Help with misfire fault please

[yknot]

I 'cleaned' mine with a squirt of electrical contact cleaner but, to be honest, it didn't look contaminated at all!

With the high voltage you're getting from testing the MAF sensor it looks goosed plus you now have a fault code logged. Is there anyone close to your area who would let you swap theirs to test??

[blitzracing]

It wont be dirt- it will be a failing semiconductor on the circuit board inside, having been cooked by the TVR exhaust manifold- Im surprised they last as long as they do without a heat shield.

[taylormj4]

blitzracing said:

It wont be dirt- it will be a failing semiconductor on the circuit board inside, having been cooked by the TVR exhaust manifold- Im surprised they last as long as they do without a heat shield.

Thanks Mark,
I'm reasonably handy with a soldering iron. Is it something that is repairable / common component that goes ?

I ran Rovergauge again tonight with the MAF reading on "direct" and was getting oscillations from around 29 up to in the 50s. Caused a stall at one point from idle.
I have videoed the Rovergauge screen to show everyone what I am seeing and will try to get a link to it sorted soon.

[blitzracing]

You have to dig your way in through the cover with a sharp knife- its well glued in with silicon. There is an Op-amp in there you could try swapping if you can get a 20 year old component- but Ive never managed to get a circuit diagram- also the hot wire sensor has steel connections that dont resolder well- and you have to clip the connections to remove the circuit board anyway.

[taylormj4]

blitzracing said:

You have to dig your way in through the cover with a sharp knife- its well glued in with silicon. There is an Op-amp in there you could try swapping if you can get a 20 year old component- but Ive never managed to get a circuit diagram- also the hot wire sensor has steel connections that dont resolder well- and you have to clip the connections to remove the circuit board anyway.

Thanks Mark.
What I am still a bit confused over is how fiddling with the connector wires could have made the system suddenly work again and then a short period of high revs made the problems restart. Wouldn't you expect a MAF circuity failure to remain once it had started ?
Very odd.

If the MAF is shot. Is it worth considering alternatives to the 5AM ?

Edited by taylormj4 on Wednesday 11th June 12:53

[blitzracing]

I cant say why the fauly is intermittent , but you could replace it with a Bosch unit, like the kit ACT sell- but I think there is a market here for someone like Joolz of kits and classics- he has access a rolling road, and the facility to remap the 14CUX for the Bosch AFM- so he can do a map / chip with the AFM, but he might be treading on the more established tuners toes if he does. Id also quite like to test one of the cheap pattern 5AM at some point to see how good / bad they are.

[taylormj4]

Hi Blitz,
I'll take a look at that kit - think I found it a day or two ago actually.
However, I'd thought I'd read that the AFM isn't the place to start with increasing a standard engine's ability to breathe. So thought I'd be better off sticking standard and looking at the inlet manifold / trumpets if I wanted to go down that route. I've already fitted the smooth bore pipes.
I don't want to go too crazy as it's a daily driver and I'm quite keen on originality but I would love to solve the low throttle opening shunting behaviour so this may be an opportunity to do that.

In the meantime, I understand that I can run the engine (maybe) with the AFM disconnected with fueling done of the TPS. Presumably fueling will be a bit approximate like this. Do you think there is a possibility of wrecking the CATs if I drive it like that ?

Edited by taylormj4 on Wednesday 11th June 17:33

[blitzracing]

The bosch AFMs are no more to buy than the Lucas so if you are buying a new AFM it would make sense to go to Bosch, but the chipping is the issue. If you could get a chip for £50 it would be a very viable swap out for the 5AM with a bit of wiring, but until someone comes up with an alternative option to the MA chip its too expensive just to replace the 5AM. And no dont run without the AFM-its get you home, not drive it around mode!

Edited by blitzracing on Thursday 12th June 12:35

[taylormj4]

blitzracing said:

The bosch AFMs are no more to buy than the Lucas so if you are buying a new AFM it would make sense to go to Bosch, but the chipping is the issue. If you could get a chip for £50 it would be a very viable swap out for the 5AM with a bit of wiring, but until someone comes up with an alternative option to the MA chip its too expensive just to replace the 5AM. And no dont run without the AFM-its get you home, not drive it around mode!

Edited by blitzracing on Thursday 12th June 12:35

Thanks. So what benefits would I likely see with a Bosch AFM on a stock engine? Also, I thought that others were now offering alternative chips to MA. Is that not the case ?

[QBee]

taylormj4 said:

Thanks. So what benefits would I likely see with a Bosch AFM on a stock engine? Also, I thought that others were now offering alternative chips to MA. Is that not the case ?

Beware - if you even could get a pre-programmed chip cheaply, there's a fair chance it won't be correct for your car. I had my engine changed, with lots of induction mods, and was sold a best guess chip for £250. I thought that was the end of it.......but I then had to spend the change from £1000 getting the thing mapped so that it ran without going horribly lean, and at the end of the mapping didn't even have the same chip that i started with.

[blitzracing]

Its a crazy world- its no more difficult to reprogram a TVR fuel map, or a best guess map- the process is the same. The difference is you have the TVR chip already, so you should you have to folk out £250 for a chip thats not much use apart from getting you to the rolling road? Apart from the established tuners, Joolz or kits and classics has successfully mapped a different AFM onto a TVR now, as he has a rolling road so best to to ask him if he wants to do a map- once he has an example he could duplicate it. The likes of me and Steve sprint have the software and hardware needed, but no rolling road or desire to practice such things on other peoples cars in case we break them!

[QBee]

Well.......it just so happens I will be popping over to Chesterfield next Wednesday to watch Jools at work on a friend's Megasquirted car, and it would be rude not to take my 14CUX clad car......just in case he has a spare five minutes.

[ButtonIt]

Now mine has started this again... A new rotor arm has fixed the starting issues, and everything seemed really good. But on Saturday I set out and had the whole drop in power issue again. Drive for a while then all of a sudden a couple of seconds of dropped power and then it kicked in again.

[taylormj4]

Bit of an update:
I have cut off and replaced the AFM connector completely. Reconnected and teh problem seemed to have been sorted. Took it for a drive, let it warm right up, gave it some revs and still fine.

Then I gave it a real boot up a hill (nearly full throttle and up to around 4500rpm) and as I lifted off the throttle, the problem started again.

RG was linked up and found fault codes of:
AFM fault
Throttle pot low/MAF hi

Is it possible for an AFM to fail under high throughput of air or when it gets hot but then work normally again when it cools and at low revs ?

The connector repair certainly seems to have helped but not remedied it completely, which is very odd.

What does the ECU have to see to register and AFM fault ?

Edited by taylormj4 on Wednesday 18th June 15:23

[blitzracing]

The ECU software is smart enough to know you cant have high airflow with the throttle shut, hence the error code with both devices listed. You could have a normal AFM output, and a break in the throttle pot track, so it gives a low voltage reading with a high AFM reading- so it might not be an AFM going high, but an intermittent throttle pot. And yes electronics can fail when hot and recover when it cools. You could try heating the throttle pot a bit with a hot air gun, and check you dont get drop outs with the RoverGauge check when you move the throttle.

Edited by blitzracing on Wednesday 18th June 21:43

[ButtonIt]

OK, try number three hundred and ten, and this seems much more like it!!

New distributor cap, rotor arm and leads from this guy

https://www.simonbbc.com/

Everything fits SO MUCH MORE snug than ever before, no play in dizzy cap, leads have a discernible "click" into place, both plug and dizzy end. Rotor arm has a much more stable feel to it...

More to the point, I found my number 8 lead had been worn through by the alternator belt!!! God knows how, or when, or why!! I feel a bit daft for not checking the whole length of the lead, but I'm pretty sure this may have been something to do with my ongoing problems.

Off to Portsmouth at 5:30am so I guess I'll find out soon enough

[taylormj4]

blitzracing said:

The ECU software is smart enough to know you cant have high airflow with the throttle shut, hence the error code with both devices listed. You could have a normal AFM output, and a break in the throttle pot track, so it gives a low voltage reading with a high AFM reading- so it might not be an AFM going high, but an intermittent throttle pot. And yes electronics can fail when hot and recover when it cools. You could try heating the throttle pot a bit with a hot air gun, and check you dont get drop outs with the RoverGauge check when you move the throttle.

Edited by blitzracing on Wednesday 18th June 21:43

Hi Mark,
I should have added that on return from the road test where the high revs caused teh spluttering to reappear, I tested the throttle pot with IGN off as follows:

Watching the RG display, I gradually opened the throttle in 1% steps from 0 to max (97%) and then back again, making sure that every 1% step was displayed. The test was successful. So it appears that the TPS is healthy (although engine bay would have cooled a bit).

I have a new AFM on the way. Went standard 5AM. Would like to have looked at a Bosch unit but I've looked at going through the MA process in the past and the guy is too busy to return calls, so it would be months probably before the car got back on the road.

[taylormj4]

New 5AM AFM finally arrived and fitted. It's actually date stamped 1997 so exactly the same age as the car funnily enough.
Car now working well again throughout all the rev range and loads.

Very thankful to Rovergauge/Blitz's lead for helping me diagnose the fault and saving me from the dreaded gradual replacement of parts until resolved technique !

I notice that the long-term lambdas are still showing -99% and -94%, caused by running with the fault. The short terms are compensating in the +ve range so car runs OK.

I presume the ECU will return the long-term lambdas back to their usual values or I could reset the ECU. Is that correct or should I be adjusting the pot on the AFM ?

Now I need to make a heat shield for the new AFM. Using some tin foil at the moment but doesn't look great.

Edited by taylormj4 on Tuesday 1st July 13:54

[QBee]

taylormj4 said:

Now I need to make a heat shield for the new AFM. Using some tin foil at the moment but doesn't look great.

Edited by taylormj4 on Tuesday 1st July 13:54

£19 would get you this off Classifieds:

http://www.pistonheads.com/classifieds/parts-and-p...

[taylormj4]

QBee said:

£19 would get you this off Classifieds:

http://www.pistonheads.com/classifieds/parts-and-p...

Ha ha thanks QBee, that looks like Brian off Confused.com !