76 2Litre Type 2 - Hesitation when cruising at 55mph

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Minty
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76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Minty » Tue Jul 16, 2013 2:04 pm

Hi,

I am from London UK, and I own an Australian imported Bus which has developed a Hesitation / Miss problem when cruising around 55mph and i was hoping that you guys could help me out on what my next steps should be? This is my first post so please go easy on me! In the UK there aren't very many Fuel Injected buses so expert knowledge with Fuel Injection can be limited!

The bus starts and idles perfectly and accelerates under load with no problems.... However, when I come off the gas at around 55mph and then gently reapply the gas the bus hesitates and misses... I have owned the bus for 12 years and in that time it has run like a dream, it's only recently the problem has surfaced.

I have changed all the ignition system, Points/Plugs/Condenser/ HT leads/ Distributor Cap/Dis Arm and after a successful few test runs I thought I had fixed it, but the problem comes back intermittently?... The timing and advance is all set up pretty much spot on.

The fuel filter is 3 years old (6000miles) so I am going to change that tomorrow, but if that doesn't work I am not sure what to try next? The fuel pump I have noticed lately is noisy but I am not sure if its just cause I am more aware of the engine now it has developed this problem? Would a bad fuel pump cause such a problem?

Also whilst having a thorough check tonight of the engine bay, I noticed that the throttle valve does not have the 1mm clearance when the accelerator pedal is flat on the floor. It is hard up against the throttle body flange and the pedal action is not smooth on initial take up.... Could this be causing the problem? The accelerator cable looks like it has no further adjustment so should I get a new cable and lubricate the pedal mechanism or is it unlikely to be causing the problem?

Any help you could provide an English cousin would be greatly appreciated!!

Minty

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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Gypsie » Tue Jul 16, 2013 9:07 pm

Minty wrote:Hi,


The fuel filter is 3 years old (6000miles) so I am going to change that tomorrow, but if that doesn't work I am not sure what to try next? The fuel pump I have noticed lately is noisy but I am not sure if its just cause I am more aware of the engine now it has developed this problem? Would a bad fuel pump cause such a problem?

Also whilst having a thorough check tonight of the engine bay, I noticed that the throttle valve does not have the 1mm clearance when the accelerator pedal is flat on the floor. It is hard up against the throttle body flange and the pedal action is not smooth on initial take up.... Could this be causing the problem? The accelerator cable looks like it has no further adjustment so should I get a new cable and lubricate the pedal mechanism or is it unlikely to be causing the problem?

Any help you could provide an English cousin would be greatly appreciated!!

Minty
Welcome Minty. Won't no one here go hard on you fer sure...Might encourage you to think it through but that's what we're all gonna do anyway...

So here goes my stab at the issue...

You say the fuel pump started sounding different recently? This could be an indicator of a fuel flow issue but what is causing the pump to make the noise? (he says, thinking out loud...)

Could be a fuel restriction.. I didn't see a new fuel filter on your list? Are all the lines sitting all nice and unkinked? ...How's the fuel pressure regulator? is it adjustable? is it hooked up to the right vacuum line? (i have seen this one and the vac advance vac lines get switched around accidentally).

You could do a fuel flow test by disconnecting a line in the bay and following the bentley procedure for testing and measuring flow rate to see that gas is being delivered in enough volume to do the job. How is the condition of the tank? could you have a sea of rust floating around near the outlet line getting all clogged as fuel is drawn out of the tank?

Another possibility is some vacuum issue that is effecting performance(something like a vac leak not allowing the pressure regulator to adjust under different conditions or adjusting timing according to the demand causing fuel starvation or missing...)

(still thinking out loud...)

All else fails you could look into your mix adjustment on the AFM though I would not go there until you have eliminated a few other things first. Someone else will chime in with, likely, a more enlightening perspective...

Keep us posted on progress so we can continue honing our troubleshooting skills...

Happy travels.
So it all started when I wanted to get better gas mileage....

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Amskeptic
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Amskeptic » Tue Jul 16, 2013 9:12 pm

Minty wrote:Hi,

I am from London UK, and I own an Australian imported Bus which has developed a Hesitation / Miss problem when cruising around 55mph and i was hoping that you guys could help me out on what my next steps should be? This is my first post so please go easy on me! In the UK there aren't very many Fuel Injected buses so expert knowledge with Fuel Injection can be limited!

The bus starts and idles perfectly and accelerates under load with no problems.... However, when I come off the gas at around 55mph and then gently reapply the gas the bus hesitates and misses... I have owned the bus for 12 years and in that time it has run like a dream, it's only recently the problem has surfaced.

I have changed all the ignition system, Points/Plugs/Condenser/ HT leads/ Distributor Cap/Dis Arm and after a successful few test runs I thought I had fixed it, but the problem comes back intermittently?... The timing and advance is all set up pretty much spot on.

(HEY GYPSIE, RIGHT HERE ON THE FUEL FILTER)
The fuel filter is 3 years old (6000miles) so I am going to change that tomorrow, but if that doesn't work I am not sure what to try next? The fuel pump I have noticed lately is noisy but I am not sure if its just cause I am more aware of the engine now it has developed this problem? Would a bad fuel pump cause such a problem?

Also whilst having a thorough check tonight of the engine bay, I noticed that the throttle valve does not have the 1mm clearance when the accelerator pedal is flat on the floor. It is hard up against the throttle body flange and the pedal action is not smooth on initial take up.... Could this be causing the problem? The accelerator cable looks like it has no further adjustment so should I get a new cable and lubricate the pedal mechanism or is it unlikely to be causing the problem?

Any help you could provide an English cousin would be greatly appreciated!!

Minty
Right cheers,
Yes, please do address the niggling concerns spelled out above. Lubricate everything that appears to need it. However, distinguish between the symptoms of your request for more power and the engine's actual providing of your request.
a) a sticky misbehaving accelerator pedal cable etc makes your request seem spastic, but if you *do not move the accelerator during acceleration*, any hesitation is coming from the engine's attempt to provide power.
b) you have full ability and control over all operating mechanisms to make them smooth and properly adjusted, so of course deal with them now. We need to edit out any stupid variables now.
c) noisy fuel pump and dirty fuel filters go together like Lucas and MG on the side of the road.

Keep us apprised as you delete variables!
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Bleyseng
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Bleyseng » Tue Jul 16, 2013 10:10 pm

Is the vacuum advance working properly? Does the vac can hold a vacuum and if a vac pump is used and pulled a 15hg vacuum does the plate move smoothly? Check the vacuum hose layout per Ratwell.com pictures.

Oh yeah, welcome!!!!!
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

Minty
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Minty » Wed Jul 17, 2013 11:37 am

Hi... thank you all for your advice and for going easy on me! I have ordered a new fuel filter and accelerator cable to eliminate any sillys...

But also

I have checked the vacuum lines as per Ratwell's brilliant diagrams and I have notice a difference on my set up! My Distributor Can is connected to the throttle body only, it does not have a T piece in it and does not have a connection to the Air Cleaner also?

Could this be causing / contributing to the problem? I take it the a hose is supposed to connect to the small spigot which I have photographed? The big spigot is blanked off above it, I am not sure what this connection is for?
image.jpg
Air Cleaner Connections

I also noticed that the hose used to connect the Air Plenum to Fuel Pressure Regulator is less than 5mm hose in the centre section but uses 5mm at either end? Could this be limiting pressure to the Fuel Pressure Regulator and also contributing to the problem? I had the engine overhauled 3 years ago where I believe these irregularities with the vacuum hoses have occurred..

Thanks again for your help, I will keep you posted with my developments... I felt pretty alone when I first started trying to diagnose this problem but now feel that I have Team America trying to help me!

Minty

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Amskeptic
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Amskeptic » Wed Jul 17, 2013 12:42 pm

Minty wrote:Distributor Can is connected to the throttle body only,
Could this be causing / contributing to the problem?

hose used to connect the Pressure Regulator is less than 5mm hose in the centre section but uses 5mm at either end? Could this be limiting pressure to the Fuel Pressure Regulator and also contributing to the problem?
Perfectly expected and normal to have the EEC valve out of the advance loop.

Any limit in vacuum supply would only increase fuel pressure, as it is the intake plenum vacuum that allows fuel to course through the return line at specified pressure. Remember that vacuum is static, there is no airflow. A small hose only slows response time. Once any vacuum-actuated diaphragm is pulled, you can maintain vacuum through a 1/2mm hose (but don't do that).

You can do an experiment if you like:
Disconnect the vacuum hose from the fuel pressure regulator and plug off the now dangling vacuum line.
Drive the car.
Report behavior, i.e. better/same/worse.
It is the quick and easy fuel mixture boost that will tell us if your engine is feeling:
a) too lean currently - will run better with FPR disconnected
b) just right - will run slightly better at speed but minor difference at idle
c) too rich - will run worse with FPR hose off, and may exacerbate bucking/hesitation

Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Minty
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Minty » Wed Jul 17, 2013 1:01 pm

Colin,

Thanks for this... So just to confirm when I do this experiment disconnecting the vacuum hose from the Fuel Pressure Regulator, should I also not connect the Distributor Can to the Air Cleaner?

Thanks

Minty

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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Amskeptic » Thu Jul 18, 2013 6:13 pm

Minty wrote:Colin,

Thanks for this... So just to confirm when I do this experiment disconnecting the vacuum hose from the Fuel Pressure Regulator, should I also not connect the Distributor Can to the Air Cleaner?

Thanks

Minty
Vacuum advance should be plumbed directly the throttle body. The air filter EEC valve is not necessary to this diagnosis, nor should it be hooked up unless you confirm that it is not leaking at the vacuum connection.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Minty
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Minty » Fri Jul 19, 2013 12:34 am

Thanks Colin for the confirmation... I am working on the bus tomorrow and will give an update on I figure out...

Minty
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Re: 76 2Litre Type 2 - Hesitation when cruising at 55mph

Post by Minty » Sat Aug 03, 2013 1:32 pm

Hi, I have finally fixed my bus! I replaced the accelerator cable and the fuel filter and the hesitation was still happening, so I turned my attention to the LV wiring and disconnected the white wire from the Coil to the CPU and pulled the wire out completely, thats when I noticed that a small section had been chaffing on the engine case and had worn the insulation down to the wire!

I taped it up with Electrical tape (temporary repair) and she hasn't missed a beat since!

Thanks for all your help and advice, this forum is excellent and I have learnt so much from the other posts that I am no longer scared of my Fuel Injected system...

Thanks again

Minty

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