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matt1970

95 GP intermitant miss OBD1.5 question

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New to the forum.Long time reader first time posting sorry if this is the wrong place for this post.

I have a 95 GP se 3100 with an intermittent miss that just keeps getting more common.Miss is like a 3/4 race cam idles.It can come and go,kill the motor at any speed,refuse to restart for 15 min or fire back up and purr.Only constant is it only dose it when the engine is at operating temp after driving more than 4 miles.

what I have tried;

replace comp temp sensor

installed after market fan controller set to 210deg.(Since found Corroded control wire was caused inconstant fans)

Swapped coil from gtp

new plugs and wires

good spark all 6

replace fuel pump and filter (pressure was a little low)

cat vacuum tested and not excessively hot

EGR tested and new seal

Map tested ok

O2 sensor voltage ok

clean throttle body twice

throttle position ok

compression ok and balanced

 

So everything tested good,,,,when I tested it....I have little to no experience with OBD1.5.but can I trust its diagnosis?The service engine light has never turned on.No light = no codes.No code means the computer can't see the problem.There fore I can eliminate everything the computer is monitoring as being intermittently bad.The monitoring list is the same as OBD1? I am down to position sensor or ignition mod fail when warm with road vibration but (correct me if wrong) that will turn on the SEL.

 

Thanks for making it this far in a long post and any help is appreciated.Thanks in advance.I was told by members of grand prix forum you guys were men with the answers!Don't make them liars! lol

 

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A situation where the engine just dies at any rpm/speed is more than a miss. Happening when the engine is hot makes me think of a failing ICM, or possibly a corroded circuit from the CPS that feeds the ICM. That's where I'd start to look for a problem.

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i ditto 55truckers thoughts.  i had this same issue 15 yrs ago.  ended up being the wiring to the ICM was corroded at the 12v/ground side of the ICM itself.  yours could be same, shorted wire in that harness, or CPS wiring as well.  Hopefully an easy find but be prepared to dig into the loom.  Circuit tester would save you tons of trouble.  Might as relocate the ICM to a non stupid spot if you end up going in that deep.

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Might as relocate the ICM to a non stupid spot if you end up going in that deep.

 

It's already on the top of the engine on a 3100. 

 

I'm leaning toward ICM, CKPS, or the associated wiring like 55trucker and GTP091 suggested.  On an MPFI car, I'd suggest ohming out the injectors, but I'm fairly certain a bad injector on an SFI car won't kill the whole bank. 

 

 

Haha hey matt! Glad you made it over! I'm definitely following this one since it has me stumped too. I'm sure digitaloutsider will chime in with help as always pretty soon! :)

 

There are people much smarter than me here  :mrgreen: .. but I'll take it!

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I'll echo the others and say it's ICM related. Your description of the "miss" is a classic example of what can happen with an intermittent ICM. Verify that your wiring is ok to the icm and cps. After this, try to reproduce the failure, then start testing again while the car will not start.

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need to figure out how to turn on notifications on this sight.Thanks for all the responses.I was leaning towards ICM or crank pos.but the no codes,and the intermittent leads to test showing good unless you can reproduce the fail on demand.My son drives the car primarily so we sat down this morning and listed the times and places it dies (or runs really bad). His skill level is add fuel check oil "where did it go in again?". I tried Break torquing in the driveway at2200 rpms for 15 min and all is good..Cruising at 2200 for 10 min and it will act up.The places where he consistently had problems there are several expansion joints in the road.The trigger apparently is warm engine with road vibration.Never acts up driving to work but almost everyday driving home now.Warm engine,multi tester,and a hammer may shed some light.These things are notorious for their flaky wire connections.Never seen a w-body without idiot lights twinkling like a Christmas tree for no reason.

Thanks all let you know if I find the source.

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To keep up to date on your threads..

 

click on your login ID at the top right of the forum page, a drop down menu will appear, select *My settings*, on the My Settings page from the left side sub menu select *Notifications Options*, on that page find Topics & Posts & turn on *auto follow topics* & select Immediate from the small tab choices. Turn on the *email* method of notification, now you will find emails in your mailbox every time a topic you're following is updated.

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Thanks for the step by step trucker.think they are on now.

Just got home,pulled the coils,checking all the connections again.Took the ICM out into the sun to get a  look at the pins again for corrosion.After closely scrutinizing the the pristine pins spotted cracks (1/8 inch melted lines) in the plastic by the coil posts on the passengers and center coils.Off to order a new ICM.This may not be the problem but definitely A problem.

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Few days of driving with the new icm and no problems so think that was it.The motor had a bit of shimmy to it at an idle since I got it 5 years ago.Now the motor sits rock solid in the bay at an idle and acceleration is much smoother than it has ever been.Throwing parts at a car to see what works is a pet peeve of mine.That's why I didn't replace the untestable ICM earlier. I have pulled that ICM out half dozen times since this started, looking for oxidation and cracks!Thanks for all the helpful advice.

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Few days of driving with the new icm and no problems so think that was it.The motor had a bit of shimmy to it at an idle since I got it 5 years ago.Now the motor sits rock solid in the bay at an idle and acceleration is much smoother than it has ever been.Throwing parts at a car to see what works is a pet peeve of mine.That's why I didn't replace the untestable ICM earlier. I have pulled that ICM out half dozen times since this started, looking for oxidation and cracks!Thanks for all the helpful advice.

Awesome! I'm glad my advice sending you here wasn't for nought! I would have completely missed that myself though, I despise parts swapping, I leave that for the Facebook guys who know nothing about cars. Lol

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I despise part swapping too, but sometimes it's the only thing that works. Especially if your choice is icm or cps, I know which one I'm going to try first lol. Glad you got it running again.

 

Testing while the issue is present can eliminate part swapping completely.

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Awesome! I'm glad my advice sending you here wasn't for nought! I would have completely missed that myself though, I despise parts swapping, I leave that for the Facebook guys who know nothing about cars. Lol

reminds of the kid at my local NAPA.Added 6 more cats to his car because "back pressure equals power!"LMAO

 

Testing while the issue is present can eliminate part swapping completely.

That was the problem.It would straiten up when I would start to test.Murphy and his laws are

 

It depends on the perspective. I personally don't mind doing a CKP or ICM because it's nice to know how old they are.

Did a "maintenance" swap IAC on fiero when I cleaned the throttle body.Replacement part died 1 month later,got a new one again,,,died 1 month later.Pulled the original off the shelf reinstalled and no more problems.Moral of the story is new is not always better.lol

 

 

 

 

Thanks again for all the input!

a pain!

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Not fixed,just less intermittent now.My son has been driving the car to work for the last weak with no problems.4 miles of highway and one mile city driving.I took the car yesterday to walmart.12 miles of highway driving.Ran fine driving out.Was in the store for 1/2 hour +/-. Car started up,sounded good.Made my way out of the parking lot down the road. the main road.first red light(1/4 mile) the idle sounded a little rough.Second red light (1/2 mile later) Sounded like The key was switched off for fraction of a second then back on.Pulled away from the light cruising at 45 it started to buck like it was running out of gas(has 3/4 tank) but had a gas smell so just not igniting it or too much gas.The bucking would last for a few seconds then stop. Next 2 red lights the car died but fire right back up. felt like it was flooded (fouling rich). The car started running consistently poor but I didn't have any tools to test it. Pulling away from the last light was feathering the gas and a neutral drop.I just stood on it WOT.It coughed sputtered then screamed up to 80.I slowed back to 40 back on WOT to 80.After that it drove the next 10 miles without missing a beat.Never has a service light.

 

I have too much gas or not enough spark causing plugs to foul.

 With the cold weather,electric fans may be adjusted too cold and my son driving like cautious little old lady,he may be closed loop all the way to work.Only acts up after reaching temp,parking and driving again.Temp was well under 210 when it acted up.

 

possibilities;

intermittent crank sensor causing foul

Bad ignition harness plug I haven't found to check

Fuel injector sticking open

fuel regulator sticking closed (full pressure)

fuel ratio may have messed up the cat but don't think the cat is messing up the fuel ratio

 

Anyone want to add or delete from my list??

I know this is long but "The more you know!"If you are old enough you saw that in rainbow font.

thanks all

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*never rains, but it pours*

 

If you suspect the FPR (assuming you have a hand held vacuum pump on hand) disconnect the vacuum tube from it & connect the pump & try to pull at least 15" of vacuum & *hold it continually*. 

If the vacuum holds then it's safe to say that the FPR diaphragm isn't torn & at fault (less vacuum more flow, higher vacuum less flow).

Trace back the vacuum tube to the map sensor to look for a leak in that tube.

Check the map sensor to ensure it is firmly fastened to the manifold & none of the ports are leaking.

 

The CPS is located in the center of the block on the backside just above the oilpan rail. Have a good look at the length of harness for insulation brittling, There should be a number of *twists* to that harness as well, if the sensor housing is covered with oil or if the housing has cracked & oil is leaking into the sensor that could cause an intermittent issue.

 

If it's possible the next time this happens can you limp the car home (without clearing the problem) & immediately pull out all of the plugs to look for any fouling?

If you don't find any then it's safe to say that flooding is not an issue. No flooding?.......possibly an injector driver harness issue, either on the fuse (voltage source) side of the injectors or the ECM side (control).

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FPR is not seeping fuel into vacuum line and holds 20psi for at least 15 minuets.I have never seen one stick but didn't know if anyone else had ever seen it happen. Tested the MAP with mutimeter and vac.All in rang.checked for vac leaks with propane but no fluctuation in rpm or tone.Replaced the MAP,FPR,PCV vacuum lines just to be sure.There is allot of road grime and oil on the CPS pigtail area.I guess that is the next in line.Thanks for the response.

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Just dawned on my when you are saying CPS you are referring to the crank position sensor not the cam position sensor,right?With my luck it is the one behind the pulley not under the steering pump.

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*Crank Position Sensor*........and there are two of them,

 

one is mounted to the backside of the engine block, this is the 3x sensor, just above the oil pan rail, this sensor has the *twisted* conductor (If memory serves it is 10 twists per foot) this is the primary sensor used by the ICM,

the second is the sensor behind the balancer, this one is the 24x sensor, it improves idle rpm quality & low speed driveability.  To get this sensor out one has to remove the crank balancer. 

 

My reference was to the 3x sensor.

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Usually, the 24x sensor won't kill the engine...and let's be honest, the 3X sensor is way easier to deal with.

 

Like Trucker said, back side of the engine block, just above the oil pan rail, passenger side.

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Glad I asked for clarification.Just looked at what I typed.I was still thinking of the cam sensor still when I was asking which crank sensor you were referring to.I thought the 24x "controlled" ignition from start to 2000RPM and the 3x took over for 2000 rpm and up.Bad 24x often no start and bad 3x cuts out when accelerating or holding higher rpms.Thinking back everyplace it acted up I had been accelerating or climbing a hill,cruising over 2000rpm.I always associate the 3x with hard acceleration but really anything but high idle would be 3x.....right? Have I got my brain wrapped the right direction around this now?

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