Vacuum Problem

[lince]

I have discovered that the problem with my car is that it isn't generating enough vacuum as it should and that is why it isnt working propriety and every time I press the gas pedal the engine tries to dies, anyone has an idea of where the problem of the vacuum can be coming from

[Vulcan Grey]

Mechanical pump is dead

vacuum lines to brake servo, heater controls, or rear relay panel are leaking.

[renckensj2]

I think that this problem is not caused by the mechanical vacuum pump since this pump is only involved in the engine performances when the engine is colder then 35

[lince]

I checked at every place on the engine with a vacuum exit an acording to the diagram of the car, and all of them show very little vacuum and went to 0 at very low RPM, I really haven

[Artie]

I checked at every place on the engine with a vacuum exit an acording to the diagram of the car, and all of them show very little vacuum and went to 0 at very low RPM, I really haven

[Vulcan Grey]

The pump can be replaced a NAPA #64-1006 will directly replace it for about $114.

If you have a disconnected line or cracked hose you won't be able to tell if the pump is working or not though. Directly connect the gauge to the pump while the car is running.

[Malc Holmes]

Hi guys,

I read this thread with interest since my SE has a similar issue. Throttle is cracked open and the engine dies a little before picking up. When the engine is totally cold this can cause it to stall.

I have always assumed its due to a leak in the manifold , allowing air in which results in a weak mixture at low engine speeds or false MAP sensor readings. This has been backed up by other postings on the subject. I don't understand how it can be related to the performance of the mechanical vacuum pump, which, other than feeding the throttle jack, dosn't seem to have any effect at low engine speeds as far as I can see.

Please explain!???

Thanks

Malc Holmes

[Vulcan Grey]

Hi guys,

I read this thread with interest since my SE has a similar issue. Throttle is cracked open and the engine dies a little before picking up. When the engine is totally cold this can cause it to stall.

I have always assumed its due to a leak in the manifold , allowing air in which results in a weak mixture at low engine speeds or false MAP sensor readings. This has been backed up by other postings on the subject. I don't understand how it can be related to the performance of the mechanical vacuum pump, which, other than feeding the throttle jack, dosn't seem to have any effect at low engine speeds as far as I can see.

Please explain!???

Thanks

Malc Holmes

Does your car start normally when warm?

If so then it sounds like you may need to check your IAC counts in freescan.

Using Freescan, start the car and let it reach operating temperature (water temp) of 82 deg. C.

Look at the IAC counts in Freescan. They should be between 20-40 while warm and idleing.

If not then your minimum air rate bleed screw on the throttle bodies (not the throttle butterfy balance adjuster) needs to be adjusted.

While still running slowly turn the flat head screw of the minimum air rate bleed screw (inside a protective aluminum cap) about 1/16 of a turn at a time while watching the IAC counts in freescan.

Get it to between 20-40 and make sure it stays for a while.

You stumbling, when you first touch the accelerator when the engine is cold, problem should be fixed.

If not then you may have an air leak. Make sure you fix all air leaks and then check the IAC counts when warm again.

[Malc Holmes]

Does your car start normally when warm?

If so then it sounds like you may need to check your IAC counts in freescan.

Using Freescan, start the car and let it reach operating temperature (water temp) of 82 deg. C.

Look at the IAC counts in Freescan. They should be between 20-40 while warm and idleing.

If not then your minimum air rate bleed screw on the throttle bodies (not the throttle butterfy balance adjuster) needs to be adjusted.

While still running slowly turn the flat head screw of the minimum air rate bleed screw (inside a protective aluminum cap) about 1/16 of a turn at a time while watching the IAC counts in freescan.

Get it to between 20-40 and make sure it stays for a while.

You stumbling, when you first touch the accelerator when the engine is cold, problem should be fixed.

If not then you may have an air leak. Make sure you fix all air leaks and then check the IAC counts when warm again.

Thanks Travis,

I'll check that out as soon as I can get the car back in my garage again (just finishing a reto in the brother in -laws Spitfire at the moment), its tucked away in someone elses garage at the moment. It would be great to get rid of the stumble since it has always taken the edge off the performance. The inlet system was new (from Gary Kemp) when I bought it and fitted it to my re-built engine. I would be supprised if the throttle bodies are out of ballence already, but it is cirtainly worth checking.

many thanks

Malc Holmes

[renckensj2]

As I explained already before, the vacuumpump is not involved in the engine management once the engine has reached a temperature higher then 35

[Malc Holmes]

As I explained already before, the vacuumpump is not involved in the engine management once the engine has reached a temperature higher then 35

[Vulcan Grey]

Yes, I can see where you are coming from, but remember we are talking about an SE (Delco injection) system here, i.e. no distributer, or advance capsule. All the advance is done elctronically using (I assume) engine speed inputs and the MAP sensor output to the ECU. I think you are refering to the Bosch injection system?

I personally think its down to a vacuum leak in the manifold or pipe to the MAP sensor, dodgy MAP sensor, or as Travis said, bad set up of the throttle body air bypass (come to think of it, my inlet system was for an S4s which may have needed different bypass settings than the SE). No probelms with brake effort, so I realy think the vacuum pump has nothing to do with the concern on my car at least.

Thanks

Malc

Lince has two problems most likely... One is his running stumble. the other is that he can't seem to measure any vacuum. Both need to be fixed. The vacuum might be just a case of not knowing where and how to diagnose yet (as he admits he doesn't know how).

I didn't say the vacuum pump or vacuum level would solve Linces problem, but if his system has a leak or isn't making vacuum it still has to be fixed as it is the booster for the brakes!

It's correct that the vacuum pump doesn't have anything to do with the running of the engine, other than the opening of the EBP Valve and the Throttle Jack.

Alejandro doesn't say whether the engine is dying while it is running or just ideling.

If it is ideling fine but stepping on the gas causes it to stumble and die (or any load on the engine causes it to die) then I would look at the MAP sensor, the igition coils plugs and wires, the throttle position sensor, or ECU. Also the IAC counts in Freescan as I mentioned above.

For Malc,

Since you said it only dies when you touch the gas when the car is still cold, I'm fairly sure it is the IAC attempting to adjust for a mis adjusted minimum air rate bleed screw.

DO NOT adjust the screw that sets the balance of the butterflies... I seriously doubt that has been altered, but the minimum air rate bleed screw is probably often monkeyed with by shade tree mechanics thinking they can adjust the idle by ear. You can't because the ECU will fight your efforts via the IAC.

[renckensj2]

Yes, I can see where you are coming from, but remember we are talking about an SE (Delco injection) system here, i.e. no distributer, or advance capsule. All the advance is done elctronically using (I assume) engine speed inputs and the MAP sensor output to the ECU. I think you are refering to the Bosch injection system?

I personally think its down to a vacuum leak in the manifold or pipe to the MAP sensor, dodgy MAP sensor, or as Travis said, bad set up of the throttle body air bypass (come to think of it, my inlet system was for an S4s which may have needed different bypass settings than the SE). No probelms with brake effort, so I realy think the vacuum pump has nothing to do with the concern on my car at least.

Thanks

Malc

Indeed, I was refering to the Bosch injection system and I see my mistake now. Sorry. One learns as long as one lives isn't it?

Regards

Jos

[lince]

My car is good at idle it just tend to dies when you try to accelerate, after a short time it starts picking up but no at the first time, even when the car is warm I have the some problem, I have tested the vacuum of the engine and the reading is very low and gets to 0 just after pressing the gas pedal. hope this gives you a better understanding of the problem, the map and baro sensor are fine i got them new a couple of months ago and they fixed another problem that I have and was cought with freescan

Lince has two problems most likely... One is his running stumble. the other is that he can't seem to measure any vacuum. Both need to be fixed. The vacuum might be just a case of not knowing where and how to diagnose yet (as he admits he doesn't know how).

I didn't say the vacuum pump or vacuum level would solve Linces problem, but if his system has a leak or isn't making vacuum it still has to be fixed as it is the booster for the brakes!

It's correct that the vacuum pump doesn't have anything to do with the running of the engine, other than the opening of the EBP Valve and the Throttle Jack.

Alejandro doesn't say whether the engine is dying while it is running or just ideling.

If it is ideling fine but stepping on the gas causes it to stumble and die (or any load on the engine causes it to die) then I would look at the MAP sensor, the igition coils plugs and wires, the throttle position sensor, or ECU. Also the IAC counts in Freescan as I mentioned above.

For Malc,

Since you said it only dies when you touch the gas when the car is still cold, I'm fairly sure it is the IAC attempting to adjust for a mis adjusted minimum air rate bleed screw.

DO NOT adjust the screw that sets the balance of the butterflies... I seriously doubt that has been altered, but the minimum air rate bleed screw is probably often monkeyed with by shade tree mechanics thinking they can adjust the idle by ear. You can't because the ECU will fight your efforts via the IAC.

[Paul93Lotus]

My car is good at idle it just tend to dies when you try to accelerate, after a short time it starts picking up but no at the first time, even when the car is warm I have the some problem, I have tested the vacuum of the engine and the reading is very low and gets to 0 just after pressing the gas pedal. hope this gives you a better understanding of the problem, the map and baro sensor are fine i got them new a couple of months ago and they fixed another problem that I have and was cought with freescan

Are your IAC counts in the correct range? That can cause several driveability issues as I experienced.

[lince]

Can someone confirm me if this is the right parts for a 1991 SE, I was yesterday checking and I would like to check every part of the brake system but wan

[Vulcan Grey]

Can someone confirm me if this is the right parts for a 1991 SE, I was yesterday checking and I would like to check every part of the brake system but wan

[ErnieHillard]

No, your 1991 SE probably has ABS brakes, so the master cylinder area is different. Not sure if the vacuum piping is the same though...

Do you have ABS?

Warmed up at idle how much vacuum should there be at the MAP and the fuel PSI regulator?

Ernie

[lince]

Yes I now the master cylinder is diferent but there is no other part of the manual showing the vacuum piping and that is what i would like to check, where they show the differences the just show the master cylinder but no connections