TR5 Injection issues intermittent

[zzzzdave]

Currently trying to solve an intermittent fuel injection issue, have read many old posts on the subject but this where im currently at 

Metering unit refurbished  , injectors refurbished , new injector hoses ,  modern PRV , new fuel lines , clean tank .

symptoms , losing fueling on an injector after 30 mins run , car stands for 15 to 30 mins , restart and runs on 5 cylinders , done it twice in the last week, and many times last year.

Managed to fault car whilst fault was still present , and no 3 injector no fuel , others weak pulse, pulled number 3 injector and pulled end of injector fuel came out , let go of end fuel stopped, left it for 15 mins to have a think went back to it , pulled injector again started injecting again fault cleared . Last  year same happened , but other injector numbers , hence why i got metering unit refurbished.

Now put a fuel pressure gauge on MU, and good solid 102PSI, tried to replicate fault, another run out , stand car , restart all good, so plan is to run local runs , see if i can get it to fail and check fuel pressure gauge if fault appears.

For a PI car its starts brilliantly hot or cold on all cylinders, alot better than the TR6 i had previously.

So symptoms suggesting to me fuel pressure intermittently dropping , but cannot prove it yet,, im checking fuel tank vent this morning and look inside tank for any plastic debris etc intermittently blocking tank outlet. 

so my focus at moment is fuel pump set up ( came with car unknown to me ) , looks a Bosch pump setup, seems when i research types of pumps Rimmers/Moss sell Bosch type pump setup with Bosch Filter Pre pump, but the likes of TR Trader/Prestige there pump has a sytec bullet pre filter , Bosch type pump, then Bosch high pressure filter .  I also read an old post from Stuart that Bosch pumps dont like pre filter restrictions .

So my pump setup is as picture , So from tank I have Bosch filter 0450905005 F5005  ( fitted correct direction)  this then feeds into the Bosch type pump and its high pressure output goes to modern new PRV etc . So when i look on MOSS site Bosch filter replacement is 0450905005, when i look on Rimmers site Bosch filter replacement is 0450905021 F5021, I cannot find anywhere on Google what the difference is between the filters , im thinking do i have the wrong filter in pre pump thats unsettling the pump sometimes , filter was new last year , changed like for like  so not blocked , 

Anybody got any theories i can follow , do pumps drop pressure intermittently ? which im still trying to prove with pressure gauge 

Dave

[zzzzdave]

Just to add a bit more , fuel pump has proper earth  bonding point, fed by relay , and extra heavey duty feed via its own fuse box , via blade fuse from direct battery feed, but i will measure volts to check no losses anywhere, the pump is quiet , and does not change its note when fault is on, when fault is Not present car runs great , and high revs and spirited driving it goes great which suggests its not a flow issue 

thanks Dave 

[trchris]

Hi Dave could you run with the pressure gauge in situ? I would suspect pump if pulses are weak after having metering unit overhauled 

Chris

[zzzzdave]

Plan is to run car with pressure gauge in place and see if I can get fault to come on 

[Waldi]

Hi Dave,
a possibility is that you draw air into the system (pump), either via a leak between tand and pump-inlet or via the tank (is the tank baffled, or is there a relation with tank fuel level?

Another possibility is insufficient flow. You can measure the flow rate if you disconnect the prv-return rubber hose, use a suitable 5 or 10 l container and measure the time to fill the container. Minimum req. flow per the original specifications is around 90 liter/hr, so 1.5 liter/min. Do this test with a helper (safety).

BTW:
The system does not hold pressure once switched off with an original prv, not sure how the modern prv that you have behaves.

Waldi

[PodOne]

1 hour ago, Waldi said:

The system does not hold pressure once switched off with an original prv, not sure how the modern prv that you have behaves.

Waldi

Hi Waldi

The modern PRV doesn't hold the pressure either. I wonder if the modern PRVs get sticky like the old ones which would possible cause the problems described. Having the pressure gauge in the cockpit would help seeing what's going on.

Andy

 

[zzzzdave]

The tank is a revington extra capacity alloy tank with baffles etc , tanks is 3/4 full so no shortage of head of fuel. 

Ill have a look at checking the flow as you suggest and see what that tells me , Thanks for the further Ideas 

 

Dave 

[michaeldavis39]

Most Bosch petrol fuel filters are 8-10 microns. Last year I was having similar problems to this gentleman until I replaced the Bosch filter for a Sytec bullet filter with a metal 100 micron fuel filter- was always number 3 injector too!. Anyway my injectors behaved after this change so I highly recommend doing this.

[zzzzdave]

Looked in tank, its spotless , air vent good and so is 12v feed to pump, need to check flow rate tomorrow. Just been out for 45 mins drive, stood in many traffic queues getting warm never flackered . 

just found this on google search 

"Placement: Fine filters (like 10-micron units) are almost always placed after the fuel pump because they require pressure to push fuel through the dense media. Coarser filters (e.g., 100-micron) are used before the pump as "pre-filters" to protect the pump itself without restricting gravity-fed flow. "

Michaeldavis39 this stacks up with what your saying , 

ill keep at it over the weekend, then i think ill change filter arrangement , with sytec bullet pre pump, and high pressure bosch filter after pump and see if that gives me consistency 

 

[Waldi]

Dave,
Opinions about the best filter set-up differ. I use a large Sytec suction filter with fine paper element inside. No discharge filter. Note the original PRV and the MU both have a coarse inlet strainer.

I preventively replaced the filter after approx. 5 years in operation, not because I had issues. The number is Sytec SSF2012. I prefer to protect my pump, a course filter will give less protection. 

Others use a discharge filter or a combination of both and happy with that.

Succes,
Waldi

 

Edited April 24 by Waldi

[michaeldavis39]

I forgot to mention- Bosch pump will usually have its own built in filter which many dont realise.

[stuart]

I always fit the really big Sytec filter pre pump and that’s it 

Stuart 

[Chris Hale]

9 hours ago, stuart said:

 

I always fit the really big Sytec filter pre pump and that’s it 

 

 

My set up has been like that for over thirty years with no issues

[Paul Hig]

Not an expert, but you say pressure at 102 psi, which would appear low, shouldn't it be between 106 and 110 psi?

 

[stuart]

3 hours ago, Paul Hig said:

Not an expert, but you say pressure at 102 psi, which would appear low, shouldn't it be between 106 and 110 psi?

 

Depends on the pump, some of the Bosch ones will shift a lot of fuel so need a lower setting .

Stuart.

[Paul Hig]

1 hour ago, stuart said:

Depends on the pump, some of the Bosch ones will shift a lot of fuel so need a lower setting .

Stuart.

Thanks Stuart

Never ending learning curve 😎

[zzzzdave]

 

So just been out for a run, not lost any cylinders , but the fuel pressure is not rock steady as it should be 

Hopefully these links work, the top one is TRTrader reel showing rock steady fuel pressure, the bottom link is video of my fuel pressure after a run, wavering pressure 

https://www.facebook.com/reel/1116593658443881

https://photos.app.goo.gl/3pMXtV4LWWjGbBKe7

Its either pump or PRV , My thinking is the pump is on its way out , PRV is 18 months old so assumption is it should be ok 

 

Thoughts 

[Waldi]

Looking at the 2nd video I think this is related to not optimal electrical supply to the pump.

With idle rpm there is almost no fuel consumption, but the pump will react immediately on a lower voltage. This can cause the variations in pressure.

I suggest measuring the voltage over the pump connections, and compare with battery voltage.

Are you still on the (low rated) original Lucas alternator?

Also, poor contacts (spades or nuts not firm, corrosion) can cause a voltage drop.

The electrical current to the Bosch pump is high (approx. 9-12 A depensing on pump type) so any poor connection should be avoided.

Waldi

[John McCormack]

On 4/25/2026 at 2:42 AM, zzzzdave said:

Looked in tank, its spotless , air vent good and so is 12v feed to pump, need to check flow rate tomorrow. Just been out for 45 mins drive, stood in many traffic queues getting warm never flackered . 

just found this on google search 

"Placement: Fine filters (like 10-micron units) are almost always placed after the fuel pump because they require pressure to push fuel through the dense media. Coarser filters (e.g., 100-micron) are used before the pump as "pre-filters" to protect the pump itself without restricting gravity-fed flow. "

Michaeldavis39 this stacks up with what your saying , 

ill keep at it over the weekend, then i think ill change filter arrangement , with sytec bullet pre pump, and high pressure bosch filter after pump and see if that gives me consistency 

 

My TR6 with a Bosch pump has the filter after the pump. I have small general purpose filters before the pump but the main filter after.

It was like this when I got the car 10 years ago and I have been told by real experts the filter must be after the pump. Obviously others have different approaches.

Edited April 26 by John McCormack

[zzzzdave]

volts is good to the pump, no issue with relay , earths are good,  have ordered a  new Sytec pump see if that resolves it,

 

Dave 

[PodOne]

4 hours ago, zzzzdave said:

volts is good to the pump, no issue with relay , earths are good,  have ordered a  new Sytec pump see if that resolves it,

 

Dave 

Agree with Waldi I would run a 12v supply and earth direct to the pump to rule the wiring out and go from there. PRV although newish may still be sticky or as you say the pump may be on the way out.

[Dave I O W]

On 4/23/2026 at 10:44 AM, zzzzdave said:

Currently trying to solve an intermittent fuel injection issue, have read many old posts on the subject but this where im currently at 

Metering unit refurbished  , injectors refurbished , new injector hoses ,  modern PRV , new fuel lines , clean tank .

symptoms , losing fueling on an injector after 30 mins run , car stands for 15 to 30 mins , restart and runs on 5 cylinders , done it twice in the last week, and many times last year.

Managed to fault car whilst fault was still present , and no 3 injector no fuel , others weak pulse, pulled number 3 injector and pulled end of injector fuel came out , let go of end fuel stopped, left it for 15 mins to have a think went back to it , pulled injector again started injecting again fault cleared . Last  year same happened , but other injector numbers , hence why i got metering unit refurbished.

Now put a fuel pressure gauge on MU, and good solid 102PSI, tried to replicate fault, another run out , stand car , restart all good, so plan is to run local runs , see if i can get it to fail and check fuel pressure gauge if fault appears.

For a PI car its starts brilliantly hot or cold on all cylinders, alot better than the TR6 i had previously.

So symptoms suggesting to me fuel pressure intermittently dropping , but cannot prove it yet,, im checking fuel tank vent this morning and look inside tank for any plastic debris etc intermittently blocking tank outlet. 

so my focus at moment is fuel pump set up ( came with car unknown to me ) , looks a Bosch pump setup, seems when i research types of pumps Rimmers/Moss sell Bosch type pump setup with Bosch Filter Pre pump, but the likes of TR Trader/Prestige there pump has a sytec bullet pre filter , Bosch type pump, then Bosch high pressure filter .  I also read an old post from Stuart that Bosch pumps dont like pre filter restrictions .

So my pump setup is as picture , So from tank I have Bosch filter 0450905005 F5005  ( fitted correct direction)  this then feeds into the Bosch type pump and its high pressure output goes to modern new PRV etc . So when i look on MOSS site Bosch filter replacement is 0450905005, when i look on Rimmers site Bosch filter replacement is 0450905021 F5021, I cannot find anywhere on Google what the difference is between the filters , im thinking do i have the wrong filter in pre pump thats unsettling the pump sometimes , filter was new last year , changed like for like  so not blocked , 

Anybody got any theories i can follow , do pumps drop pressure intermittently ? which im still trying to prove with pressure gauge 

Dave

Hi you could try changing the bango fitting on the entry to the pre filter and put a straight through fitting for perhaps a better flow of fuel, And it looks to me that the rubber pipe

 

from the tank to the filter is a little bit squashed,

Hope this helps

Dave.

[Richardtr3a]

How is the car running now some weeks later ?

My TR3A had similar problems and the answer after many years was an expensive solid state RB106. I had better starting and it  ran really well. I had spent a  lot of time and money on the carburettors and in the end it was the IGNITION.

This may apply to your TR5 and I would be interested in an update.

good luck 

Richard

[Paul Hig]

Had starting problems with my TR6 (CP enfgine) and started on less than 6 cylinders quite often, even after engine rebuild. Turned out the seals in the metering unit were failing. Refurb metering unit and now all good, so might be worth a check

[zzzzdave]

hi , metering unit is refurbished ,I have just received a new sytec pump setup, busy installing it, let you know if this solves the issue

thanks Dave