Engine Troubles

gamh44

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Jan 1, 2019
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I removed my 5.0 HO (circa 1989) recently to replace a couple of gaskets and fix some exhaust leaks. While it was out, I decided to check the condition of the bores so off came the heads and out came the pistons. It could probably do with a bore to 0.030” over but that will have to wait for now.

In the interests of full disclosure, the engine is in a Cobra and has Trickflow heads and cam and a MassFlo (now Pro-M) EFI setup.

Anyway, after buttoning it all back up, it is now a complete mess. It is hard to start but more importantly it runs horribly. Feels like it is running on three cylinders - coughing and spluttering and such.

Sounds very much like me to a timing issue so I checked everything in that regard.

Plugs are connected in the right order and TDC has been confirmed - with a piston stop and also with a dial indicator. I checked to be sure the dizzy isn’t 180* out. I even tried spinning it in frustration, which was of no help.

What in the world have I done to this thing?

I am sure it will be something simple that I have missed.

Any thoughts muchly appreciated.
 
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dgollem

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May 5, 2004
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Check for vacuum leaks. You had the intake manifold off, double check all the hoses etc then check the intake gasket is not leaking don't forget there is a large vacumm port under the back side of the intake that could have been overlooked or popped off.
 

gamh44

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Thanks for the reply. I hooked up the compressor at about 15psi this afternoon and found no leaks. I used liberal amounts of soapy water to check. Good news is the engine is nice and clean now. All connections are good and tight.
 

Mstng93SSP

You have a nice rear end there Dave.
15 Year Member
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Sounds like a timing issue. Because I don't know your skill or knowledge level I will say this but you may already know it. Firing order is 13726548. Cylinders are 1234 passengers side front to back and 5678 drivers side front to back. Pull #1 plug, but thumb over the spark plug hole and turn over engine by hand. When the compression "pops" your thumb out you are close to top dead center on the compression stroke and timing mark should be close to zero on harmonic balancer. Rotate the engine back slightly by hand and line up the timing mark on 10 degrees before top dead center. Now rotate the distributor so the rotor points at the #1 plug on the distributor cap. Verify your plug wires are on the cap in the correct firing order. Start engine and set timing with a timing light and the spout removed. After timing is set put spout back in. After this is done it will either run right or timing can be eliminated as a cause of your issue.

Chris
 

gamh44

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Jan 1, 2019
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Chris

Yep, sounds very much like timing to me as well. Although my experience is indeed limited so any advice is appreciated - thanks.

I have checked TDC with a piston stop and a dial indicator. Both match the harmonic balancer markings. I have confirmed the #1 firing position with the thumb in the plug hole as well as following valve events with the cover off. In frustration, I even spun the distributor 180* just to see what happens - no dice that way either.

Plug wires are set up as per the 351/HO firing order. Initial timing is set at 10*. I also confirmed this with a timing light on the starter with the injectors disconnected.

So sounds a lot like timing but may well be something else.

Cheers
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Ok, I'm going for a shot in the dark here.
Since this is an engine swap to a cobra car and everything was fine and pulled it to fix oil leaks, is it possible when you reinstalled the engine you flipped the injector harness so now the left bank injectors are on the right, right bank on the left?
 

gamh44

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Codes are 15 and 95. Had them both for years.

I have checked the injector harness. I actually have the numbers printed on the plugs. Also checked a few of the plugs were connected to the right pins at the ECU in case some plug got misconnected somewhere. Did the same for the TFI.

Cheers
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Ok, lets go about this methodically, go to the 'surging idle check list' here, I post a link-
Do the list step by step, don't skip around just because you have replace something or you think it's fine. The next step depends on results from the one before. I had to read it a couple times to get it, so take notes or you will hurt your brain.
 

gamh44

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General

Thanks for the reference. I will follow along and see how I go. Plenty to do there!

I'll also have a look at the Cranks OK, but No Start Checklist for Fuel Injected Mustangs list, given it is quite difficult to get going.
 
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gamh44

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Thanks again for all the replies.

Before I started on the checklist, though I'd just replace the coil and plugs so I know where I am starting from.

So did that, fired it up and it started and ran just fine. Not sure which was the cure (if not both) but I am surprised that either would have caused such rough and mistimed running. Also not sure why disconnecting these and reinstalling them caused them to fail, since it was running fine before I took the engine apart. Probably just another coincidence.

So thanks again!!
 

revcor

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Jan 11, 2015
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If you’re curious (I know I would be) you could always put the old plugs back in and leave the new coil. Try to fire it up, if it runs fine it was the coil, if it goes back to running like :poo:, it’s the plug(s). And if you want to really specific, start replacing one plug at a time with the new ones, firing it up after each one and see which plug(s) makes a difference. Or vice versa, i.e. first step being leaving the new plugs in and reinstalling the old coil.
 
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