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'76 2.0L won't stay running
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sixer
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PostPosted: Sun Feb 15, 2015 2:58 pm    Post subject: '76 2.0L won't stay running Reply with quote

Hi all,

First off, I've got a 1976 2.0L engine, with stock fuel injection. We recently dropped the engine and transmission to clean off many, many years of oil leak accumulation and replace the suspected seals behind it. It ran just fine before we dropped it, but now that it's back installed we're having trouble keeping it running.

Symptoms: starts fine and idles fine until warmed up, then dies and won't stay running. Unplugging the AFM allows the engine to idle quite well even when warmed up.

Troubleshooting done so far: checked 14 times that everything is hooked up as before the engine drop, both vacuum lines and electrical connections. Ran an unlit propane torch around trying to find vacuum leaks. Nothing notable there, so I sprayed all connections with water to the same effect. All vacuum lines have been replaced, s-boot and other items inspected for cracks and leaks, etc. Googled and read countless threads on the samba, trying to figure out what to do next. Also checked TS2 sensor, it seems to fall within the specs listed in the AFC fuel injection guide.

So, now what should I do? I'll be picking up a fuel pressure gauge later tonight to facilitate troubleshooting further. I'm trying to get a plan together for when I can get back to the garage to solve this as soon as possible. Thanks all!
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Last edited by sixer on Sun Feb 15, 2015 3:38 pm; edited 1 time in total
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EZ Gruv
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PostPosted: Sun Feb 15, 2015 3:33 pm    Post subject: Reply with quote

Last time I dropped/installed my engine, the fuel pump died when I tried to start it up. Just a coincidence, but it happens.

Get that fuel pressure gauge and make sure you're getting fuel.
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SGKent Premium Member
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PostPosted: Sun Feb 15, 2015 4:57 pm    Post subject: Reply with quote

did you plug the AFM back in? That is the one most folks miss. The other one can be the ground wire at the double relay.
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sixer
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PostPosted: Sun Feb 15, 2015 5:35 pm    Post subject: Reply with quote

EZ Gruv- Thanks, I'll be checking as soon as I get the gauge.

SGKent- Without the AFM plugged in, the bus will start and idle, although it does idle high. With the AFM plugged in, the engine dies after it's warmed up. I am guessing the default rich condition with the AFM unplugged is covering up whatever my issue is. I will check the continuity of the ground wire for the double relay, but it is connected and I used the screw holding it as a ground point when testing some things earlier.
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busdaddy
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PostPosted: Sun Feb 15, 2015 8:10 pm    Post subject: Reply with quote

I'm guessing the AFM is plugged in as he's mentioned he sees flow through his incendiary time bomb filter, no AFM means no pump unless the starter is engaged.
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Wildthings
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PostPosted: Sun Feb 15, 2015 11:20 pm    Post subject: Reply with quote

Check to see that your TSII sensor is hooked up. This is how the ECU determines how hot your engine is. If the wire to the sensor is not connected the ECU will think the engine is stone cold and dump in way to much fuel as the engine warms.
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sixer
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PostPosted: Mon Feb 16, 2015 5:37 am    Post subject: Reply with quote

Busdaddy- Not sure what you mean, sorry. Incendiary time bomb filter? I have the standard square fuel injection filter plumbed in prior to the fuel pump under the bus. Are you saying the fuel pump should not run with the AFM unplugged, unless the starter is engaged? That is interesting. The engine would run as long as I asked it to with the AFM unplugged.

Wildthings- I've checked TSII sensor, it seems to fall within the specs listed in the AFC fuel injection guide. It registers around 5k ohms which is high according to the Bentley, (which seems to only give the value for room temperature) but falls right in line with the resistance vs. temperature chart listed in the AFC troubleshooting guide. It was ~30F out the morning I checked it. I checked the sensor both with the pigtail and through the ECU plug to eliminate any wiring issues. Unplugging the TSII sensor causes the engine to run very rough and die faster.
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busdaddy
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PostPosted: Mon Feb 16, 2015 7:27 am    Post subject: Reply with quote

sixer wrote:
Busdaddy- Not sure what you mean, sorry. Incendiary time bomb filter? I have the standard square fuel injection filter plumbed in prior to the fuel pump under the bus. Are you saying the fuel pump should not run with the AFM unplugged, unless the starter is engaged? That is interesting. The engine would run as long as I asked it to with the AFM unplugged. .

Whoops, I've confused you with another poster here who had one of those dismantleable glass filters in thier system, the square plastic one is just fine.
A bus will idle fine with the AFM unplugged but crap out when you give it throttle, there's enough gravity feed from the tank that the pump isn't needed for idle.
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sixer
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PostPosted: Mon Feb 16, 2015 2:46 pm    Post subject: Reply with quote

So, tonight's troubleshooting session started with:

1) Connected fuel pressure gauge, reading 38 psi with ignition on and AFM open, engine not running. Started engine, gauge bounces between 20-30psi wildly. As the engine warms up, it starts to stumble, and eventually stumbles more and more until it dies. Holds about 28psi of fuel pressure with engine off.

2) Applied power to cold start valve, fuel pressure dropped as it should.

3) Tested TSII again, read ~500ohms and steadily climbing on a warm engine.

4) Verified 20-30 ohms between contacts in AAR.

5) Verified double relay ground is connected.

Now what? Any suggestions? I am out of ideas. What would you check next?
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busdaddy
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PostPosted: Mon Feb 16, 2015 4:00 pm    Post subject: Reply with quote

What happens if you unplug the TS2 when it's warm?
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sixer
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PostPosted: Mon Feb 16, 2015 4:24 pm    Post subject: Reply with quote

Unplugging TS2 with the engine warm results in a very rough, surging idle, followed by the engine stopping. That is with the AFM unplugged, the only way it runs when warm. I tried to get it to run with the AFM plugged in and TS2 unplugged, but it refused.
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busdaddy
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PostPosted: Mon Feb 16, 2015 4:59 pm    Post subject: Reply with quote

It sure sounds like it's got a big vacuum leak, when you had the engine off did you remove the manifolds?, if you did are you sure a corner of the cylinder tin isn't pinched under one?, how about the brake booster hose?, didn't forget that one under the bus did you?
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sixer
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PostPosted: Mon Feb 16, 2015 5:09 pm    Post subject: Reply with quote

We did pull the (intake) manifolds. I will double check the tin isn't under one. Do you happen to have a picture of the likely culprit area handy so I know what I'm looking for? I did not replace the full brake booster line yet. I did double check the connection right behind the front tin. Actually, I plugged off the tee where it goes to the booster to eliminate that run as a possibility when I was hunting for vacuum leaks.

A large vacuum leak is exactly what we have been thinking as well, just can't find it.
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Wasted youth
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PostPosted: Mon Feb 16, 2015 7:54 pm    Post subject: Reply with quote

I have inadvertently cracked one of the phenolic blocks that go between the intake runner and the head on my 1700 a year or so ago. Developed a significant vacuum leak but didn't realize that's where it was coming from. Very easy to crack, I guess, but haven't had any troubles ever since. Worth a look. Once you take those runners off, you will need to replace the gasket material on those blocks before a carefully torqued re-installation.
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sixer
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PostPosted: Tue Feb 17, 2015 5:32 am    Post subject: Reply with quote

I'll definitely have a look at the intakes tonight. We did not replace the gasket material there (nor did we see any existing). Is there supposed to be a paper gasket on each side of the thick block, or a metal gasket, or a very thin smear of some gas-resistant RTV? Some reading and searching has told me that metal gaskets are recommended, but Copper Ultra RTV may work to get us on the road, and a few people mention paper.
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busdaddy
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PostPosted: Tue Feb 17, 2015 7:24 am    Post subject: Reply with quote

Metal gaskets and no block for carbs, paper each side of the phenolic block for FI.
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PostPosted: Tue Feb 17, 2015 8:31 am    Post subject: Reply with quote

busdaddy wrote:
Metal gaskets and no block for carbs, paper each side of the phenolic block for FI.


The 1700 I did that on had them.... but (!) it also has a Progressive carb set-up, with their intake runners. Don't know why they installed them on it, and at the time, I was pretty ignorant to the whole mess. Now I know... just a little bit more. Laughing

Why phenolic blocks on fuel injection? Could the conductive heat from the heads be that influential?
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busdaddy
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PostPosted: Tue Feb 17, 2015 8:53 am    Post subject: Reply with quote

Wasted youth wrote:
Why phenolic blocks on fuel injection? Could the conductive heat from the heads be that influential?

Keeps the injectors happy, especially after shutdown.
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sixer
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PostPosted: Tue Feb 17, 2015 6:29 pm    Post subject: Reply with quote

Just an update after a few hours in the garage this evening. Built a smoke generator and pumped some smoke into the vacuum system. By doing this, found out the gasket was missing under the oil breather box. That was the only source of smoke noticed so far. Installed a new cork gasket under there, and started the bus. That was not the problem, it once again ran great until it was warmed up, then started stumbling and died. Will smoke it again tomorrow to see if there are more vacuum leaks.

Any other ideas? Could it still be the intake manifold gaskets, even if there is no smoke coming out?
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busdaddy
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PostPosted: Tue Feb 17, 2015 6:37 pm    Post subject: Reply with quote

The breather box would definitely be a vacuum leak as well as valve covers and oil filler caps.
Assuming you replaced all the injector base seals and confirmed all the hoses were in good condition and fully connected when reassembling after the cleanup I wonder if you fixed a previous vacuum leak that the bypass and idle mixture had been adjusted to compensate for? Now that it's sealed up properly it may be too lean and low, is the bypass screw on the throttle body screwed in almost all the way?
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