MFI car help (long)

[TargaT]

Hello Friends,
I'm struggling to get my 73T 2.4 running properly. I'm looking for some suggestions. Here's my story.
Freshly home rebuilt stock 2.4 (no leaks). Got everything sorted to the best of my abilities. Running reasonably well. Then took it to a shop for final tweeking. This guy has been around a for a number of years and has a relatively good knowledge of MFI.
Here's what he found. Two collapsed tensionsers (that I had rebuilt)- replaced with turbo units now. Cam timing off on one side and some of my rocker clearances were off.
The car came home running great. Got a couple hundred miles on the car in short trips in the area and the car still ran great (about a week), the started planning my trip to Watkins Glen for the vintage festival the following weekend. Left on my trip and stopped at the border about an hour into the trip, as I pulled away the car stumbled and got worse from there. Losing power and bucking. Cont'd

[TargaT]

. Stopped at the service centre about half an hour later. I had a new set of plugs (BP7ES), figured the break in plugs were bad and they were not correct (R6). Changed the plugs, fired right up and came back to life.
Ran great for about another hour until I stopped at the next toll booth. As I pulled away the same problem. Continued to drive the next 2 hours with reduced power just to get to our hotel. Also the temp was getting dangerously high as we pulled off of our exit. As we pulled off the car completely died and would not restart. The fuel was kind of low so I immediatly thought crud in the tank. Went and got a container of gas poured it in gave the car a good shake. Fired right up and ran fine to our hotel about a mile away.
So clearly we had to find a shop in the morning that would drain the tank and clean out the screen to be ready in time for the "Tour de Marque" for 10:30, even though I had previously done this myself.

[TargaT]

The shop did find some very minor particles along with what appeared to be water droplets. Car fired right up and came back to life. Raced to meet with the group, arrived at 10:29 and they had left 10 minutes ago. Took off to try and catch up, 10 minutes later the problem started over with about a 45 minute drive to the Glen. The car got worse and worse and actually coasted into our campsite as the car stalled dead, again the car got dangerously hot. Seemed obvious, fuel starvation making it run lean and hot. Let the car cool down and fired it up 5 minutes before track time. Again fired up and drove fine. Made it to the gate just as they closed it and waved me off- too late. Frustrated I parked the car the rest of the day and went downtown with my pals to take in the festival. Went to the paddock Saturday to talk to some wrenches and get some opinions. The conclusion came back that it was the electric pump. Scoured the paddock but could not find a spare. Decided to make an early departure Saturday afternoon, not knowing how long it would take to get home. At this point the car was running at about 60% power but did not get overly hot. I kept the RPMs down and the air temp was lower. Made all the way home this way without a hitch. Checked to see how the pump felt- not hot and sounded OK. cont'd

[TargaT]

Finally pulled my plugs, all black. Sure doesn't look like fuel starvation now. Gave em a good cleaning and reinstalled. Car is still the same low on power. Did a diagnostic of the MFI pump thermostat and it is working perfect. Checked the cold start prime and no leakage. Next plan to do a fuel pressure test and looking for other suggestions.

Other info:
Almost everything has been replaced. New injectors, fuel filter, all soft fuel lines. MFI pump has been cleaned and inspected by a local diesel shop. Electric pump is original.
Wrench who did the final tuning on the car indicated he had trouble adjusting the pump. He pulled the adjuster screw and said there was some evidence of grit in the pump. What are my next steps?

Thanks, a frustrated MFI guy who had a taste of how good it can be.

Joe

[nabilious]

Stupid question maybe, but how does the fan belt feel and look? Also the hot air pipe from the heat exchanger to the pump? I understand all of the symptoms that you describe but the fact that it gets hot too throws a proverbial wrench into the fuel starvation theory. I can;t imagine that it runs lean enough to make it run that hot when your not on the track or something like that. For good measure, wouldn't hurt to hook up a fuel pressure gauge inbetween the fuel filter and the MFI pump....just to make sure of things. Report your findings!!

Nabil

[TargaT]

thanks, fan belt is new as is are all the MFI hoses. What should the fuel pressure be at that point?
Joe

[nabilious]

I don't have the correct books in the house to tell you that but one idea is to check it in the first 15 minutes when its running good and once it goes it to sh&t to check it then too. see if it falls off some. Its a bit of a trial and error but I guess you have to become intimate with the system....unless one of the veterans (Henry Schmit, Grady Clay...you guys listening?) chimes in!
Nabil

[jstobo]

The MFI electric fuel pump should put out 1 Bar or 14.5 PSI. The MFI Pump puts up the rest of the pressure for the injectors.

[jluetjen]

Distributor advance/retard mechanism -- is it sticky? If your timing is off, the plugs can foul and the temperature can go up .

[Zeke]

A simple check: The MFI drive belt timing. We had a T Sporto that behaved like this and it was several teeth off due to the belt having been worn almost smooth. Ran better when it was cold.

[Rot 911]

Too add to what the others have said. Spend some money and get a Gunson gas tester. Relatively cheap and it takes the guess work out of wondering if your fuel mixture is too lean or too rich. You can make adjustments and instantly know what the affect is.

[Grady Clay]

Bump

I'll work on this in the morning. I'm too goofy from stupid meds right now.

Best,
Grady

[Grady Clay]

TargaT,

The fact that the condition changes back and forth is both an advantage and disadvantage. We don’t want the problem to simply disappear for some unknown reason only to reappear at some inopportune time. Let’s start with the least disturbing tests first.

Ignition timing is an easy test and you can drive with the timing light in place. You want to look at the steadiness of the timing, the repeatability up & down of the advance curve, etc. A dwell meter could also be installed to see if the points change.

Double check that the fuel lines are plumbed correctly at the fuel filter console. Porsche published an incorrect diagram early in MFI history. Check HERE.

Given the situation where the fuel pressure is suspect, you can plumb a temporary fuel pressure gauge. Safety is your prime concern. Fuel pressure is measured at the fuel filter console banjo fitting closest to the rear of the car. It is easy to install a “T” fitting in that hose and run a measuring hose to a fuel pressure gauge in the cockpit. Run the hose out the back of the engine compartment and tape it to the side of the rear window and in your open door window. Use real fuel hose and clamps at every connection. Don’t tolerate any leaks. Even the slightest fuel leak can lead to disaster. Make the hose long enough to easily reach the fuel filler on the LF fender as you may want to also use it for fuel flow testing.

The minimum fuel pressure spec is 0.8 ±0.2 bar (11.8 ±3.0 psi). Under normal operating conditions the fuel is returned to the tank by the over-flow valve (in the middle fitting on the fuel filter console) and the fuel pressure is about 1.0 bar (14 psi). The running pressure is not critical, only the minimum pressure.

You can use a flashlight and mirror to inspect the MFI pump timing belt. Milt is correct; the belt teeth can quickly fail from misalignment or too much tension. Changing pump timing can be frustrating to diagnose.

Please report your findings.

Congratulations on your rebuild. These are minor (yet frustrating) gremlins that will get sorted out. Once running correctly all the time you will want to do a through set of CMA checks and adjustments. This will both get the MFI adjusted the best possible and establish your baseline for future troubleshooting. A complete and extended CMA is part of your regular maintenance.

Best,
Grady

[TargaT]

OK my fellow techies, I finally got some time to get back at it.
- Checked the dwell- bang on at 38
- timing was slightly off about 3 deg- corrected it and throttle response improved (why did it change?)
- checked MFI pump alignment- right on
Drove the car and it was still really flat on power probably running at about 70% power level. Cylinder #3 popping badly through the intake.
Went out and bought a compression gauge and did a test this morning. The numbers are low but were based on a stone cold motor and and a hose fitting put in finger tight only, so I think they are OK.

The right bank 6,5 and 4 were all pretty consistent at about 120 and seem OK to me?

The left side performed differently: cylinders 1 and 2 eventually made it up to 120 but required a lot more cranking. Cylinder 3 initially sat at 90 for a number of cranks then eventually made it up to 110 and peaked.
What does all this mean? Has the cam timing on the left side gone off again? Have I lost another chain tensioner? A sticky number 3 valve or have all the clearances gone off again? What are my next steps.

Still haven't performed the fuel pressure test that I wanted to do but this certainly looks to be secondary at this point. Any suggestions we be greatly appreciated.

Joe Dren

[Grady Clay]

Joe,

At this point I would check the cam timing. All you have to do is remove the intake covers. The specs are 2.4 to 2.8 mm lift at TDC Overlap. Remember to check/set the valve clearance. (Make sure there aren’t any broken rocker arms.)

The other test that may yield some useful information is a cylinder leak test. Our host sells the tool.

Have you compared L/R air flow at fast idle?

Best,
Grady

[David E. Clark]

This sounds to me like there may be two problems that are simultaneously affecting your car. Since we are all just guessing at this point, you’d probably be best to start off with the easy tests:

1)

The shop did find some very minor particles along with what appeared to be water droplets.

These “minor particles” have a way of accumulating until they become a major nuisance. You might consider replacing the fuel filter element since this can lead to misfiring and fuel starvation. You might also want to run some techron through the system since it sounds like you might not only have dirty fuel but also old fuel which tends to gum up the injection system.

2)

Finally pulled my plugs, all black.

Have you checked the CO adjustment with an exhaust gas analyzer? Black plugs means you are running too rich – duh! There is really no easy fix here. You need to run through CMA. Get a copy here.

Finally, make certain that the throttle valves are synchronized at 3,000 rpm. Varying degrees of air intake can lead to all sorts of misfiring and poor running.

Good luck.

[TargaT]

OK, so I have it running fine when cold. As the car heats up it begins to run very poorly. What I have discovered is that as it heats up the timing begins to retard. The problem begins at about 200 deg and becomes really bad as it approaches 210. At this temp it retards about 5 degrees at idle. What controls the timing? and what could I check next? So it appears the retarded timing is causing the engine to heat up? This takes about 20 minutes of spirited driving.

Thanks, Joe

[Grady Clay]

Great.

Sounds like we have a pretty clear symptom for the diagnosis.
Based on this it is a distributor problem.

My recommendation is to position the engine at Top Dead
Center (TDC) Compression (where the rotor is pointing to
#1 cylinder). You can now remove the distributor and then
(later) re-install it in the same position.

Take the distributor to a local “auto electric” shop that has
a Sun distributor machine. The problem is the advance
mechanism is sticking and not free to move through the
advance curve. The cure is to free-up the mechanism.


After you have everything in the distributor functioning
correctly, you should document the actual advance curve
and compare it to the Porsche specification below.
"
"
© Dr. Ing. h.c. F. Porsche A.G.
"
"
© Dr. Ing. h.c. F. Porsche A.G.

If out of specification, the shop should be able to help you
correct it. If not, post here and we can lead you (them)
through the process.

Best,
Grady

[shbop]

Just curious. Were your heads and chain boxes milled during re-build?

[TargaT]

Grady, thanks for the confirmation. That was my next step. Another suspect to me was the CDI unit, do these ever behave this way? I felt it and it was very hot. I was thinking of getting some cold spray to see if it has any effect, but I will get the distributor checked out first. Another question, what is the middle fuse in the rear electrical panel? and why is there a wire only on one side? Am I missing something.

Jon, to answer your question, the heads were surfaced slightly but were compensated by using the apppropriate thickness gaskets.

Thanks, Joe