Electrical: '98 V70R Down on power until disconnect & reconnect battery?

[acme15]

After a few minutes/miles of driving, my 98 V70R is severely down on power, I can feel it holding back severely, sometimes stutters but usually smooth just hugely slower.

If I disconnect and re-connect the battery, it is fine again for a good few minutes/miles, very smooth and goes like a scolded cat.

Car has fresh leads, plugs, coil, rotor arm, dizzy cap, and a stage 1 ECU. Other than that it has a 3" angled turbo housing, 3" turbo back exhaust, and a pipercross panel filter.

I'm starting to lose my rag lol... It has been suggested that it could be an air/vac leak causing it to adjust fuel trims as I drive and disconnecting the battery could be resetting the ECU, but it was also said that it could take a good 15 minutes for the ECU to be reset, whereas I only need to disconnect it momentarily. A few seconds is all it takes.

It is an auto to manual converted car and used to have a Rica tuned automatic ECU meaning it would violently hold back over 50% throttle, I replaced that with a manual ECU tuned by Shemtek. Improved, but it was still running badly so I replaced the ignition system, which had got me to where I am now where it runs fine for a bit, and then I need to disconnect and re-connect the battery because it goes down on power...

Any help welcome!!

[DaveNP]

I'd say it sounds like it's going into 'limp home' mode, disconnecting the battery clears whatever fault has occurred and off you go again. So we're back to the old story, read the codes, when it's in limp mode, and it may well tell you what's wrong rather than guessing at a string of replacement bits

[PNuT]

4.4 or ME7?

[acshortt5]

Originally Posted by PNuT

4.4 or ME7?

OP says it's got rotor arm/dizzy cap so it will be 4.4

[PNuT]

Originally Posted by acshortt5

OP says it's got rotor arm/dizzy cap so it will be 4.4

Good point!

Codes would be a good start, fuel trim data would be handy....

Boost pre & post would also be handy to know.

[acme15]

Hi guys, yeah 4.4 as it isnt CoP, I will see if I can pull the codes. How can I gather the fuel trim data? I have the correct type of OBD cable and a laptop, just need software?

I am part way through fitting a boost gauge so I will see if I can get that done and then report back on boost levels. I am fairly sure it isn't boost related though as I can feel it holding back as though it is fuel or ignition related.

I don't think it is ignition for two reasons, the first being that I've already replaced everything (aside from the distributor, but done plugs, cap, arm, leads, coil) - So I think it is fuel related, possibly because of a vacuum issue or a sensor issue.

Anyone have any tips on which sensors to test, where they are, and how I should test them?

Many thanks

[sdg1970]

It'll either be Lamda sensors, split vac hoses, MAF and coolant temp sensor. I replaced ALL the above on mine to get it running right over a period of 18 months.

[Mkengineering]

Money it's the temp sensor.

Or a vac leak somewhere

[PNuT]

VOL-FCR may give you live data and fuel trim info although I would not be certain on a modified ecu! live data doesn't work on my ecu.....

I would suspect MAF, when I have had faulty O2 it ran rich as F*** but went quite well under WOT conditions!

A vacuum leak would be a vacuum leak regardless of the battery disconnect?

[acme15]

I think the logic is that whatever issue there is, whether it is a vac leak, sensor issue, etc, is causing the fuel trims to adjust gradually, and it is reset after disconnecting and reconnecting the battery. But that may be wrong.

I took a datalog on tunerpro:

https://drive.google.com/file/d/1A1I...w?usp=drivesdk

If anyone is able to extract any meaningful info from it I'd be forever in your debt, because I can't... The values all seem messed up.