98 Pontica Bonneville: Any know pattern failures

jay

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Sister in law planning to bring her 98 Bonneville over Sat. Has 125,000 miles. Complaint is rough idle. Also has CEL on.

Any known things to check out on this 3800 engine? Does it have problems with lieaking plastic intake plenum?

I'll check the MAF, EGR, and codes with scanner and post back later with findings.
 

Gus

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She the original owner? If no, plenum may have already been replaced....if losing coolant and and NO VISIBLE EXTERNAL LEAKS, then it's a possibility...if there are external leaks, do a pressure test to find them all....

Car ever been tuned? Could be a misfire......if orig wires, pull wires off coil terminals to look for corrosion.....check coil output, and do complete tuneup with OEM parts, if necessary...
 

jay

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She is orginal owner. Unknown at this point about any replacement of upper intake or maint history. Does the 3800 have similair problem with leaking lower intake manifold gasket like the 3.1? I' fairly knowledgeable with the 3.1. Thanks, jay
 

Gus

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No, they are two different beasts...the problem is usually the upper plenum, not the lower intake....
 

jay

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Thanks for info Gus. I'll look at it over the weekend...if she bothers to bring it by. She said she had taken it to dealer months ago but they could not get the"light" to stay turned off...? LOL. Guess they weren't too up to date on OBD2 since it has only been out since around '95 on some cars...LOL.
I expect it to be in need to basic tune up, etc based on past history with her cars.
 

Mikerizer

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I would HIGHLY recommend checking out that upper intake plenum. I had a '98 Olds 88 with the 3.8L, and the plenum failed at about 85K miles. She's driving on borrowed time, in my opinion.
 

jay

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Mikerizer said:
I would HIGHLY recommend checking out that upper intake plenum. I had a '98 Olds 88 with the 3.8L, and the plenum failed at about 85K miles. She's driving on borrowed time, in my opinion.
If upper intake is bad, is it due to gasket under plenum or warpage of entire Plenum? If replacement plenum is needed; does OEM part have better part than aftermarket for this type of repair? I use mostly OEM parts during repairs but have found some FELPRO gaskets are designed to address some problem areas in such engines as lower intake manifold leaks in 3.1s.
thanks, jay
 

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This is not the gasket that leaks, it's the intake plenum itself. It burns a small hole in the EGR passage that leaks coolant into the engine and usually into the oil or combustion chamber. Either place it goes spells certain death for the engine. Dorman makes an updated redesigned plenum with aluminum passage that won't burn through like the OEM will. You can usually get that brand at Auto Zone or most parts stores. Tell her not to take chances, get it checked ASAP if not sooner. Thats an expensive engine to rebuild!
 

jay

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sunny said:
This is not the gasket that leaks, it's the intake plenum itself. It burns a small hole in the EGR passage that leaks coolant into the engine and usually into the oil or combustion chamber. Either place it goes spells certain death for the engine. Dorman makes an updated redesigned plenum with aluminum passage that won't burn through like the OEM will. You can usually get that brand at Auto Zone or most parts stores. Tell her not to take chances, get it checked ASAP if not sooner. Thats an expensive engine to rebuild!
Thanks for the info Sunny. I knew that Dorman/Mortormite made a replacement plenum, just was not sure it aftermarket was the way to go on this or OEM. I'll have the car tomorrow and check it out closely.
 

jay

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She brought the car to the house Sat and here is what I found:

It has 140,000 miles, 3.8, VIN K. 1998 Bonneville SE

MIL commanded on by P0135 (O2 B1S1 heater circuit)
also had P0300B Random mutiple misfire.

I let it cool down and looked at the misfire counters real time with my Genisys. I could see cyl 2 misfiring slightly at idle. Under misfire history, cyl 1 had 26,#2 had 40,863, #3 had 87, #4 had 3, #5 had 30735, #6 had 87. Noticed Cyl 2&5 use same coil but did not have time to swap around with other coils to see if misfire tracked to coil.

For the P0135, I saw that it took 120sec for heater to warm up, spec max is 60 sec. It took a noticeably long time to go into close loop.

One item of confusion, there is only one upstream 02 on this car, it is on rear banK (Bank 2). Wonder why code set for Bank1 one Sensor 1, looks like it should have been B2 Sensor 1 since #1 cyl is on front of engine. Need clarification on this. Have alldata for this car and it only shows the upstream on B2. Car has exhaust crossover pipe form Bank 1 exhaust.

Coolant in overflow take is Dexcool and very clean without sludge or oil. Someone wrote "12/14/04, -34F" on the tank, so it must have had some recent service. Engine plastic cover is still in place; looking at the side next to EGR looks like it has been replaced.

She's bringing it back Friday and leaving it overnight. I plan to replace plugs, wires, and upstream O2. Will check out coil afterwards for misfires to see if a problem anymore. I'll do a coolant pressure test also. Will also clean MAF

Anything else I should check out on this? Thanks, jay
 

Gus

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Like the guys said, for piece of mind, take the upper plenum off, and check the hole where the EGR tube goes through, for degradation of plastic in the hole....if ok, just replace the plenum and throttle body gaskets..

I would change the thermostat and also the plastic elbow that comes out of the lower intake and goes into the tensioner assembly on the passenger side.....the end of the elbow has been known to break inside the intake and cause a leak....you have to pull the tensioner assembly out......replace the O-ring that attaches it to the block....

Does sound like a 5/2 coil problem...any corrosion on the terminals when you pulled the wires off it?
 

jay

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Gus said:
Like the guys said, for piece of mind, take the upper plenum off, and check the hole where the EGR tube goes through, for degradation of plastic in the hole....if ok, just replace the plenum and throttle body gaskets..

I would change the thermostat and also the plastic elbow that comes out of the lower intake and goes into the tensioner assembly on the passenger side.....the end of the elbow has been known to break inside the intake and cause a leak....you have to pull the tensioner assembly out......replace the O-ring that attaches it to the block....

Does sound like a 5/2 coil problem...any corrosion on the terminals when you pulled the wires off it?
I didn't get a chance to look at the coils. She's bringing it back Sat. I'll check out the plenum closely then. Thanks, jay
 

jay

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jay said:
She brought the car to the house Sat and here is what I found:

It has 140,000 miles, 3.8, VIN K. 1998 Bonneville SE

MIL commanded on by P0135 (O2 B1S1 heater circuit)
also had P0300B Random mutiple misfire.

I let it cool down and looked at the misfire counters real time with my Genisys. I could see cyl 2 misfiring slightly at idle. Under misfire history, cyl 1 had 26,#2 had 40,863, #3 had 87, #4 had 3, #5 had 30735, #6 had 87. Noticed Cyl 2&5 use same coil but did not have time to swap around with other coils to see if misfire tracked to coil.

For the P0135, I saw that it took 120sec for heater to warm up, spec max is 60 sec. It took a noticeably long time to go into close loop.

One item of confusion, there is only one upstream 02 on this car, it is on rear banK (Bank 2). Wonder why code set for Bank1 one Sensor 1, looks like it should have been B2 Sensor 1 since #1 cyl is on front of engine. Need clarification on this. Have alldata for this car and it only shows the upstream on B2. Car has exhaust crossover pipe form Bank 1 exhaust.

Coolant in overflow take is Dexcool and very clean without sludge or oil. Someone wrote "12/14/04, -34F" on the tank, so it must have had some recent service. Engine plastic cover is still in place; looking at the side next to EGR looks like it has been replaced.

She's bringing it back Friday and leaving it overnight. I plan to replace plugs, wires, and upstream O2. Will check out coil afterwards for misfires to see if a problem anymore. I'll do a coolant pressure test also. Will also clean MAF

Anything else I should check out on this? Thanks, jay
Ok, heres an update.
I replaced the upstream O2 and the front 3 plugs. I also swapped coil 2&5 with 6&3 locations to see if high misfires on coil 2/5 was indication of coil going south.
Cranked up and immediately head a spark to ground sound coming from coil areas. Checked and found boot on #5 coil would not click on terminal. I squeezed the inner terminals tight with pliers and snapped it in place. Also pulled all coil terminals and found rusty color under #4 coil and discovered it was not snapped in placed. Tightened the terminal up with pliers and put on.
Cranked car and it now idles smoothly; after going in close loop, viewed O2 and saw it switching from .8 to about .2 with good crosscounts.
Took car on test drive. During Full throttle acceleration to get on interstate, MIL came on. Took car back home and found P0300B multiple misfire codes. Freeze frame showed 100% throttle opening at 67mph, open loop. I assume it was open loop due to WOT.
STFT at idle is +2%, LTFT is 0. Misfire history: cyl 1: 2, cyl 2: 538, cyl 3:1, cyl 4: 0, cyl 5: 281, cyl 6: 0.

The plugs I replaced at 1,3,5 had normal ash color and were AC 41-921 (probably orginal plugs since the replacement plug is 41-101. Plug gap on old plugs was greater that .060. Can I assume that they would be clean if coolant was getting onto them from leaking intake?

This Wed, Im going to replace all plugs and wires (AC Delco wires.) Plan to do a snap throttle test to check out MAF. Also will check fuel pressure.

Anything you suspect on this problem? Im wondering if this misfire if fuel pressure related. Will also check fuel pressure. Looking at the plastic intake manifold, it had the following part number sticker: Delphi E 52727204314 I. Is there anyway to check to see if this is a replacement for earlier defective manifold? I checked around the manifold under EGR and did not see any damage from EGR heat. I pressure checked coolant system and it had very slight drop after 5 min.
This car saw regular service at GM dealership, I'm wondering if they replaced the uppler intake at some time?

Thanks for any help.
 

jay

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Fixed:Re: 98 Pontica Bonneville: Any know pattern failures

fixed

I replaced all the plug wires today and pugs. Used AC Delco spec parts.
After about 20 min of driving at various speeds, included interstate, no MiL light.
Hooked up scanner, no pending codes; also all cylinders display "0" in misfire history.
Sis in law says it runs great.

Thanks for all who provided info to get this fixed. I told her to keep an eye on coolant level and oil for possible intake leak.
 
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