Degree in Digijet technology!

[Mr Bean]

Do I need one? Desperatrely waiting for the rain to stop and the weather to warm up so I can induce my "Vanagon Syndrome" and substitute the ECU I decided to try to understand the mapping on the intake air sensor. I expected to see some kind of curve equating to an increase in flow but instead saw some incomprehensable variations. Looking at the ceramic panel which comprised the curved track and fired on circuit I have difficulty working out the designers intent. Another thing which baffled me is the little wire leading into a plastic block gissmo which seems to work in parallel with the berrilium copper spring contacts. While this does work in the non-fault condition I would still like to know what it does exactly and how it could cause my fault if indeed it was the culprit. So my question is:
Does anyone have the figures for the resistance versus angle?
Does anyone know what the little wire and plastic block does?
I don't suppose anyone has an air intake sensor and an auxiliary air regulator with which I could complete my set of replacement parts for the ignition and fuel injecion system?
Before anyone pipes up I know this behaveour seems obsessive but I am driven to get to the bottom of this problem.
Obsessive Ken
By the way we are talking about a 1988 2.1 digijet waterboxer.

[Grun]

Ken,

Mr. Haynes says...........

Between terminals 3 and 4 resistance should be between 500 and 1000 ohms

Between terminals 2 and 3 the resistance should vary as the airflow meter flap is moved back and forth.

Between terminals 1 and 4 the resistance should correspond to that given in the specifications for the intake air temperature sensor.

Air intake temperature sensor specs.

At 0 degrees Celsius 5500 ohms approximately
At 20.........................2500
at 45.........................1000

Mike

[Mr Bean]

Ken,

Mr. Haynes says...........

Between terminals 3 and 4 resistance should be between 500 and 1000 ohms

Between terminals 2 and 3 the resistance should vary as the airflow meter flap is moved back and forth.

Sorry Mike I should have been more specific. It does meet the Haynes spec which is also in the more comprehensive manual by Bentley Publications. I meant the relationship between amount the flap opens in degrees and the resistance value at each position say in 5 degree steps.
Thanks anyway
Ken
(Give me cough and splutter any day in preference to this sudden dumb insolence and refusal to run malarky. At least you can limp home.)

[ermie571]

sorry - can't haelp with the technical stuff, but this bit

sudden dumb insolence

made be laugh lots.....


sounds like the van is growing up....and has hit mid-teens! Buy it an ipod, and grunt at it, don't expect ANYTHING before 10am and you should be ok!!!

hehe

sorry - technical assistance can now be resumed!

Em
x

[Grun]

My fault Ken should have read through more carefully.

I am a bit handicapped with cataracts at present, not driving as a result, and the van is in my garage loaded up so not able to open engine cover or even get right round it.

Chuck the lot out and fit some decent carbs and a set of points (sez Oi!!)

Mike

[jamesc76]

if you think its the ecu and you seem to know what your talking about why not try the Megasquirt self build ecu ??? Ibuilt one a while ago for a mate the instructions are easy to follow!

[syncrosimon]

The best technical advice I have seen on our injection systems has come from the States. They seem equally perplexed by the irregularities and obscure faults that VW installed from new. I will have a dig around and see what I can find. I think that the problem lies in all the associated idle stabilisation that was needed to keep the engines running smoothly at tickover. This system is a bit of a bolt on to an existing ECU meant for an inline 4. I think there lies the problem, however, when they do run, they run very well.

I think that if you get to a stage where you fully understand this system, you will be the first.

[syncrosimon]

if you think its the ecu and you seem to know what your talking about why not try the Megasquirt self build ecu ??? Ibuilt one a while ago for a mate the instructions are easy to follow!

Now that is a bloody brilliant idea.

[Mr Bean]

if you think its the ecu and you seem to know what your talking about why not try the Megasquirt self build ecu ??? Ibuilt one a while ago for a mate the instructions are easy to follow!

Now that is a bloody brilliant idea.

Yes that idea appeals at first sight but being an ex "aerospace" production engineer and a very intuitive hands on maker of things to work and although equipped with some kit ranging from lathe & mill through to oscilloscopes and the like, I am sick to death with little black boxes and circuit panels which are designed by Tefal extended forehead types and only vaguelly understood by the silly sods who managed to cobble them together for production. I have a substitute ECU now and if that doesn't do the trick I have to consider stuff like the Intake Air sensor and Auxiliary air regulator. While the T25 is in my opinion built like a brick toilet block I do find this early engine management system very vulnerable in terms of diagnostics and parts availability. I am begining to wonder what a carb conversion would cost and whether I could use my new Dizzy and Ignition module with it. I have booked another recovery for later on today so if anyone sees a blue and white hightop repeatedly thrashing between junctions 7 & 8 and posibly broken down in the most embaressing place give me a wave!
Cheers
Ken

[HarryMann]

Didn't ask the other day, but have you set/reset/checked the throttle idle cut-off setting? That's often said to be soemthing needing setting-up accurately before anything else.

You appear to working down the line of thought that sparks are Ok and fuelling goes AWOL... presume then that you now know sparks are always present

[Mr Bean]

Didn't ask the other day, but have you set/reset/checked the throttle idle cut-off setting? That's often said to be soemthing needing setting-up accurately before anything else.

You appear to working down the line of thought that sparks are Ok and fuelling goes AWOL... presume then that you now know sparks are always present

Yes sparks and injection pulses are on during fault but in the absence of a TDC sensor I couldn't be absolutely sure that they are synchronised with the mechanics. To be frank and after many years of "diagnosing" progresively more complicated kit I am rue to re-adjust anything not actually suspected to be connected to the problem on the "only change one thing at a time" basis. I have another mate who is hell bent on logging all electrical voltages and resistance values together with oscilloscope traces of spark and injection pulses for the engine running condition and seeing what if anything changes when the fault is on. This looks tedious but... Anyway I have booked another tow in later on today in case the replacement ECU doesn't do the trick.
Cheers
Ken

[HarryMann]

Well ken, then at least check that the cut-off throttle setting thingy doesn't measure up a mile out... i.e. check but don't adjust.

[Mr Bean]

Well ken, then at least check that the cut-off throttle setting thingy doesn't measure up a mile out... i.e. check but don't adjust.

Good thinking Batman! I am sure we already did that as we think we have gone throught the whole lot but another check wouldn't hurt.
Regards
ken (Boy Blunder)

[blackdog]

Gone through a similar scenario the last week or so too Ken. Fault occurred intermittently about 10 to 20 minutes into a test run, checked all the earths, ignition components etc. Luckily having two vans to change stuff between to prove serviceability, AFM, ECU, coil. dizzy, ht leads etc.
Eventually the van wouldnt start at all. Traced the fault to a bad connection on the fuel pump supply loom behind THE AFM. Terminals looked a bit green so tried to open plug/connector and one of the wires crumbled away in my hand. Obviously the connection had been going for some time and offering a high resistance so fuel pump wouldnt be getting full power.

After that van refused to run until idle stab unit was bypassed so double fault really!!?

Don't give up!
Brian

[Mr Bean]

Gone through a similar scenario the last week or so too Ken. Fault occurred intermittently about 10 to 20 minutes into a test run, checked all the earths, ignition components etc. Luckily having two vans to change stuff between to prove serviceability, AFM, ECU, coil. dizzy, ht leads etc.
Eventually the van wouldnt start at all. Traced the fault to a bad connection on the fuel pump supply loom behind THE AFM. Terminals looked a bit green so tried to open plug/connector and one of the wires crumbled away in my hand. Obviously the connection had been going for some time and offering a high resistance so fuel pump wouldnt be getting full power.

After that van refused to run until idle stab unit was bypassed so double fault really!!?
Don't give up!
Brian

Yes I had a double fault a couple of days ago when I busted a wire on the engine temp sensor while fumbling with temp sensor two plug on the stat housing and couldn't see what I had done. A valuable couple of hours testing time lost and a blow to an already deflated ego! You begin to feel that inverse Midas touch coming on. You know when everything you touch turns to poo! However this afternoon I managed to get it to die after about 30 miles of back and forth between A1(M) J's 7 & 10 and the substitute ECU did the trick while re-installing the original killed it again. This is just what I was hoping for and if it indeed is as simple as that I am well pleased. Time will tell but for the moment I will sleep easier tonight.
I have to say I am chuffed to pieces with all the advice and help I have had on this forum. I don't feel so lonely now. (Akon number playing in the background and surrounded by Weatabix type glow)
Thanks again everyone
Ken