Poor man's PI Fuel pump check?

[Agile]

Dear Forum,

 

I'm new to this forum as well as the new owner of a '74 TR6PI.

 

I'm faced with an issue quite similar to what Johnny1970 describes here http://www.tr-regist...showtopic=35414 as well as several other post in various forums. My actual question is at the end of this post, the first bit is on the issue to 'paint the scene'. so feel free to skip to the end

 

Problem

The engine starts reasonably well and if driven on the highway, runs smooth. Quite fast if needed actually. However, if I end up in traffic jam or enter a city (e.g. slow down), after a while the engine starts to perform worse and worse. As if someone pulled the choke. Eventually it stalls and it is difficult to start it again. A 10 minutes wait helps, but the same will happen again. When this is happening, the sound of the fuel pump varies (with seems to have a direct impact on the engine). It has a Bosch 0 580 254 996 fuel pump. It has a 'long' Pressure Relief Valve (PRV). The pump is mounted below the fuel tank.

 

Steps taken/checked

- choke bowden cable moves the lever on the measuring unit maximally back in 'no choke' position

- tried a new Bosch 0 580 254 984 pump, no improvement. It seemed worse almost.

- got another (can't be new...) Bosch 0 580 254 996 pump, this one is currently mounted

- new fuel filter

- return line from PRV to tank is not blocked

- body of the pump measures up to 60 degrees C when the problem occurs (IR surface thermometer)

- installed a fuel pump relay and new wiring directly from the battery

- checked that there is no huge fuel flow via the return line from the metering unit in the front

- checked with a 'cold' pump during idling as well as with just the pump running the amount of fuel flowing back from the PRV in the tank: next to nothing (I disconnected the return line from the tank to actually see any flow). When the pump is hot (and the problem occurs) and the pump starts to vary in RPM, small amounts of return-fuel can be seen flowing back at the pump RPM peaks.

 

My idea (obviously not validated!):

Initially I thought that the pump pressure was too low (suggested in many fora), but since the 984 pump and the second 996 pump did not help, I assumed the pressure is sufficient (still not 100% sure though). The poor performance at low speeds and during idling is perhaps caused by too high fuel pressure leading to the engine running way too rich. Caused (again, this is just an idea) by a non-functioning PRV leading to a too high fuel pressure and no flow of fuel at low speeds/idle via the PRV back in the tank. Which in turn leads to no cooling of the pump -> overheating -> cavitation (aka pump vapor lock - right) -> engine dies. etc.

 

Question

How much fuel should one roughly see flowing back from the PRV into the tank with just the pump running?

Is this an acceptable poor-man’s way to first order check if the pump/PRV are working in harmony?

 

And since the above is just an idea and I'm just a starter, any other suggestions?

 

I have just ordered a fuel pressure measuring device which will certainly tell me more. In short I will also be able to test a brand new PRV.

 

Thanks in advance!

[Guest ntc]

Welcome?

You should see a constant flow back to the tank engine running or not

[Agile]

Hi Neil,

 

Thanks. No flow is visible. So, as there is enough fuel in the tank, the TR6 is ok on the highway and the voltage on the pump is OK:

1. pump pressure too low
   -or-
   
2. PRV sticking (in closed position)
   

 

Could my logic hold?

 

Regards,

Wytze

[Guest ntc]

Open the fuel cap and you should hear it return, if not the prv should be the first point of call, however your meter will tell you if the pump is just doing it's job. Your logic is good

[Agile]

Hi Neil,

 

The fuel tank in my TR6 has a return pipe that runs all the way to the bottom of the tank, e.g. you cannot hear the return fuel flowing. I understood that in later TR6PI's (mine is '74) this was a change in the fuel tank together with a 'build in' swirl chamber to avoid fuel starvation while cornering. If you blow on the return line and it sounds like a straw in a glass of lemonade, you know which one you have.

 

In any case, awaiting the arrival of the fuel pressure test rig as well as the new PRV. Keeping fingers crossed.

 

While on PRV's: while ordering, I noted two PRV versions: "Lucas" and "Bosch", seem the difference is the factory set pressure. This does not make too much sense to me since the metering unit wants 106-110 PSI, imho regardless of what pump is used. Any ideas?

 

Wytze

[Peter Cobbold]

A correctly performing PRV should be able to dump the full output of the pump to the tank. At tick-over the amount of fuel taken to run the engine is a tiny proportion of this. At speed under load more fuel runs to the engine, less through the PRV. At tick-over with a poor-flowing PRV the fuel flowing abnormally slowly through the pump will get hot and boil - engine stalls. But at higher rpm under load the engine consumes fuel allowing more flow through the pump. which is enough to cool the pump and avoid this vapour locking.

A poor-flowing prv will show as high psi at the MU which falls when engine is under load. And that high psi will put more load on the pump which will get hotter, especially at tick over when the psi is highest.

The different specs for the PRV presumably relate to flow charactersistics of the two pumps, one needing to dump more flow to give the same 105psi pressure

[Agile]

Dear Peter,

 

Thanks for your detailed reply, I will focus on getting the return flow going!

 

W.

[Peter Cobbold]

Dear Peter,

 

Thanks for your detailed reply, I will focus on getting the return flow going!

 

W.

 

W,

Just to be clear, that's the return flow from the PRV not the leakage flow back to the tank from the MU !!

Peter

[Agile]

Confirmed, the return directly from the PRV in the boot.

[Agile]

I have just replaced the PRV with a new one (from Moss Europe). Now there is a constant flow from the PRV return line into the fuel tank! Unfortunately, the ordered 'universal' fuel pressure measuring kit (not Moss btw) which came with a huge collection of adapters, hoses, T-pieces, bit & pieces and whatever, except... those needed to fit to the fuel line thread on the Lucas Metering Unit . Hence I have not been able to measure the fuel pressure 'before' and 'after'. I just need to get some other plumbing someday.

 

In any case: the net effect is that the engine does not stall anymore after one or two minutes of idling, the fuel pump makes a relatively constant noise, city driving is not a challenge anymore, it does not feel like I forgot to push back the choke and the temperature of the pump goes up to some 31 degrees C (the ambient temperature was about 10 lower than when I measured the 60 degrees, therefore I should probably say 'about 40 degrees'.

 

The engine did develop last week (still with the defective PRV) a problem in that it did not always run on all 6 cylinders. Using the 'thumb / finger' method, cyl. 4 was detected as the problem as no 'heartbeat' could be felt. Swapping injectors 3 and 4 moved the problem to cylinder 3, so I concluded that the injector from 4 was not working. This could also be seen by looking at the spray cone of the injector: no spray cone, just a bit of leaking. As per the 'TR6 Brown Book' I used my air compressor to blow some air through it. This actually improved it, though to spray cone was still not as nice as #3. In any case it's running on all 6 again, but I think I'm in for one new injector.

 

In summary, yes! There is a poor man's Fuel Pump Check: there shall be a constant flow of fuel from the PRV to the tank when the pump is running.

 

Thanks for the advice!

 

Wytze

[badshead]

Wytze

 

Sounds like you're making progress! Your fuel pressure test kit sounds like a load of rubbish, if you search this forum you'll find references to making your own easily and cheaply from widely available hydraulic components.

 

Bill

[Quentin]

Definitely go for the recon injectors. Contact Neil (raven-k smith). I have suffered my whole year with a small cough when pulling away from junctions or from low rev cruise. It has driven me mad and led to reconditioned throttle bodies, new ignition leads and in the end under advice from others on the forum I put it down to running a bit lean when going from idle so I richened it up. Never really sorted it though and sometime it was worse than other times. However that advice was given in the knowledge that I always said my injectors were good. They were all new recon ones last year and should have been. However, a recon MU confused things for me. Another symptom was no.3 would often fail under hard load over 4500rpm. On careful inspection by someone more enlightened than me, however, it turned out that the "cone" on no.3 was a bit one sided and could not be encouraged to spit correctly. Furthermore every time it went over 4500rpm on a rolling road it failed (barely a dribble). So I changed the injector. OMG! I am in love with my car. What an utter transformation. So much smoother, quieter, stronger and no cough or stumble. I can barely believe it was something so bloody stupid and simple and took so long to find, or that it has taken me 2 years overall to get it right. It is an extraordinary transformation. The moral of that of course is that experts are pretty handy!! Oh and that 5.5 injectors just doesn't cut the mustard.

 

Cheers

Q

 

[badshead]

Quentin

 

You're making progress too - things are looking up! Le Mans here we come

 

Bill

[Agile]

Just an update.

Got a set of recon injectors from Neil (perfect!), installing is simple and straighttforward. This resulted in another big improvement. Idling is much better, misfires much less.

Next, I would like the engine to respond quicker to the trottle and to run smoother at very low speeds (e.g. 35 KMh while going through the neighbourhood). My initial guess is that it is running too lean at low revs. Let's dust off that CO-meter! Better yet: browse this forum!

W.

[Peter Cobbold]

"Running smoother at low revs" - check butterflies are all opening equally together. They should be just shut at tickover with rpm adjusted on the screw valve at front of manifold.

[Agile]

Check butterflies: would this be a good procedure to start with:

- slacken throttle cable

- ensure cold start fully released / not touching throttle linkage

- check all butterflies closed (feeler gauge 0.05mm does not pass)

as detailed on TR6 Brown Book, section 19.20.05

Since I do not have access to a 'synchro device', what is the next best way to check equal opening?

(feel free to suggest "visit a specialist" , the records of this PI show that "Power Props" has been involved before; I understand this is very well respected specialist in the Netherlands).

W.

[Peter Cobbold]

Most butterflies have worn a lip into the manifold so feeler gauge or cigarette paper method wont work well. Listening to the 'hiss' with a tube to the ear can work - I used that. Using an air flow meter is popular and no more expensive than paying a specialist. Dont clean the carbon deposits from the manifold around the butterflies - they help the sealing.

[Agile]

Hi Peter,

 

Thanks for the tip. I have not been able to practice the listening-to-hiss tip yet. However, I noted with an idling engine one can place the palm of your hand on the inlet with the following observations: cyl. 1,2,5 and 6: no suction noticed, so butterflies seem to close. On cyl. 3 and 4 however, one can notice suction, so the butterflies are not closing perfectly there. It is not very much, yet clearly different from the other inlets. This is btw in line with the feeler gauge check, which also suggested 3 and 4 not fully closing.

 

At this point in time, I'm reluctant to touch the adjustments screws (never messed with it), but it seems that this will need to happen to fix this.

 

W.

[john.r.davies]

The "Hiss Method" is very subjective. You have to have done it a lot for it to make sense.

 

What do others think of the Crypton Synchro Check?

Simple measuring device that uses a spring loaded vane to indicate flow on a scale.

Get the numbers the same across the block - job done!

 

There's one on eBay right now (not mine!)

http://www.ebay.co.u...=item3cc79c1090

 

John

Edited June 18, 2012 by john.r.davies

[tim_trinda]

[

What do others think of the Crypton Synchro Check?

John

 

 

Works for me ... however the Gunsons Carb Balancer - just doesn't!!

 

Tim

[Agile]

Dear Forum,

 

Just a follow up on the conclusion of the initial fuel pump / PRV issue.

 

With the new PRV and an (old) Bosch 996 pump all worked reasonably well, however at about 4000 rpm there was a notable dip in the engine torque. I asked the workshop if I could test with the (new) 984 Bosch pump and installed it. This did the trick at 4000 (and above ) RPM.

 

In summary:

• The original problem was caused by a blocked PRV: no return flow causing a multitude of issues, most notably the overheated pump and the fuel evaporating (= engine dies)
  
• With a new PRV, this was solved but there was a power dip after 4000 RPM
  
• Replacing the (obviously worn out) 996 pump with a new 984 solved this.
  

 

In between I also replaced the injectors as 2 were leaking.

 

To give others other some reference to a “poor man’s fuel pump check” (and btw fully in line with feedback in earlier replies above!), here are links to video clips showing you the actual return flow from the PRV:

1. (no) Return flow with blocked PRV and worn out 996 pump (http://s1048.photobu...gunitreturn.mp4)
    
   
2. Pump noise with blocked PRV with new 984 pump (making things practically worse…) (http://s1048.photobu...efectivePRV.mp4)
    
   
3. Return flow with a new PRV and worn out 996 pump (http://s1048.photobu...ow996newPRV.mp4)
    
   
4. Returnflow wit a new PRV and new 984 pump (http://s1048.photobu...wwithnew984.mp4) "now you are talking!".
   

 

Current situation is (4) and the engine runs fine. An additional notable refinement from fitting a 123-ignition conversion as well, but the PRV and the pump were key.

 

Are all problems solved? Of course not. It seems I'm now hitting the 'reasonating PRV noise due to perfectly working new Bosch pump'. We'll solve that one later.

 

Thanks all for your advice,

W.

Edited September 30, 2012 by Agile

[Agile]

Ordered and installed the 'longer fuel hose' betweent the pump and the PRV (part # RTR4048SS from Revington) which has reduced the noise notably.

W.