I have lurked on this site for awhile, researching the intake maniold problems. Our 95 Bonneville SE hydrolocked at 120k miles. Not knowing what happened we towed it to the local Pontiac dealer who replaced the intake manifold. That was over four years ago and about 45k miles. The last few months the car has been losing coolant, but it hasn't been running hot. I checked the dealer invoice and it looks like they may not have replaced the lower gasket, only the upper gasket was on the invoice.

Saturday I took the car for a TestCenter Only smog check on a dynamometer. And if failed badly and is now registered with the state as a gross polluter. The numbers were:
Test1 15 mph 1787 rpm 13.4 % CO2 2.1 % O2 9 HC (ppm) 0.00 % CO
3125 NO (ppm) (689 MAX, 1907 Gross Polluter)
Test2 25 mph 1901 rpm 13.3 % CO2 2.2 % O2 7 HC (ppm) 0.00 % CO
1827 NO (ppm) (706 MAX, 1707 Gross Polluter)
Everything passed the visual and functional tests, including the Oxygen sensor and the EGR valve.

The previous test was two years ago at the same test center and the results were:
Test1 15 mph 1796 rpm 15.1 % CO2 0.1% O2 15 HC (ppm) 0.01 % CO
70 NO (ppm) (689 MAX)
Test2 25 mph 1725 rpm 15.0 % CO2 0.1% O2 7 HC (ppm) 0.07 % CO
47 NO (ppm ) (706 max)

Obviously a lot more Oxygen and NOX in the exhaust, which from past posts could indicate EGR problems, I pulled the EGR valve and it wasn't stuck or plugged. The O2 sensor looks new, but I don't remember replacing it, I though it may have been the original, but it may have been replaced with the manifold work. Driving away from the test center the CEL came on and then went off a few minutes later. When the CEL comes on the engine surges above 2500 rpm, but only when warm. Plugs and filters were replaced before the test and the oil was changed.

Reading past post about cars with High NOX tests (none were this high that I found), the EGR seemed to be the main culprit, which is why i checked it and the connector. It wouldn't hurt to change the O2 sensor but it wouldn't seem to cause this problem. High NOX readings are supposed to be the result of high engine temperatures, the coolant gauge stays below the 200 mark, much lower than in the past. Is it possible I have another intake manifold failure? affecting the coolant temperature sensor by the IM? A bad CTS?

Friday I will have an Actron ScanTool CP9110 to read codes. Any wild ideas as to what can cause such high NOX values? On our 968 we had head gasket fail and suck out coolant slowly into the #4 cylinder. If a blown head gasket was the coolant loss culprit, couild it cause high NOX tests as well? Somehow I don't think there is a common source of coolant loss and high NOX values. Thoughts?
-sp4149

I can't begin to comment on your data, but the gearguys will have questions and directions to go.

On the Actron CP9110, be sure you're getting the CP9115 cable that you need along with it to fit your '95. Many times it'* not included and you only get the one for '93s and earlier. Get back to us if it'* not there and not available.

Welcome to the club .

Your high NOX and low CO and HC indicate the possibility of a lean A/F ratio...possibly a massive (and maybe intermittent) vacuum leak. The quickest thing to check would be the PCV cap and the o-rings under it. If that looks OK, do the standard check of all the vacuum lines and intake/TB gasket sealing surfaces with short sprays of carb cleaner with the engine running (listen for a stumble, indicating the carb cleaner was sucked into a leak in the vac system or an unsealed gasket).

On the Actron CP9110, be sure you're getting the CP9115 cable that you need along with it to fit your '95. Many times it'* not included and you only get the one for '93s and earlier. Get back to us if it'* not there and not available.

What are the connectros needed to adapt an OBDII cable? There are enough electronics/computer stores here that i should be able to clone something if I know the pin connections and get the right connectors.

-sp4149

The Vacuum hose to the firewall for the HVAC distribution system was broken clear through at the firewall. Would that have been enough to trigger such high NOx levels?

-sp4149

That would certainly fall into the category of "massive vacuum leak."

How long have you been running this way? Have you had issues with your HVAC system?
(I ask because this might trigger an "oh, yeah, three months ago my vents started acting up...")

You've likely been running very lean and experiencing high knock.
You say you changed your plugs just before the smog test--please tell me you saved your old plugs for examination...

This is Bill Buttermore'* schematic for the hook-up to '94-'95 Bonnevilles:

http://www.bonnevilleclub.com/forum/...ic.php?t=40310

You would need to find a J1962 male plug for your underdash socket, and a female DB15 socket. Use 24 gauge wire or bigger.

I still have enough parts left to make you one at cost (I've made a couple for club members). PM me if you're interested.

The mid-level dash vents shut down the week before the test. Some flow out of the defroster vents and some out of the floor, but nothing out of the middle. Following the service manual I identified one of the three doors as non-functional and was going to investigate further after the smog test. The 7/32nd hose looks new except at the fitting by the firewall. The hose end was soft and puffy and probably failed soon after I moved it around when changing the spark plugs (big hands, hoses get in the way back there). I had already determined the vent doors were vacuum actuated so knew this would fix the A/C problem. I still am getting the on again off again CEL So there is probably something else in need, maybe a sensor.

Yes I saved the plugs and labled them by cylinder. I even have a previous set. They all had widened gaps, around .075+" from the initial .060". All tips were gray-tan without buildup. The threads of four looked oily (1,2,3,5), while on two (4,6) the bottom threads by the tip were dry and burnt rust looking. I was thinking that these might have been from cylinders where the bead gaske was leaking coolant.
-sp4149

First off, it sounds like the accesory vac line has only been a problem for a week or two...that'* good, not alot of time to do damage.
Hopefully there are no flakes of piston metal stuck to your old plugs.

Second, you say the CEL keeps coming on...is this after you have fixed the vac line?
More importantly, assuming you have fixed the vac line, are you still having surging / driveability problems?
(It is possible the CEL is just "set" even if the problem has been fixed, and simply needs "x" number of on-off cycles or the scantool to clear it)

Third, which gaskets did you have replaced a few years ago, upper or lower? (or both?)
Either way, 45k is certainly enough miles for a new set of plastic lowers (or the UIM) to re-disintegrate.
Your plugs (4 and 6 "rusty-looking") suggest a re-disintegrated lower intake manifold gasket on the rear bank.
Does your exhaust smell "sweet"? At what rate are you losing coolant?

It is certainly possible that you need another LIM gasket job. I'm eagerly awaiting the results of your scantool reading.

P.*., whereabouts in San Diego are you?

First off, it sounds like the accesory vac line has only been a problem for a week or two...that'* good, not alot of time to do damage.
Hopefully there are no flakes of piston metal stuck to your old plugs.

Second, you say the CEL keeps coming on...is this after you have fixed the vac line?
More importantly, assuming you have fixed the vac line, are you still having surging / driveability problems?
(It is possible the CEL is just "set" even if the problem has been fixed, and simply needs "x" number of on-off cycles or the scantool to clear it)

Third, which gaskets did you have replaced a few years ago, upper or lower? (or both?)
Either way, 45k is certainly enough miles for a new set of plastic lowers (or the UIM) to re-disintegrate.
Your plugs (4 and 6 "rusty-looking") suggest a re-disintegrated lower intake manifold gasket on the rear bank.
Does your exhaust smell "sweet"? At what rate are you losing coolant?

It is certainly possible that you need another LIM gasket job. I'm eagerly awaiting the results of your scantool reading.

P.*., whereabouts in San Diego are you?[/quote]

First, as I said I may have broken the deteriorated vacuum line when I was changing the rear plugs. as you said a very recent event.

Second, the CEL continues to come on after a few minutes then is going out when hot. I am only driving the car on shorter trips 10-15 minutes and not using it for commuting. Since fixing the vacuum line the surging seems reduced but i haven't driven the car in the same situations, normal operating temperature on the freeway. It seems that a bad coolant temperature sensor (mounted under the thermostat) can cause some problems as well . It seems the dash temp gauge is reading lower than before although the NOX emissions would indicate an engine running hot; this has been going on for a few months now.

Third, the dealer invoice only listed an upper gasket, although the Service Bulletin i found later recommended upper and lower. Since #6 is next to the EGR, the root of the UIM problems and the lower gasket may be original; your idea about the lower gasket failing seems likely. No sweet smell or hot coolant smell like I noticed on the 968 when it'* head gasket was failing and no clouds of steam yet when starting like when the 968s gasket finally went. I would say coolant loss has been about a quart every 400-500 miles, although in the last 200 miles it probably hasn't been more than 1/2 pint.

I used to work at the Navy Broadway complex which will probably be another redevelopment boondoggle/disaster. I'm now at the32nd street complex, closer to home in Chula Vista.

-sp4149