn can be picky. I have a 94 Sunbird which is an OBD1 3.1 v6 and every time the weather changes it forgets how to run. If I use it in 32'F weather and dont run it till the weather turns to 80'F it wont be happy till I do a re-learn. lol


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Re: 1988 Beretta misfire when cold and random acceleration

Postby JackTheFox » Wed May 16, 2018 9:33 pm

Hello and thanks for the messages :)
I will do a whole service with that car including spark plugs (Even if the ones in look new, but i dont know if they have the right gap), wires, and so on.
The MAF already got replaced yesterday with a better looking not cracked one. I also changed out the TPS til i realised that theres apparently a difference between the 88 and the 89 model. The 88 one is slotted for adjustment, while the 89 one just bolts on as it is. So i had to buy the correct one for that also. Now another question is, how do i adjust the TPS correctly? Just turn it til i feel it catch the throttle? Or any other way?

Also its correct, my 88 Beretta with the digital tachometer has just one temp sensor in the thermostat housing. Since i am going to replace that one and the thermostat, i have a important question. In the book it says bleed out air on the thermostat housing/cover. But there is nothing to bleed it? I did the same a week ago with my corsica, which also doesent have a bleeding screw there. Today i was driving it the first time for a longer period of time, and apparently there was an air pocket trapped, because it was bubbling and puking out some coolant on the street. But how do i get rid of that air pocket if theres no bleeding screw?

I'll also try the idle relearn, i'll probably also have to do this on my Corsica. The idle is alright but not perfect.

And here are some pictures of my 200 € ($ 235) Chevrolet Beretta :)

Image

Image

Image

Greetings :)



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Re: 1988 Beretta misfire when cold and random acceleration

Postby GT_Indy » Thu May 17, 2018 4:27 pm

Great looking car! :)

Ideally you should get an OBD1 scanner and adjust the tps so it reads above 0% then turn it back till it read zero percent. This way its not too far one way or the other.
At leat thats how I've always done it. Never had issues.
If you dont have a scanner to read tps position you could rough it in like a best guess then turn it back as needed.

The coolant you just have to let the air work out on its own. My 1990 Indy after a coolant change I carefully ran it till it got hot enough for the thermostat to open then I added coolant as I could.
Just be very careful because the coolant is hot and under pressure, the cap can shoot off if you arent ready for it.
I opened mine slowly with a thick rag between my hands and the cap so I wouldnt get burned.

You can gap the plugs yourself. Someone else will have to comment on the gap thickness as I dont remember off hand. But I agree a full tune up with plugs, wires etc is helpful for it.
I opt to replace coils, O2, and sometimes the ignition module on my cars as well when I buy them used. The Crank position sensor in my opinion is a toss up, if it works I leave it now because I used to replace them as part of a tune up on my cars and they always got stuck in the block and I could never get them out without working on it for 2 hours; and they always broke in half on me. lol


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Re: 1988 Beretta misfire when cold and random acceleration

Postby JackTheFox » Fri May 18, 2018 4:47 pm

Thank you :) I know the paintjob is very individual, but better than a burned down silver :D

I've been looking and looking on eBay, but the only thing i find is a OBDII to GM OBDI adapter. Not aure if that'll also do the trick?
Okay, so i should just turn it til i feel its catching the throttle. I'll try that then :)

Ohh okay, so there is no other way than to let it boil and somehow let the air squeeze its way out?? It was kinda scary seeing my corsica pushing out coolant and those boiling sounds in the radiator hoses.

I've got myself a spark plug gapping tool, and i know its 0.045" :) The car will definitely get a full tune up before it'll go back on the road.

I have another question. They wired in an aftermarked radio, but they did something wrong with the cables. It always looses memory and i think its constantly drawing power.. To work on the cables that are hanging down bellow the factory radio. But how do i get it out?? On the corsica i just need to pop off a plastic cover surrounding the radio. But how is it done on my 88 Beretta, since there is no removable trim piece around the radio?

Greetings :)



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Re: 1988 Beretta misfire when cold and random acceleration

Postby GT_Indy » Sat May 19, 2018 1:02 am

On the 88 beretta the whole plastic bezel has 2 screws on the bottom in the back. Then it comes off.
Then there are 4 screws that hold tge radio and climate control on; 1 screw on each front corner; bottom screws are ventricle.

There should be a constant 12 volt wire for radio memory and a switched 12 volt wire for radio power. Sounds like they are using the switched 12 volt wire for both (or they simply didnt connect the memory power). Won't know without looking.

Yah with the cooling system there is no easy way to let the air out. I would unbolt the 2 bolts holding the thermostat to try and get the air out but it doesnt remove all of it. Mine got to 3/4 hot then dropped to cold so I knew air came out, and I addedmore coolant. Eventually the rest after that worked its way out.

E
On eBay theremight be a used "Monitor 2000" and get the plug in pack for "1988 Beretta v6".
Or Moates.net and get a data logging cable and you can use it with a laptop and Tuner pro, more complex.
Those are two common options.

I've roughed in the tps before without a scanner. I've noticed once you get a feel for it its usually good enough as long as its close. lol

How is the IAC valve? Sometimes those get plugged with build up and sometimes stick or fail to move correctly. Usually resulting in high idle or stalling.


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