2000 SL2 DOHC vacuum line question

[302MGB]

New guy here. I'm helping someone fix a P0300 code. On initial inspection, I found a vacuum port on/near the number 1 cylinder intake runner with no vacuum line on it creating a notable vac leak. I couldn't find a loose hose so for the moment, I simply capped the port. Can someone let me know where that vacuum port is supposed to connect? Maybe provide a picture highlighting it? Thanks in advance!

[302MGB]

No one?

[leighv]

is that the hard plastic line that nests in the crease of the valve from front to back? i believe thats something for the secondary air injection. (pushes air into exhaust to heat up the catalytic converter)

[302MGB]

Could be and that could explain them saying it was making noise until it warmed up. Is the air pump thermostically controlled?

At the same time, it doesn't seem likely. The open port was definitely a vacuum port and I believe it was plastic. I can't imagine where vacuum would be coming from on an exhaust? And, assuming my memory (wish I'd have taken a picture) is right and it is a plastic nipple, I can't see that being on exhaust either. Since capping that vacuum port (and clearing the code -P0300 - missfire on multiple cylinders), the code has not returned. It's only been driven about 25-30 miles, but they said when someone cleared the code before, it came back within a mile. The open vacuum would explain misfires.

So, I'm not sure we're talking about the same thing?
The link you shared isn't working but I'll use RockAuto or google to figure out what the air injection pump looks like so I can see if its hooked up.

The person I'm helping is out of town for work (they got their employer to pay for a rental) so it'll be a few days or the weekend before I have an update.

[leighv]

It's been quite a few years since i have removed the secondary air injection. but alas here is the factory service manual diagram illustrating the line in question.
Here is the description, straight up copy/pasta'd. Merry christmas

"
The AIR system is used to reduce hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOX) exhaust emissions by heating up the catalytic converters quicker on cold engine start-up. The conversion of exhaust emissions to carbon dioxide (CO2) and water can occur sooner as the catalytic converter reach the normal operating temperature around 527°C (981°F). The AIR system consists of:

Air pump (1)
Check valve (2)
Air pump solenoid (3)
Combination valve (4)
Air pipe and hose (5)
Vacuum hose (6)
Air pump relay - located in underhood fuse block (UHFB). (7)
Powertrain control module (PCM) - located underhood between the battery and power brake booster. (
The air pump is a permanently lubricated turbine type pump which requires no periodic maintenance. The PCM runs the air pump for a certain length of time when the engine is started within a certain ECT range. When the air pump is commanded ON, the PCM will command an internal driver ON which pulls the air pump relay circuit to ground allowing current to flow to the air pump.

The air pump solenoid is used to control vacuum to the combination valve. When the air pump relay is commanded ON, air pump running), the PCM will wait a short amount of time to command the air pump solenoid ON. The PCM turns the solenoid ON by controlling an internal driver that pulls the solenoid circuit to ground. The PCM waits to turn the solenoid ON in order for the air pump to pressurize which keeps exhaust gas from entering the air pump.

When the air pump and air pump solenoid are turned ON, vacuum to the combination valve will allow the spring loaded diaphragm, upper valve in the combination valve, to be pulled up. This will allow pressurized air from the air pump to flow around the reed valve, lower valve in combination valve, to the exhaust manifold.

Before the PCM commands the air pump relay OFF, it will first command the air pump solenoid OFF and wait a short amount of time before it commands the relay OFF. This keeps exhaust gas from entering the air pump.

Air System Enable Criteria
The traction control is not active.
The battery voltage is between 11-18 volts.
The ECT is between 4-79°C (40-174°F).
The IAT is greater than 0°C (32°F).
The engine speed is less than 3,200 RPM.
The MAP is greater than 20 kPa.
The calculated engine airflow is less than 30 g/s.

"

[302MGB]

Christmas indeed!! Thank you leighv; that definitely explains how a vacuum source is involved in the air injection system. I generally work on vehicles that pre-date most emissions systems (and ECU's for that matter); the only similar system I've seen was on later MGB's which had a very simple air pump design by comparison.

I should be able to have another look at the car in the next day or two to confirm. The good news is it's been driven about 200 miles and the CEL has not returned.

Question, the owner needs to get the vehicle inspected. In TX the safety inspection includes a tailpipe O2 sniffer test. Based on the above, it would seem that not having the air injection should not affect emissions readings since they do the test with the vehicle warmed up so cat is functional. Agree?

[leighv]

I concur
best of luck to car and owner... The cars are becoming scarce these days.

[302MGB]

Looked at the car again today. For the life of me, I couldn't find the air pump or the solenoid. I suppose it could have been removed before the current owner bought the car. They didnt recall having it removed. Here are some engine bay pics. If you see it or can point me to where it should be, please let me know. Based on the diagram above, looked all around the compressor, the core support, etc. I did see what must be the water pump under the compressor (although different in design than I'm used to). I didn't see anything that looked like it had an air injection hose going to the head or exhaust. Bit, I also didn't see any brackets or other spots where the pump might have been before so not sure.

The owner is a young lady in a Bible study my wife and I lead for College & Young working singles. She's probably going to replace the car as it has 215k miles and is burning a LOT of oil (I filled it when she was here last weekend; it was about 1.75 quarts low and It's burned about 3/4 quarts in the ~250 miles this week (there's a slight leak, but nothing that accounts for that much).

But, I'd still like to know if I'm just missing where the pump and solenoid are so if you see them, please let me know.

IMG_20230212_165627335_HDR.jpg

IMG_20230212_165632862.jpg

IMG_20230212_165704354.jpg

[leighv]

That exhaust manifold indicates you do not have a pre-cat integral to said manifold. you have no air pump etc. this is possible in this model year. (2001 -2002 i believe most or all had air pumps).



interesting to see the AC clutch pulley completely missing.

These cars burned oil if the oil was not changed very regularly. A decade ago most of these cars could be recovered if ran a full synthetic oil, and the oil control rings were decoked (seafoam treatment etc) sufficiently such that they were not seized in the piston groove. This generation engine also had ultra-thin piston crown to the top compression ring distance (note the longer connecting rod length vs 91-98 years). the hyper eutectic pistons can and will crack. Other than that clean the shit out of the PCV valve. you could try a 5w or 0w -40 oil to decrease consumption.

The water pump is indeed below the AC compressor on the front of the engine. fairly easy to change if needed.

Check the gas, add oil.

in 2009 -2010 my family had several cars we ran and managed with minimal oil consumption. But alas you have a hard -run survivor i reckon.

[302MGB]

Excellent Info; thanks again!