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Tii hesitation and popping under load question


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Hi all, I'm finally finishing a long restoration on a '73 Euro Tii.  I've gone through all the items concerning setting and troubleshooting but still have a hesitation and popping occurring under load.  The engines runs well not under load although there is a slight miss.  

My question is:  I have an elevated fuel pressure in the pump of 32lbs,  not sure if that would cause the injectors to fire off time?  From what I understand and seen of the pump head is that it is a fuel rail with intake and pressure valves.  The pressure valve will compress the fuel based on the pump being synchronized with the crank via the belt.  The high-pressure fuel will then cause the injector to open on that line.  The fuel return valve just opens up based on spring tension and a simple value to let excess fuel out to the tank.   So...a higher pressure in the "fuel rail" will cause fuel to remain there longer but should not cause the pressure valve on that line to open up quicker will it..seems like that valve would open when fuel is compressed in that valve to that pressure.   That's my take but please edjumacate me!  I'm losing my mind on this...it's a final step to getting this thing on the road finally.   

Some history:   Car sat for about 8 years but was in good shape.  Engine was totally rebuilt by a very experienced BMW mechanic.  When the engine went in, TDC was synced at cam, pump drive.  OG distro, new head on pump as the old one had bad valves, new one looked great and valves looked clean.  Have not had the injectors checked but they looked good and I soaked them in Seafoam.  Warm up circuit is working fine(10mm rise after warm-up).  Has a new Pertronix in it although the magnetic trigger sits about half-way down the sensor but that's the only way the rotor will fit correctly.   Pertronix says that is fine.  Distro cap was new but showing build-up on the inside(the annodes that go to the plugs), this seems odd given it was a new distro and I've not driven the car much.  It does have a pertronix flamethrower coil on it.   I've driven it and played with the distro position, driven again and aga but cannot get the surging/popping/lack of power to stop.  Plugs are black and a little wet looking, cleaned them and driven again and same issue. Any ideas, especially the question on the higher pressure in the fuel rail?  Tailpipe look does lean out after it warms up(which takes forever in the garage) so the warm up system is working and I can see 10mm showing when warm.    I have not touched the "verboten" screw yet...   All FI linkages are new and set to specs(length).  I've set all settings based on manuals.   I'M GOING INSANE WITH THIS...  P.S.  If anybody in the PNW area know these things really well I would love some help.  I live just North of Seattle(Bothell area), thinking another set of eyes may help.   Help me Obe Wans...:)

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Some follow-up questions/ideas: 

-Should I play with the verboten screw since the KF pump head is not original to the pump?  My thought is that the pump/head were bench-tested and set as a unit so a new head may have thrown it off so needs a new adjustment?

- Do these cars run rich till warm and maybe it's running lean when warmed up so adjusting the warm up "hat" to richen it up may help?  

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Thanks AVG!  I've ordered a new rotor/distro cap and plugs and will set timing again after they are in just to rule out those issues.  I had iridium plugs in there so not sure they were best so went with the NGK BP5ES based on the forums.  I'll get back to this thread after those are in and timing set again and road tested.

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Hi

You didn't mention if the distributor advance curve is correct.

 

You can check this with an advance timing light at say, 500 rpm increments.

 

My personal feeling is to throw the pertronics in your neighbors pool. Points are ~$3.15 a pop.

 

I'm not sure what a flamethrower's specs are, but there may be something there too.

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Thanks all.  Plug wires are new, pretty much everything is(nut and bolt resto).  But....I have not had my distro tested so good idea and I do need to buy a decent timing light.   I do have points and condenser ordered as well just to eliminate some variables as it does seem like an electrical/timing issue.  It's good to know my thoughts on the higher pressure are on point which makes sense.   Any other thoughts on the idea of the head/body of the KF pump are not OG and that the verboten adjustment may have to be made if all else fails?  My plan is to first put new plugs/distro cap/roter/points in and time and drive.  If that doesn't work, I'll do slight adjustments first to the warm up "hat" drive adjust repeat,  then if needed, play with the verboten screw in small increments, mark OG first then mark and log all small adjustments and drive/test.  Man...if this thing was a Ti I'd be done a long time ago...but...this car is a great example of a Euro Tii with dogleg, etc. so I want to keep it as was designed with some minor personalization.   These cars are an Icon of design and engineering for sure.   Think about the complete crap that came out of Detroit in the early to mid 70's compared to these beauties.   I'm going German recently as I just did a resto on a Vanagon as well.   

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8 minutes ago, 73InkaTiiEuro said:

Yup, realize I need to invest in getting a bung installed on the downtube and an AFR gauge.  I tried to find a reasonable AFR meter that I could put a sensor in the exhaust pipe but no luck.  Any input on where on the downtube to have the bung installed on the Tiis?

I installed the bung aft of the downpipe. Do a search here for AFR gauge suggestions.

 

Cheers,

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Already some good advice here.  Don’t make multiple changes at the same time.

1) Examine your distributor housing noting the Bosch numbers and letters. IIRC, the Euro tii uses a different distributor than the USA models.

 

2) A worn out distributor will cause lots of running issues. I highly recommend sending it to Advanced Distributors for a rebuild and customized advance curve.

 

3) Some new spark plug wires are junk.  Make sure the ends are properly attached to the wire leads and use a digital VOM to check their resistance.

 

4) Install a wideband 02 sensor for tuning the car. You are just guessing without one.

 

5) Remember the factory settings for a tii are just that. Don’t assume the car will run properly using the factory published settings - some tweaking using the WB 02 sensor may be required.

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Thanks Jim, those are great ideas and I think you're right on #5.  The engine builder did shave the head a little and having a new KF pump head on the OE KF pump body would add some variables to the equation and needing to tweak a bit.  I'll be creating a little chart to keep track of any changes I make to the settings and mark them so I can methodically work through them.   And yeah, I think the 02 sensor is a must, not a luxury on these cars.  I am going to keep posting my approach, changes and results so I can add back a little to the forums.  

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7 hours ago, 73InkaTiiEuro said:

Thanks Jim, those are great ideas and I think you're right on #5.  The engine builder did shave the head a little and having a new KF pump head on the OE KF pump body would add some variables to the equation and needing to tweak a bit.  I'll be creating a little chart to keep track of any changes I make to the settings and mark them so I can methodically work through them.   And yeah, I think the 02 sensor is a must, not a luxury on these cars.  I am going to keep posting my approach, changes and results so I can add back a little to the forums.  

The original cylinder head in my tii has been shaved to minimum thickness and I’m running 2nd oversized pistons.  Stock refurbished KF pump was sent to Fairchild and I installed a set of newer injectors. I had to do lots of tweaking to get my car running better.  My part throttle hesitation and lean points were mostly cured by a new return spring for the D cam (the tiny one inside the throttle body) and a rebuilt/recurved distributor.

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