1800 Cars: Manifold Absolute Pressure (MAP) sensor repairer?

[Derek UK]

I'll preface this by saying that I know nothing about this unit or how it really works. Is it basically redundant after start and a sensible warm up period. How much work does it do +/- during normal running? Would it work acceptably well feeding a fixed but average signal to the ECU?
I'm thinking of a switched type potentiometer which has resistors controlling the output at each switched step. These are used for volume controls on hi fi. By altering the resistors you could create an output curve that suits, say starting/cruising/sporty driving. Yes it would be manual but as a cheap compromise it might work. Experimentation would take time but resistors are cheap and so are these type of pots if bought from China. They are pretty well all made there anyway.
If I'm talking rubbish I will not be unhappy if I'm told that!!

[packers1712]

Hi I realise I’m jumping in a decent way through this thread but I have had a decent amount to do with these owning a VW Type 3 with D Jet, it is not possible to swap this sensor for anything else there are way too many variables that it controls and it is a highly tuned piece of kit specific to your car only which is set up at Bosch for each manufacturer depending on engine size all the way to where the car was destined for in the world (external atmospheric considerations), I’ve been to this movie! I have a good one of these that I bought from Canada last year unfortunately it is a 007 not a 010 number at the end of the part number rendering it no good for your car. When your checking the vacuum make sure you have a good seal around the pipe inlet as that can be a cause of rapid leaks!
Good luck finding a replacement I found them to be like the proverbial rocking horse sh@t and good ones are fetching big money. Make sure if you are going to buy a second hand one (as opposed to NOS) that the tamper bung in the end is still present if not it will have been adjusted and without the proper knowledge of these can make the car they’re fitted to run terribly!

Doug.

[142 Guy]

Originally Posted by Derek UK

I'll preface this by saying that I know nothing about this unit or how it really works. Is it basically redundant after start and a sensible warm up period. How much work does it do +/- during normal running? Would it work acceptably well feeding a fixed but average signal to the ECU?
I'm thinking of a switched type potentiometer which has resistors controlling the output at each switched step. These are used for volume controls on hi fi. By altering the resistors you could create an output curve that suits, say starting/cruising/sporty driving. Yes it would be manual but as a cheap compromise it might work. Experimentation would take time but resistors are cheap and so are these type of pots if bought from China. They are pretty well all made there anyway.
If I'm talking rubbish I will not be unhappy if I'm told that!!

Definitely not redundant after start. It is the electrical equivalent of the venturi and metering jets in a carburetor and is the primary sensor that determines how much fuel should be delivered for each engine cycle.

Unfortunately, a variable resistance as a substitute for the signal on the output winding of the sensor will not work. That would be an easy fix if it did.

[142 Guy]

Originally Posted by packers1712

When your checking the vacuum make sure you have a good seal around the pipe inlet as that can be a cause of rapid leaks!

I was about to apply a similar bit of advice to make sure that it is not the internal seals in the hand vacuum pump that are allowing leak down. Wouldn't be the first time that the test equipment gave erroneous results.

[ChasesDragons]

Thank you Doug, Derek and c1800. That is info that will narrow my search. It is becoming increasingly apparent that a different engine management system is worth exploring.

142, again, you have left me standing in the dust with your knowledge!! 👀💫

Kurt has been very kind and helpful over on the Facebook P1800 groups. There are two issues with getting it from him - I am on the other side of the pond and her Majesty will screw me with about 40% of all the associated costs of getting it here, then I have to get it further tuned here. I did not even think of the third problem of cold running. He has moved to.Florida nowadays, which doesn't exactly suffer our weather either.

I have found British sources who work with MS and I will take advice from them re any of the other management systems that might be relevant and established here. Thanks also to the reference for the Brit tuner.

The vacuum seal was checked - it is on a freshly brightened nipple. The Vacuum held on two of the W114 MAP sensors so its own integrity is trustworthy.

C1800, you are echoing concerns by other people that I have spoken to, that there will be borewash and petrol everywhere from my attempts. The fresh oil now stinks of petrol (opening the rocker cover to set TDC), I dread to think of the brand new spark plugs condition.

Question now is gentlemen- how big is the jump from an inevitable MAP sensor and loom buy to a new Engine Manahement system......

[142 Guy]

If you pay somebody else to build it, install it with a custom wiring harness and then do the software configuration and tuning you will be way beyond the cost of a MAP sensor rebuild by Bosch or a rebuilt sensor from Scandcar or Iroll. I suspect that you would be in the same cost range as if you purchased an engine, transmission, engine wiring harness and ECU from a wrecked 10 year old Mazda MX5 and transplanted it into the 1800 (that is based on wrecker costs in North America).

If you are prepared to wade into the Megasquirt manuals (or the application guides for whatever system you might purchase) then the costs become more reasonable. I acquired a lot of my parts from a local pick and pull salvage yard and I repurposed the orignal D jet harness. Total cost of my system is probably in the $700 - $1000 Cdn range which includes a spare controller; but, is based upon MS2 prices from about 7 years ago. Still more expensive than a rebuilt Bosch MAP sensor and its going to take a while before you can get the car to the point that you can drive it.

I would be inclined to re assess the condition of the D jet system. If it is just the MAP sensor that is faulty, I personally would be inclined to consider the purchase of a rebuilt MAP sensor rather than launching on a conversion to digital EFI unless you want a project that is going to take you well past the end of the COVID 19 lock down (I hope).

[Clan]

Originally Posted by ChasesDragons

Thank you Doug, Derek and c1800. That is info that will narrow my search. It is becoming increasingly apparent that a different engine management system is worth exploring.

142, again, you have left me standing in the dust with your knowledge!! 👀💫

Kurt has been very kind and helpful over on the Facebook P1800 groups. There are two issues with getting it from him - I am on the other side of the pond and her Majesty will screw me with about 40% of all the associated costs of getting it here, then I have to get it further tuned here. I did not even think of the third problem of cold running. He has moved to.Florida nowadays, which doesn't exactly suffer our weather either.

I have found British sources who work with MS and I will take advice from them re any of the other management systems that might be relevant and established here. Thanks also to the reference for the Brit tuner.

The vacuum seal was checked - it is on a freshly brightened nipple. The Vacuum held on two of the W114 MAP sensors so its own integrity is trustworthy.

C1800, you are echoing concerns by other people that I have spoken to, that there will be borewash and petrol everywhere from my attempts. The fresh oil now stinks of petrol (opening the rocker cover to set TDC), I dread to think of the brand new spark plugs condition.

Question now is gentlemen- how big is the jump from an inevitable MAP sensor and loom buy to a new Engine Manahement system......

Have you thought about putting the FI system from a late 940 on it ? it should be very close and run like a dream ..It would need a lambda sensor of course

Talking of bore wash , when the 144GL and 1800E were new they came in from the transporter stinking of fuel , there were a couple of pints of fuel in the sump due to all the cold starts in between the factory and dealer ..

[Burdekin]

The jump to mega squirt for FI and ignition on a P1800E would be good, it’s a excellent system. If you can’t do it yourself then it’s finding someone competent to do the work for you at a reasonable cost. Worth contacting the folks selling mega squirt and enquiring about how much to install and who can do it for you.

[Burdekin]

Couple of companies to enquire about a conversion and costs: http://www.extraefi.co.uk/services.html

[ChasesDragons]

My concern is what else is lining up to blow up in the 50 year old system. If I go for a rebuilt MAP.......

Originally, I was going to have someone rip out the engine and install a T4 engine which we thought might just fit in. I think I would like to keep it near as a P1800E megasquirt being the farthest departure.

Originally Posted by 142 Guy

SNIPPED.

I would be inclined to re assess the condition of the D jet system. If it is just the MAP sensor that is faulty, I personally would be inclined to consider the purchase of a rebuilt MAP sensor rather than launching on a conversion to digital EFI unless you want a project that is going to take you well past the end of the COVID 19 lock down (I hope).