Engine sputters and chokes at part throttle

[giantpune]

I just played with it a little more. I pulled the EGR valve off and filled the exhaust side with brake cleaner. None of it leaked over to the intake side. So maybe the vacuum part is busted, but the valve itself is stuck closed? I cleaned up the mating surfaces and installed it with a layer of RTV sealant.

Then I disconnected and capped almost all the vacuum things. The only thing that was still hooked up with the PCV and the brake booster. After running a while, the engine still fizzled out.

@Hemikiller The negative battery cable looks like its the same blue aftermarket one as the positive. The cable goes directly from the battery negative terminal to the engine block. As good as I can tell, everything is grounded pretty decently.

 

[RacerX]

The egr valve diagram is bad, not holding vacuum when you apply it. The valve closes off the port between the intake and exhaust. If the valve is stuck open, it can cause an intake vacuum leak.

 

[piper62j]

An egr valve should hold vacuum when applied. If not, then the diaphram has ruptured and it will creat a vacuum leak. Also, if the egr valve is stuck open, it creates a lean burn mixture at the base of the carburetor. Egr valves can be cleaned quite well with spray carburetor cleanter if they are carboned up.. My opinion is that your egr valve diaphram is leaking and the valve should be replaced.

 

[Hemikiller]

@Hemikiller The negative battery cable looks like its the same blue aftermarket one as the positive. The cable goes directly from the battery negative terminal to the engine block. As good as I can tell, everything is grounded pretty decently.

If you don't have any connection from the battery (-) cable to the body, I'll bet that's your issue. Factory cables had a ground strap the attached to the lower fastener of the voltage regulator.

 

[giantpune]

Welp...
It went from mostly working to not working. I drove it up to the gas station yesterday evening. Right when I got back home, i pulled into my driveway and got out to open the gate, and the thing died and would not start back up. I coasted it into my yard and tinkered with it a bit in the grass. When I first looked at it, the clear fuel filter was full of air. Fuel pressure gauge reading 6.5psi still, but there was a bigass air bubble in the filter.

I let the air out of the system and cranked the motor with the fuel line disconnected at the carb and its definitely pumping fuel. But when I connect that back to the carb, I can't get the thing to run. If I crank it, it'll fire a couple times, but wont run.

I pulled the coil and voltage regulator off my other 73 mustang. They are known working. They did not help. And I had an extra ground strap from the battery to the body right at the voltage regulator.

Edit -
I just took the valve covers off to see if I could see anything obviously wrong. Under both covers, I found a handful of chunks of something. It looks like parts of something that used to be round. The parts to not attract to a magnet. These were gathered around the oil return holes at either end of the head, and some of them were down in the hole occluding it.



Something else that looks odd to me are the heads themselves. They each have a couple spots where I can look down and see the lifters. Where the pushrods go through the heads, near the intake manifold, there's a couple big holes that look down all the way to the lifter valley. Is this normal on 351 cleveland heads?












Compression test says
1 - 140
2 - 140
3 - 140
4 - 145
5 - 140
6 - 100
7 - 80
8 - 120

 

[MAD IRISHMAN]

Most, if not all, is what's left of the valve guide seals. They harden over time and become brittle. Eventually they just fall apart.
Don't think this has any thing to do with the start/run problem but it's a problem of it's own.

 

[Steve McMahan]

I think those pieces are what remains of the valve seals. They were little hats that deflected oil from being sucked into the valve guides. Last engine I took apart had those pieces everywhere.

Low compression and two cylinder next to each other is not good. Maybe do a leak down test on those two. And, hopefully not, but a compression gas in the cooling system test. You can get strips to dip in the water to test for that.

 

[giantpune]

Low compression and two cylinder next to each other is not good. Maybe do a leak down test on those two. And, hopefully not, but a compression gas in the cooling system test. You can get strips to dip in the water to test for that.

Leakdown test showed both of them leaking through the intake. I have a feeling that means the heads are gonna have to come off.
If they do come off,I may use that as my excuse to slap on some aluminum ones.

 

[Steve McMahan]

Good choice. By the time you have the stock heads rebuilt, new hardened seats and exhaust valves, you’re in to them between 500 and 1K.

 

[Stanglover]

Well, I know really jack squat about motors, but with all the other issues you're having combined with the head valve stem seals and the fact that there is a lot of sludge around the valves, two or three bad cylinders, my thought would be rebuild time if the budget allows. Then of course the snow ball starts to roll and gets bigger and bigger. By the time you're done, you'll have a show room engine compartment.
I know because that was my exact experience.

 

[giantpune]

Well, I know really jack squat about motors, but with all the other issues you're having combined with the head valve stem seals and the fact that there is a lot of sludge around the valves, two or three bad cylinders, my thought would be rebuild time if the budget allows. Then of course the snow ball starts to roll and gets bigger and bigger. By the time you're done, you'll have a show room engine compartment.
I know because that was my exact experience.

Yeah. That snowball is what I'm hoping to avoid at this point. At the low end, it looks like I'm gonna be in it for a new set of heads, gaskets, coolant, and bolts, maybe a new set of pushrods and lifters and can do it all sitting in the car. And just hoping that the timing chain and bottom end are in good enough shape.

Anything much more than that, and I have to go yanking out the radiator, engine accessories, rip off the hood, and snatch the motor out. If I do all that, I'm not just gonna put back in some little 175 HP boat anchor rebuild.

 

[Stanglover]

Yeah. That snowball is what I'm hoping to avoid at this point. At the low end, it looks like I'm gonna be in it for a new set of heads, gaskets, coolant, and bolts, maybe a new set of pushrods and lifters and can do it all sitting in the car. And just hoping that the timing chain and bottom end are in good enough shape.

Anything much more than that, and I have to go yanking out the radiator, engine accessories, rip off the hood, and snatch the motor out. If I do all that, I'm not just gonna put back in some little 175 HP boat anchor rebuild.

Hmm, that snowball sounds like it might end up a snowman!!

 

[Hemikiller]

Valve seals for certain. Your running issue might be that bits of them got sucked up into the oil pump, locked it up and sheared the pin on the distributor gear. Pop the cap and see if the rotor is turning, or if you can spin it by hand.

 

[giantpune]

Valve seals for certain. Your running issue might be that bits of them got sucked up into the oil pump, locked it up and sheared the pin on the distributor gear. Pop the cap and see if the rotor is turning, or if you can spin it by hand.

Yeah, the distributor still appears to be spinning fine. I had the cap off and watching it spin around yesterday as I was doing the leakdown test.

 

[Steve McMahan]

Ok, so the really low buck solution is to do nothing.

Ok, that said, next spending level could be, pull the drivers side head, remove the valve springs on Cyl’s 6/7, inspect the valves, dress the seats the best you can (you can get a cheep seat dressing tool to do that), valves also, put it back together, new head gasket, retest cyl leak down. While I know many of the folks here will balk at that suggestion, if you’re not ready to do the rebuild you want, why do it half way?

Or, you could just replace the heads.

I guess what I’m saying, don’t do anything for a short term gain if it isn’t towards the longer term finish line; those are the mistakes I’m trying to avoid in my project.

 

[giantpune]

So next question I have is about pulling the motor. Local engine builder will rebuild this and deliver me back a long block for $2990. Its 9.5:1 compression and rated for 350 HP, using the cast iron heads. If I can go with aluminum heads and performer intake and get closer to 400HP and still be able to run the 87 octane, I may go that route.

I haven't pulled a motor out of a 73 mustang before. When I put one in, I had it attached to the transmission and installed the whole assembly as a unit. Is it feasible to pull the 351C out to have rebuild while leaving the C6 transmission in the car? The order of operations in my head, I always think of it is disconnecting the driveshaft and cooler lines, and then either removing the transmission from the bottom of the car or pulling it out with the engine.

Like @Steve McMahan said, its not advised to do things that are not working towards your final goal. My final goal for this car involves a TKX transmission. I dont mind leaving a C6 in there thats already there. But I'm not overly thrilled by the idea of pulling a C6 out and then putting it back. Id rather either leave it in, or put in the TKX. And this is exactly how we do that snowball thing we were talking about avoiding earlier. Its a very short trip from a new set of heads to a new transmission.

 

[Steve McMahan]

Since I have no idea how much mama will let you spend , so bear with my uninformed plan.
You could do step one, get a good short block, and decide on the head rebuild or new heads. Only you know if that will pass the “enough for now” test. Have fun with that for a year, while you plan step two, the trans swap. I mean, if the C6 works, I’d keep it for now.

And I’d pull them together because it’s more complicated to pull them separately, at least for me. BUT, if you do decide to just pull the motor, if you remove most of the front of the motor, you should be able to unbolt the converter from the flywheel and pull it forward without doing all of those things you mentioned.

I‘d do the engine and enjoy that until is not. My 2 cents.

 

[mrgmhale]

Hi!

I am getting to this post a little on the late side (traveling a bit). It sounds like the teardown is what will tell you what is needed. Sorry it had to be like that,. When it comes to rebuilding, or even partially rebuilding, an engine I have one main thought in mind - "invest once, do not spend twice." That works for most things in fact. In the case of repairing or rebuilding an engine I would suggest a few things. First, I replace the oem style excuse for oil seals (they are more like upside down umbrella style oil deflectors) with a real valve seal, like a Perfect Circle style seal. Also, I would have the valve guides bronze walled. I would also replace the valves with one piece valves, as opposed to the factory two piece valves that are friction welded together. Make certain the spring height and pressure is correct for your cam and lifters. I have decided that on all future builds I am going to use a hydraulic lifter cam and lifter kit. Make certain at least your exhaust valve seats are hardened steel. I avoid the own style nylon/plastic tipped camshaft gears, and prefer double roller timing chain with all steel gears - always use a very high quality set of parts there for sure. Unless you are racing the car on a track porting and polishing does little more than drain your money and give you bragging rights. Select aan engine builder that has experience with these older 351C engines.

I took note that several folks advised a vacuum test of an EGR valve ought not show any leaks. In general that is correct, especially for the earlier EGR valves. But, in the 80s Ford began to use EGR valves that were intended to have some (very slow) bleed-off when vacuum was applied, which was intentional by design. That bit me as a tech once, and only once, on a warranty job I had back in the early 80s.

I have found a lot of folks who began to mess around with those emission control systems and the vacuum line routing could find themselves in trouble in a hurry. And, I get why. Until 1972 the factory manuals did a poor job of providing useful info on vacuum routing, much less emission control systems. In 1973 the Forel shop manual for Mustang (and Cougar) finally provided some really good into in Volume 6 of their shop manual. But, as good as it is they left out the 351 4v engine vacuum line calibrations.

As for pre-1973 Mustang Barn took the time to collect 67-72 vacuum routing and offers that info on a no fee basis. With their knowledge and permission I consolidated all of their schematics into a single PDF file, grouped by year and sorted by engine. Attached are the 67-72 vacuum schematics, a snippet for Volume 6 of the 1973 Forel Shop Manual (I added the two missing 351 4V calibrations to my copy of Volume 6), and the two 351 4v calibrations that were missing from the 1973 shop manual for anyone who ma want or need that info. Also, following is the link for the Forel Publications page where you can navigate to the year Mustang you need manuals for, then for a very reasonable price you can purchase and download lots of great manuals:

https://www.forelpublishing.com/clickbank/index.html

Once you get your engine back in running I hope you post a followup.

 

[Stanglover]

That damn snowball!!!
On my car it's a bit easier as it's a 4 speed manual, but pulling and replacing as a unit worked well for me. Regardless, I would say to pull the front end off completely, unless you have a minimum of a 2 ton hoist with a long enough beam. On my 71, I had to do that and although a bit more work, I didn't have to worry about damaging the urethane bumper or grill.
Once you get that motor back in, then you'll probably need to time it for optimum performance. That's a whole new subject for discussion later.

 

[71coop]

Good choice. By the time you have the stock heads rebuilt, new hardened seats and exhaust valves, you’re in to them between 500 and 1K.

Normally I would agree, but not with a 351C. Keep in mind I really like the trick flows (running a pair now), but if you sink a grand into your factory heads, you still can't buy one aluminum head for the same price.

On almost $3K for a complete rebuilt long block - that's really not bad if the builder does it right. I'd take that all day long. I have a CJ short block with the small chamber/large port heads in the machine shop now, and I expect to pay more than that. Granted, I'm doing screw-in studs and new forged pistons, but it'll be worth it.

$3K for machine work, clean and labor to rebuild is a good deal.