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Tech501
Tech501, Auto Service Technician
Category: Car
Satisfied Customers: 747
Experience:  38 years exp, ASE Mastertech with L1 Advanced Engine performance
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91 beretta: 3.1 V6, 110,000 miles, automatic..injector..connector

Customer Question

91 beretta, 3.1 V6, 110,000 miles, automatic: Engine Idles rough and kinda shutters under hard acceleration at 3000 rpm. I have checked injector resistance for each bank and each reads between 4.1 - 4.3 ohms (with engine hot and cold). I shorted a&b ports on aldl connector and no codes were stored. What else can I look for?
Submitted: 11 years ago.
Category: Car
Expert:  Tech501 replied 11 years ago.
 It sounds like ignition breakdown to me. How about plugs, wires or coils? Have you done a compression test?
Customer: replied 11 years ago.
Reply to Tech501's Post: I will check the plugs, wires and coils tonite. I'm not worried about compression (I think) because the car ran fine late Sunday and started running rough on Monday morning. I am the original owner and the car has been very well maintained. Oil has been changed on average every 2,000 miles. I have also changed all filters rather frequently in the last 100,000 as well as the fuel filter. I spent some time last night looking for any arcing on the plug wires (in the dark) I see no major issues there, only some minor flickering in the dark. I will visually inspect each plug. I will check resistance across the terminals on each coil pack and I will check the resistance on each plug wire. Does that sound like a correct procedure for a DIY mechanic?
Expert:  Tech501 replied 11 years ago.
 That may or may not find your problem with a DIS sistem. They fire 2 cylinders at the same time and a problem with one could  show up on the other. My first criteria would be age and condition of the wires. If they are oil soaked or over 50K, i would just replace them. The resistence is an accumulated total of 2 wires and 2 plugs. A weak coil will exaggerate a resistence problem.
Customer: replied 11 years ago.
Reply to Tech501's Post: Over the life of the car I have replaced the plugs every 10,000 and the wires every 20,000. I do this because I fear that the steel plugs might otherwise seize since the heads are aluminum. $6 dollars for 6 plugs doesn't break me every year. Every other time that I change the plugs I change the wires which are lifetime guaranteed and no charge.
Expert:  Tech501 replied 11 years ago.
 OK, so that means that as long as you didn't drop or crack one of the plugs or the wires didn't burn on the exhaust, a misfire is very likely a coil. Your idea of checking the resistence of each coil is probably the righ way to approach the problem. The symptoms do act more like a coil anyway. The extra resistence created by the extra load of hard acceleration increases the KV needed to make the jump and you probably exceeded the capacity of at least one of the coils.
Customer: replied 11 years ago.
I took the ignition module w/coils in last night and I had them test it. The guy tested the coil packs and the module. Both were good. He tested the module 6 times and it passed each time. I put everything back. I put new plugs in and new wires. Started her up. Drove around. Problem still there.
Expert:  Tech501 replied 11 years ago.
 Can you be sure what's happening is cylinders dropping out as opposed to the engine falling on it's face due to something like a Mass Air Flow sensor or even a transmission problem?
Customer: replied 11 years ago.
Reply to Tech501's Post: I don't understand your comment. If you are referring to the engine failing - I don't think so. No oil loss, no funny knocks, noises or pings, no smoke and performance is just fine for the first 5 - 10 minutes of driving. Just in case I disconnected my TCC to see if that was the problem. I don't have a MAF but do have a MAP. I will swap with a known good one to see what happens tonite. I did notice that is has been running a little hotter and the fan does not kick on till the gauge hits almost high. It used to kick on in the mid range of the gauge. I did have a problem last year when the SES came on and I determined that the coolant sensor needed replacing but that has been resolved. Thanks for your patience. Sorry if this problem is becomming a burden to you. I need to fix this but I don't have money to take to the shop. Right now I have more time than money.

-Chris.
Expert:  Tech501 replied 11 years ago.

 No Problem, your doing OK.


I didn't mean engine failure I meant the difference between losing power on one cylinder vs a surgiing or severe hesitation type symptom. Can you confirm you are dropping a cylinder and if so, can you pinpoint which one?

Customer: replied 11 years ago.
You were right. It turns out it is a DIS problem. I repeated the same test that the autoparts guy did using an ohm meter but with the coil packs "hot" off the car. One of them is bad when hot but is in spec. when cooled off. I appreciate your help. Could you please help me with one more problem. I will be sure to add a $5 bonus if you will. The car has been running a little hot lately. Usually the fan kicks on 1/2 way between hot and cold on the gauge but lately it doesn't kick on till 3/4 up or higher. I changed the coolant sensor about 2,000 miles ago but I do need to flush the system soon. Either way shouldn't the fan kick on as it always did despite the condition of the coolant. As you know I am strapped for cash right now and I appreciate your help.

-Chris
Expert:  Tech501 replied 11 years ago.
 I really don't think you have a problem with the fan. The dash gauge calibration may have shifted a little. Those fans aren't programmed to come on until approx 228deg. That's pretty hot but completely normal. If you had a scanner, you could monitor the temp the computer is seeing and verify this. You could always turn the A/C on and that will activate the fans all the time. As long as it never goes into the red and immediatly starts coming down when the fans come on, you really don't have a problem. If your really worried that it's wrong, change the 2  wire temp sensor but I doubt it's bad.

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