Elusive F/I Problem Persists

[Sportwagon75]

Well...I thought I had this elusive little problem solved. But we took the Manta for a whirlwind trip from Virginia to New England over the weekend and the problem persists. The car performed almost flawlessly for 9-1/2 hours each way with the A/C running full blast all weekend. However...when the car has been running at highway speeds in hot weather for 3 or 4 hours, it starts to sputter and lose power. These are the same symptoms I encountered on the return trip from Carlisle. Take it out of gear, shut off the ignition, coast for 100 yards or so, turn the ignition back on, dump the clutch...and the problem is gone for another 5 or 10 miles. Once the sun went down and temperature gauge came down abit...the problem vanished. It also seems to be worse when the fuel tank is low. To give an accurate decsription...if you've ever experienced a point gap that slowly closes up at highway speed...then you know what this feels like. Clipping along fine at 70 and then you try to accelerate up a hill and you get severe hesitation, sputtering and a slow but gradual loss of power. Someone suggested that it sounded like a condensor that was going bad. So I replaced the condensor before we left. Next thing I'll do is install the Pertronix but I still have a feeling that this problem is somewhere else. After the Pertronix goes in, I'm planning a fuel pressure regulator replacement. If that doesn't do it...then I'm looking to the MAF. Does anyone have any other suggestions or insight into this problem?? I've become pretty good at diagnosing 1975 F/I problems but this one has me scratching my head. -SD

PS - The tank is clean. Pickup sock, fuel pump & filters are all new.

[RallyBob]

I wonder if this is a general electrical issue? Have you checked all grounds, output voltage, etc? Low voltage will wreak havoc with pump volume/pressure, air flow meter readings, resistance at the injectors, etc.

Bob

[Sportwagon75]

Bob - That's why I call it "elusive"!! All the grounds are good and I've checked voltages at the dual relay, injectors and fuel pump and they're all good. (when I check them) Problem is...without hard wiring a meter to the dash, I can't see the voltages when the problem arises...and it's only an occasional problem. Perhaps that's what I need to do. I'd also like to see fuel pressure at the dash too. Maybe that'll be my weekend project!!

[Paul]

Have you checked the fuel sock in the tank? Could a piece of trash get sucked to it and when you shut the engine off it releases from the sock only to have it sucked back a few miles later?

Paul

[Sportwagon75]

Paul - As I mentioned in my original post...the tank, sock and filters are all clean and new. The problem is somehow related to outside temperature as it never appears when the weather is more moderate. Over the weekend it rained several times and cooled things off. While it was raining (and after the sun went down)...the problem went away. -SD

[Paul]

Sorry, my mind wondered off before I got to the bottom of the post. Temperature being an issue would tend to point to a break down in an insulator somewhere. However, your temporary cure, on the surface anyway, doesn't seem to point towards electrical/thermal problem. But, it probably is.

What is this? Stump the Band?
Paul

[tekenaar]

Originally Posted by Sportwagon75 Well...I thought I had this elusive little problem solved. . . . Does anyone have any other suggestions or insight into this problem?? I've become pretty good at diagnosing 1975 F/I problems but this one has me scratching my head. -SD PS - The tank is clean. Pickup sock, fuel pump & filters are all new.

My only question is: You talk about a fuel "sock" ('75 tank and fuel pickup, right?) and that it's new . . . you did this personally or watched someone do it with a new, in the box NOS part, right? So, where did you find an NOS in-tank filter or was your filter merely "cleaned"? I'm NOT trying to be a smart-ass here, just trying to get the facts straight. It makes a BIG difference.

The '75 in-tank "sock" is really more like a very fine meshed metal screen filter than an actual sock over the tank pickup pipe. This IS a replaceable element about 1.9375" dia. x 2.1875" long with a 3/8" hole in the center at one end that slides over the pickup tube, which you already know if you replaced it. Sorry for any repetition here.

I have NOT found a way to reliably "clean" this filter and the mesh is SO fine that if there is the slightest trace of anything in the tank other than gas, the "used, cleaned" filter will clog up again very quickly, at least to the point where it will exhibit the EXACT symptoms you describe.

FI fuel pumps are designed as pressure pumps and their performance and that of the FI system it feeds degrades rapidly if you restrict the input fuel flow in ANY way.

MAYBE one other thing to look at . . . have you checked your return line for flow restrictions? A kink or restriction in your return line and it acts like a pressure regulator by not allowing unimpeded gas flow back to the tank.

[Sportwagon75]

Otto - I appreciate your knowledge and experience. Your input and suggestions are always welcomed. Unfortunately, this mystery remains unsolved. Having numerous 75's through the years, and presently with 4, I'm pretty familiar with the unique parts of these Opels. The fuel "sock" is pretty much a generic expression in my mind for lack of a better term as it relates to the 75. It's more of a fuel pickup "can" and yes it is, indeed, new. This was a tank that I personally cleaned. It looks brand new inside. Secondly...it's a rare occasion when an NOS fuel pickup appears on Ebay. Even more rare when it's for a 75. So, naturally, I responded rather aggressively when one turned up a few months back. (there's a member here who can bear witness to my aggressiveness in acquiring it) So anyway...all fuel lines were cleaned out and all rubber hoses were replaced. The injectors were cleaned and the NOS pickup/sender was installed. Once again…even if the sock/can were not new…the symptoms would be more universal if it were a plugged screen. This is clearly a temperature-related problem that disappears when the weather is cooler. Lastly…regarding your suggestion of a restriction in the fuel return: If this were the case…it would tend to create back pressure at the injectors and consequently force more fuel to the injectors rather than less. Return flow back to the tank is not my problem…rather it’s flow to the injectors that “appears” to be the problem. In fact…several years ago I had a 75 that was running real rough and I suspected a faulty pressure regulator. To check my suspicion…I pinched the fuel line at the tank return and the engine roared back to life and ran perfectly. Replaced the regulator and went on my merry way. So anyway...I appreciate your suggestions but I guess I'll have to keep looking. When I track it down...I'll let you know where it was. -SD

[GoinManta]

Well here is a shot in the dark.

The Aux. Air Valve? It is bolted to the Thermostat housing and possibly gets screwy when it gets too hot?

Also where is the fuel filter? As Otto pointed out on my Manta, the metal Fuel Filter next to the exhaust manifold could cause vapor lock.

One other thing.. Fuel Pressure Regulator is it new ? Possibly its getting too hot and acting screwy because of it..

Although you probably already have checked them, if you hadn't just figured I would mention them.

Charles

[GTJIM]

Cutting out after starting was traked down to low fuel pressure on my Isuzu Impulse. The fuel pump was old and getting tired. The car would cut out on the move, as soon as the air temperature rose about 20 C.
So make sure both the fuel pump and the fuel pressure regulator are allowing the correct pressure to be maintained in the fuel rail.

[davegt27]

ever see that problem where the FI screen at the injector gets partially clogged

you pull the injector off and tap the hose end on the ground and all kinds of junk comes out

75 FI and can be a screwy beast every thing from cracked sprint header(did i mention the sprint headers crack sometimes) to the wiring to the fuel pump, to thermo time switch, to fuel lines closing off when getting warm

also bad ECU's cause problems not to mention fuel filters and dual relays

the starter has been know to cause 75 FI problems

if you can get a hold of a Glen's repair manual for the Opel it has a real good TS section on the 75 FI

also How to tune & Modify Bosch FI by Ben Watson is real good

speaking of Carlisle i was watching a Video from Opels Unlimited about a month ago where this Guy Todd goes to Carlisle and fixes all finds of Opel problems
i am talking some weird ShxT

as i was watching i sat there thinking you can avoid a lot of weird problems by not running the car forever on old parts what i mean is people try to get 2 years out of a set of spark plugs or points or have 5 year old spark plug wires never change there fuel filter the coil is 30 years old

Sportwagon75 i know you know all this anyone that's had 75 FI has to be able to Troubleshoot i am just saying this for other peoples benefit

i solved a lot of my 75 FI problems with new injectors
there was one problem where the guts of the Aux air valve would blow out the back of the Aux air valve (elect part)

the biggest weirdest 75 FI problem has to do with power to the FI pump
you will see a lot of 75 cars with a new 12v wire running straight to the fuel pump (people would give up trying to figure out why the have 12v at the fuse and no power at the pump and just run a new wire)

anyway your at the point where you start replacing parts.
good luck
Davegt27

[Sportwagon75]

I appreciate everyone's input. I think I'm going to use a process of elimination since this is an intermittant problem. I'm going to start by installing the Pertonix that I've already purchased. Then I want to get a fuel pressure indicator at the dash so I can monitor pressure when the problem arises. I think Bob's suggestion is also a good one...so I think I may also run some temporary wires to a couple places and put a VOM on the dash to watch what's happening. Dave is right about the TS section of the factory service manual for 75. It's a very good TS guide. I have one and have used it a number of times to track down problems. All the fuel injectors were cleaned (and even reverse flowed to clean the screens). The fuel pump is new and the fuel filter is in the stock location. (at the tank) I had not considered the Aux Air valve and that could be a possibility since it's a temperature sensitive device. My guess is that it's a sticky pressure regulator, the aux air valve, or a problem with the MAF. Whatever the case...I will post the answer once I've tracked it down. Thanks again Y'all !!!

[Gary]

Originally Posted by Sportwagon75 .... Then I want to get a fuel pressure indicator at the dash so I can monitor pressure when the problem arises.

Let us know what you end up using for a fuel pressure gauge. I started to look for one for the Senator.

If you want to put it in the dash, be sure to get one with a remote sender. (Don't want a pressurized fuel line in the passenger compartment)

[davegt27]

i used to tie wrap a press gage to the windshield wiper ha ha autometer has a new gauge setup but its big big bucks

i thought the Glens repair manual was better then the factory but that's just me

if i where to guess i would say you got the wired Fuel Pump voltage problem

when you take the plug off the fuel pump the voltage is fine but after awhile it goes down or completely away

now is a good time to update stuff i wouldn't goof around with cleaning injectors all they do is run fluid threw them just get some new ones

Buggy warehouse (or a bug shop will be cheaper) 914 second design is what i would go for

anything on the car over 20 years old that can be unbolted and replaced just get a new one if you can

dual relays used to be $45 at a bug shop the other FI stuff you will have to keep

coil get a new one check the resistor wire

go to the starter make sure its connected right or just get a new starter solenoid

good luck
Davegt27

[Sportwagon75]

"Don't want a pressurized fuel line in the passenger compartment"

Actually...I have a spare oil pressure sender from another 75 wagon with Rallye gauges. The pressure range is similar (I think the oil pressure gauge goes to 60) so I thought I'd use that and temporarily send the fuel pressure reading to the oil pressure gauge. Should work fine for short term use!!!

[Dmccollam]

Scott,

Check the fuel pressure and the reponse when you "blip" the throttle at idle. If you don't have at least 32-36 PSI at idle and get a significant change in pressure, the fuel strainer could be blocked. If the pressure is not above 20-25 PSI, the pump or the regulator could be bad. I'd also change the coil when you go to the Pertronix, making certain that you have the "gap" correct on the Pertronix pickup.

I also have a Bosch FI troubleshooting guide that has a schedule of items to check in order based upon the symptoms. Let me know if you need me to send a copy.

Good luck.

Dave

[gtzero]

Originally Posted by Dmccollam Scott, Check the fuel pressure and the reponse when you "blip" the throttle at idle. If you don't have at least 32-36 PSI at idle and get a significant change in pressure, the fuel strainer could be blocked. If the pressure is not above 20-25 PSI, the pump or the regulator could be bad. I'd also change the coil when you go to the Pertronix, making certain that you have the "gap" correct on the Pertronix pickup. I also have a Bosch FI troubleshooting guide that has a schedule of items to check in order based upon the symptoms. Let me know if you need me to send a copy. Good luck. Dave

Dave, I may be in need of the FI troubleshooting guide. I'm getting all of the symptoms listed in this thread. But my problems don't have to wait for things to warm up. In fact, the loss of power was so bad that I had to get flat-bedded last night. The shop has just informed me that the fuel pressure is good at 35psi. I thought almost for sure that the problem was in the fuel system. But the mystery continues.

Manny

[houserc]

Has this been resolved yet?

[DennisGardiner]

Considering you have a power loss when HOT, and you eliminate the
problem after shutting the engine down. Along with a power loss when
climbing hills....

I would say, (without being there & having a pressure gauge hooked to
your engine while running to verify), I would say you are loosing fuel
pressure, when hot.
I personally would hook a 60-80 psi gauge into the fuel line from the
cold start valve & tape it to the windshield pulling the hose through the
hood. Then see if there is a pressure drop when you get the hesitation.
IF YOU DO, you have eliminated the computer, air flow meter, injectors,
cold start valve, thermo-time switch, and ignition system from the equasion.

Then you can redouble your efforts to see if the fuel pump relay is weak,
gets HOT, or there is another issue, like a bad regulator.

On my personal EFI GT, when my car lost power, was pressure related.
Note: Opel 75 EFI runs between 31 psi under (in gear deceleration) &
44 psi under WOT (wide open throttle).
Note: #2 2.0L EFI runs at slightly lower pressures.

Dennis 73 GT & 73 Manta both EFI


...when the car has been running at highway speeds in hot weather for 3 or 4 hours, it starts to sputter and lose power....
...Take it out of gear, shut off the ignition, coast for 100 yards or so, turn the ignition back on, dump the clutch...and the problem is gone for another 5 or 10 miles.....
....Once the sun went down and temperature gauge came down abit...the problem vanished.....
....It also seems to be worse when the fuel tank is low.....
...try to accelerate up a hill and you get severe hesitation, sputtering and a slow but gradual loss of power....

[gtzero]

Originally Posted by houserc Has this been resolved yet?

I was trying to find some info on fixing my fuel leak when I stumbled upon this thread. And unfortunately, it sounded a lot like what happened to me last night. With the exception of having to have things get hot. I had problems right from the start up.

Manny

[Sportwagon75]

Originally Posted by houserc Has this been resolved yet?

I'm still eliminating possibilities. Does NOT appear to be ignition related thus far. As stated...since it's an intermittant problem, it's harder to track down. On top of that...this summer has been extremely busy for me and I've spent the last couple months since Carlisle running like a headless chicken. Spare time has been in short supply and the car runs fine for short hops. The problem only appears over long hauls on hot days. I'll post the solution when I find it. -SD

[MantAscona]

Hi Scott,
I was figuring it was a coil related problem as I have seen on customer cars many times and have even experienced on my own vehicle once. Another thought is the fuel pump relay as was mentioned by another member. My wifes Honda Accord was acting almost the same way. When the weather was hot the and the windows were up the car would not start or would quit running. However, when the weather was cooler or the windows were down the problem did not exist. It drove me crazy for awhile trying to figure out what exactly the windows being up or down had to do with it. This was the only variable that had an affect on whether it would run or not. I finally pulled the fuel pump relay from under the dash after determining that it would cut the fuel off when this happened. I opened the case of the relay to check it and looked at it with a magnifying glass. I found a cracked solder joint on the circuit board, resoldered it and never had the problem again. What would happen was the interior temperature of the car would reach a point where the gap in the solder joint would expand and break the circuit to stop the pump. When the windows were down it would cool enough to close the gap and complete the circuit to make the pump run again. About 10 months after all of this my shop received a tech bulletin that this exact thing was happening in enough cars that Honda was replacing the relays for free as a courtesy to the customers. Don't know if it's your problem but, it's worth a look. I would also still check the coil. Good luck!

Duane

[gtzero]

Duane, that was a cool bit of detective work.

My problem has been solved. My car just needed it's MAS unit tweaked. I guess when I replaced my headers with the manifold, something got fouled up. Anyway, I think I'm back on the road. I'll pick up the car tonight and see if she's back in tip-top condition.

Manny

[davegt27]

some other items to look at on the 75 FI is the starter solenoid

yeah starter solenoid on the 75 starter there two prongs and one is used to power the FI system

this can cause intermittent problems with the FI system kinda like a coil that brakes down with heat or vibration

might be a good idea to use a Otto Start type setup for the FI system

another place is the dual relay one time i had some small jumpers from Radio Shack to make one work

keep us posted on your progress

oh i forgot every time i checked fuel pressure it was always around 42psi
but my system was on a GT where i used one of the vents in the 72 GT fuel tank as a return port

the fuel vent on the GT gas tank was drilled out so there was no restriction except for the size

the deceleration device was tossed


Davegt27