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'90 Chev Beretta 3.1L V6 choking under load @ operating temp

4K views 21 replies 6 participants last post by  psguardian 
#1 ·
Friend is trying to lend me a car (cuz my Trooper isn't done yet), but the catch is that we need to get it road worthy before I can borrow it.

Rig: '90 Chevrolet Beretta 3.1L v6 5spd.
Issue: stalls during warm idle & while driving
Attempted fixes:
Fix 1- check injectors for shorted electronics
Result- All injectors look clean & have resistance within spec

Fix 1a- TBI gasket & EGR gasket died while removing plenum to check injectors, they where replaed. Plenum gaskets are metal w/rubber rings around the 6 ports, still in good shape = cleaned & reused. Issue persists @ idle & driving.

Fix 2- check thermal vacuum valve
Result- Looked caked & didn't extend/retract its full travel = replaced.
_____Now car will idle just fine but still chokes under driving conditions

I don't wanna throw my or my friends money at this blindly, anyone know if this is the same 3.1 that was in early Zu's? any idea what else could cause it to idle great & fail under load?

TIA,
~psguardian
 
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#3 ·
Throttle position sensor?
 
#4 ·
Check the forums at 60degreev6.com? That's where I got most the help for my Trooper engine project. Most the 60degree smart people here are also there.

FYI, I think those 5-speeds are rare.
 
#5 ·
#6 ·
Red0ktober said:
you Sir are the man! My buddy was ready to drop $275 on new 17# injectors. We will go through the code reader & if it gives no leads check all the input sensors.

I don't really want to join another forum for a borrowed car but I think i will go lurk a bit. Anyone else with an idea please chime in.

~psguardian
 
#7 ·
Ok so I spent a good 3 hrs with the Beretta yesterday (sick though I am, I need it to drive to work 2 days a wk). The MAP & a thermal vacuum control valve & one other sensor on the TB have been replaced (before I got my hands on it), I checked the air temp sensor in the air box, the TPS, the injectors when hot... All check out fine. The only sensors I haven't gotten to are the o2 & the coolant temp senders for dash gauge (known to be bad) & the one for the ECU.

The car drove around great for 30min before it started to cut out on me. It was over heating (it felt like an over heated motor at least). Kept the heater on HIGH & the vent was hot enough to burn my hand from 18-24" away. Treating it like an overheat I rolled the windows down to keep from cooking myself & drove low RPMs coasting in neutral as much as possible & avoiding stops 90% of the way back to the house. Grabbed the hose & bathed the radiator. It reacted well to this, loss of power was mild & intermittent on the way home, telling me that it truly was hot. I noticed that the fan NEVER kicked on for the radiator.

I think either both coolant temp sensors are shot & therefore leaving the ECU thinking the engine never warms up fully (messing with fuel/air map to cause overheat?) or the ECU is going out.

Until the overheat kicked in my overall impression of the beretta was GREAT, it has 295k on the orig 3.1 v6 & 5spd. No smoke or ruff idle or anything. One fine motor for that little light weight car.

~psguardian
 
#8 ·
The fan may be switched off the ECU, not it's own sensor. Could be that the CTS is faulty. I don't think they're all that expensive.
 
#9 ·
Red0ktober said:
The fan may be switched off the ECU, not it's own sensor. Could be that the CTS is faulty. I don't think they're all that expensive.
that is one possibility I have noted above (It all makes sense in my head but may have typed it out poorly). I am eagerly awaiting both new CTS (the one for the ECU & the one for the dash gauge).

A side note: this rig originally came with a dash full of idiot lights, thus all the sensors are on/off type sensors, not variable gauge sensors. The ECU is happy with either so the prev owner swapped the dash to one with honest gauges, but not the sensors. The oil pressure gauge pegs to max because the 'idiot sensor' senses pressure, when pressure drops low enough to turn on the 'idiot light' for oil the gauge drops to 0 because its signal is gone lol. We are getting sensors designed for real gauges so no more having to translate dash input by the driver... I am hoping its just the sensors that are bad, not the ECU...

~psguardian
 
#11 ·
Nope, its entirely heat related, but sporadic. Something is failing when hot, just not sure what. It has been well maintained & adult owned its entire life. I thought it had a 50-60k mi rebuild under the hood when I drove it the other day... Friend told me its all orig drive train on that 295k clock! not even blow by from the Oil Fill Port! It still sets you back in the seat, once the tires hook up :wink:

~psguardian
 
#12 ·
They're good engines. Is that a 3rd Gen 3100? I'd like to get a 3100 or a 3400 into a Trooper.
 
#13 ·
Red0ktober said:
They're good engines. Is that a 3rd Gen 3100? I'd like to get a 3100 or a 3400 into a Trooper.
it has a production date aug/90 so its a '91 model year, I think that was Gen 2 (Gen 3 was called the 3100).

~psguardian
 
#14 ·
Then I got your fix. Swap it to a 3400! Should be fun with a 5-speed.
 
#15 ·
LOL its a side mounted v6, I don't wanna swap that, besides this will just be a matter of sensor hunting, upgrading the motor would be more of a pain (not to mention I don't think there is a 3400 that has been treated as well as this 3.1 shy of a crate motor) It would also be way spendier then a new round of sensors.

~psguardian
 
#19 ·
by chance is that the 3.1 TBI engine? the engine in my rodeo is doing nearly the same thing. Idles great when cold then after warm up it bogs and spits on its self, pull over let it settle down, rev it a bit and then take off. its good for a few more miles then, the same again
 
#21 ·
MercuryMan95 said:
by chance is that the 3.1 TBI engine? the engine in my rodeo is doing nearly the same thing. Idles great when cold then after warm up it bogs and spits on its self, pull over let it settle down, rev it a bit and then take off. its good for a few more miles then, the same again
So is it overheating or just running bad, I had problems with my 2.8 starting great and runnning great for 10 miles or so and then start missing. Turns out is was the distributer module. Lost the heat disapating past under it and would get hot and start messing up. Could not find the paste and ended up replacing the module because it came with new paste and that ended the problem until the dist crapped out completely months later. Ended up replacing the dist completly and it came with a new module too. Still ran good until I pulled the engine a month ago to start replacing it with a built 3.1
 
#22 ·
It will run fine for a random amount of time, then starts stumbling under load. Have to keep low rpm & put heater on high to regain power. I will look into faulty ignition system parts though. The gauge cluster was switched from idiot lights to real gauges, but none of them work so im running completely blind.

~psguardian
 
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