Help with Fuel Injection/RPM issue, A/V included

[Jason Marshall]

All,
Sorry for the long post, but I've done alot already based on searches and advice on this forum, and I want to be comprehensive so as to avoid replies asking "did you do this?"
Long description and links to youtube videos at the end for your review.

SUMMARY OF ISSUE: '74, 18.L, L-Jet. Car will start and idle fine, after warm it will fall back to idle once you get above about 3000rpm.

HISTORY: Purchased car 10 years ago from very knowledgeable teener. (I drove it 7 hours home the day I bought it!) Drove it every weekend in nice weather, no problems. Very few mods, none to engine area. Performed routine maintenance and fixed small issues (sloppy shifter, bushings, etc.) Three years ago had a fender-bender damaging the right fender, bumper and bumper pad, but still ran and drove fine. Took it to high-end body shop in Dallas. (Hagerty's Insurance is great, they had no problem cutting a big check.) Body shop had a hard time finding parts, so it was with them for 4.5 months--in the depths of an extremely hot summer, if that matters. Went to pick it up, looked fantastic, but shop owner said "yeah, well, sorry but it's not running so good now." He was right. Towed it to my garage.

914 would start and idle, but after warm, when throttled up to about 3000-3500 it would suddenly drop back to idle. Didn't die, but same thing over and over. At the time, checked AAV, Ignition, Spark, Fuel Pump was running, etc to no avail. Didn't have a fuel pressure gauge at the time, and I suspected bad fuel pump. A new house and a new project (72 Bronco barn find) came along so the 914 took a 2.5 year nap in the garage. Turned my attention back to it about a month ago.

WHAT I'VE DONE: First, drained tank, new gas and battery, just to see if it would start. Nope. At this point I decided to treat it as a car that had sat for ten years, not 3. Here we go, with help from searches on this forum.
1. Suspected fuel pump. Took a while but found a used one on this forum. (3 prong in original location.) Took mine off car and bench tested flow on both. Both good flow. Installed in-line fuel pressure gauge. With jumper (engine off) to fuel pump, get good 40 psi.
2. Replaced all suspect fuel lines with new lines, including all lines under car. (One line seemed kinked....could this be it? As you will see, no.) New fuel filter.
3. Replaced all vacuum hoses except the large one that goes to oil filler...can't seem to find one. But it seems fine with clamps. Inspected S-Boot for any cracks, and none. (Some hose were toast...could this be it? No, as you will see.)
4. New spark plugs, wires, cap and rotor.
5. Cleaned, sanded and re-installed ground strap. New neg. battery cable, and added extra ground from terminal to tins.
6. Cleaned all contacts and plugs using spray contact cleaner. Triple-checked all connections. (so many stories here of forgetting to re-hook AFM plug!)
7. Performed Bowlsby 22 step fuel pump test/checklist. Passed.
8. Performed dual-relay test using 9-volt battery. Passed.
9. Turn key on, push AFM flap, fuel pump runs.

MOMENT OF TRUTH: Took a deep breath. Started right up and idled fine. Let it purr a little bit at idle to warm up. Jabbed the throttle a few times and revs seem great...BUT, once it got warmed up, same old story. Once warm, it idles fine, but falls back to idle when you get above 3000 rpm. Checked timing, it was a bit retarded, and advance made idle better, but didn't solve problem.
Fuel pressure when all warmed up is now running at 30 psi, and dropping down to 25 briefly when you try to rev it. Not good.

So, this is the point where I'm asking for help!

My only guesses:
1. Bad Fuel Pressure Regulator (I didn't think these went bad often).
2. Fuel pump and filter getting hot? They are located not too far from heat x-changers, and they get warm to the touch, but by no means "hot." Also, I'm not suffering any vapor lock when I go to restart the car, even when hot it fires right up.
3. ECU or AFM issue? I hope not.

I can't invite all of you to my garage so I made two videos, youtube links below. One video is test using fuel pump with a switch jumper to battery. One is the fuel pump plugged in as it should be. (I mention "oil pressure" at the end of one video, but clearly meant fuel.)

Please digest and dissect. Any and all comments and suggestions are appreciated, thank you in advance. I will be back at my garage tomorrow morning for more!
Jason

https://www.youtube.com/watch?v=UFoErHeh07Q

https://www.youtube.com/watch?v=Kyu6duP-6f4

[BoxsterGT]

You mention draining the tank and putting in fresh gas, but you do not mention dropping the sock filter at the bottom of the tank.

If this gets clogged with fine rust particles it will allow only a limited amount of fuel flow. Sometimes enough to idle down the road but not enough for a sustained run over 3k rpm.

BTDT.

Len

[Jason Marshall]

I have not, will check today!
(Can I check that by removing the filler and/or sender assembly and using a flashlight? If it need replacement, do I have to pull the tank?)
Thank, Jason

[Jason Marshall]

Thanks, answered my own question with some research.

http://c767504.r4.cf2.rackcdn.com/201-00.gif

Jason

[Jason Marshall]

All,
Well, got back in the garage today to perform some more suggested tests. I'm posting the results, but still have no solution. However, some interesting results regarding fuel pressure regulator (FPR.) (Pic and video link below). Still have the problem: rpm fall-off back to idle one you rev to about 3000 rpm.

So, in addition to the nine (9) tests performed as mention in my original post, here is what I did further today:

10. Easiest test first, I ran the car with gas cap removed, in case vacuum was building in tank due to kinked line. No, change to bad behavior. Also, look at all the vent lines and none are kinked. (In fact, all my emissions stuff is gone, so the tank vent line ends open in the engine bay.)

11. Next, took off gas filler and sending unit to take a look inside gas tank. Inside of tank and sock filter don't look too bad. Pic below. The filter does not look corroded like others I've seen on this forum. (The "junk" you can see at the bottom of my tank is not rust on the tank, but is loose particles, dirt, rust chips, etc.) The sender unit was spotless.

12. On to suggestion about disconnecting the FPR vacuum line to see what happens. Disconnected FPR vacuum line, plugged the T to prevent vacuum leak. Car started and idled, but same issue with drop off at 3K RPM. INTERESTING PART: with the FPR unhooked, the fuel pressure says steady at 39 psi, no matter revving. If you recall, when it is hooked up the psi is about 30 when running and drops down when you rev RPM. Seems to be opposite of what the FPR should do, correct? See video.

13. Finally, I had some time so I decided to eliminate any concern regarding the fuel tank or any lines between the tank and the firewall. So, I fab'd up a "tank bypass". Basically, a small container of gas with the fuel pump inlet and fuel return lines in it. Ran the car on this setup. No change. My Youtube video link below shows this setup, as well as how the fuel pressure reacts to removing FPR vac hose.

So, bad FPR? Hard to say but those test results seem odd. Hate to just start throwing parts at the problem. Plus, while searching around I found a post by a guy with a similar problem, and similar readings, and a new FPR did not fix. Link is not this forum, but here it is in case you're curious:
1975 914 with L-Jet: Problem and questions... - Shoptalkforums.com

I plan to grab some "noids" tomorrow to test FI's, just for the heck of it. Also, I think I can check vacuum pressure with my vacuum tool, just need to read instructions. (What should vacuum be at idle? I think my vacuum is good...car dies when I remove Oil Cap, and tries to die when I remove even a small line. All vacuum lines are new.)

ANY THOUGHTS OR SUGGESTION ARE GREATLY APPRECIATED!!!!
see pic of tank and youtube link below.
Thanks, Jason

https://youtu.be/irhv2wVpYLg

[Dave at Pelican Parts]

Debris in the tank isn't good, but that's a pretty darned small amount of trash down there. (Hint: Don't use a shop-vac to get the debris out! No, I haven't done it myself, but I have read stories...)

Does your fuel pressure drop when the engine dies back to idle?

Is the throttle still open when the engine dies back to idle?

The FPR is, from what I have read, supposed to keep a constant pressure across the fuel injector. So when the pressure in the manifold is low (throttle closed) the fuel pressure should be lower. When the manifold pressure is higher (throttle open) the fuel pressure should rise. With the vacuum connection unhooked, there would be no change in (detected) manifold pressure so no change in fuel pressure. Note that throttle position is not the sole determinant of manifold vacuum; engine RPM also affects it, and possibly other things.

But it does sound kind of like your FPR is working the opposite of how I think it is supposed to work. I cannot easily see a simple failure mode that causes that behavior, though, so either there is a manufacturing error in the FPR, or my understanding is wrong, or something I am not seeing is going on.

--DD

[Jason Marshall]

Dave,
Thanks for the reply. Starting with your comments about the FPR first, as you can see in the last video I posted, if the FPR is hooked up to vacuum, the fuel pressure sits around 30psi, and will drop a bit when revved and then settle back to about 30. With the FPR unhooked from vacuum, the pressure stays steady at about 39psi, which is what you would expect because if the FPR is unhooked it should just stay wide open.

In either case, once the rpms drop back down to idle the pressure stays at the values mentioned above.

Next, yes, the throttle is still open when it dies back to idle. In the videos, I am opening the throttle up, and at about 3000 rpm--without releasing throttle--the rpms just drop back down to idle.

As odd as the FPR behavior seems, I really don't think it is a fuel delivery problem at this point, based on all my previous tests. Based on feedback, turning to ignition.

Since my last post I have also done the following tests based on feedback, but with no improvement:

14. Checked if timing light cut out when I revved the engine. Nope. Checked all four wires and get good strobe at idle, and when I rev it, and even when it falls back to idle by itself, the entire time I have good strobe.

15. Installed new Bosch blue coil.. No change.

16. I was curious about vacuum. Vacuum at idle flutters at 10-12 psi. (approx. 800-900 rpm idle). Rev it as much as I can and vacuum drops briefly then shoots up to 15-20...(then my symtom causes it to fall back to idle.) Not sure what vacuum level should be, let me know if this sounds within normal parameters.

17. Did injector noid light check, looks good. (Couldn't get #3 connector off, but have no reason to think that would be the problem. 1,2,4 all "blinked" fine.)

Tomorrow am checking dwell and timing. Was waiting on dwell meter to come in.
Otherwise, still at a loss.

Any thoughts appreciated.
Thanks again,
Jason

[mark 74 carrera]

What if your centrifugal spring in the distributor cap is broken or worn out? Your engine sounds a little like the cut out that happens at redline. It does sound like an ignition problem to me.

Mark