Slight Knock At Start-Up

[ScottPuddintane]

I'm baffled....

I just put in a salvage yard '04 SOHC into my '96 GT. The engine only had 117 miles on it (about 400 miles now). I have REALLY babied it & I have great oil pressure. I'm still using all the high-mileage '96 bolt-ons, throttle body & associated parts, etc.

When I very first start the I hear a very slight knock/misfire ??? for about 1/2 second. It sounds like a mild version of what I heard when I first started the engine with 3 plug wires mixed up on the coil packs.

I cleaned the MAF wires very well, but no change. My Air/Fuel gage has been cycling a lot more towards the lean side (did it before engine swap too) if that means anything.... and I just put in fresh plugs with quite a bit of boot non-stick stuff.

Any ideas???

 

[sgarlic]

Try swapping oil filters.. if it has a bad drainback valve it can cause that knocking at startup you describe (if it only happens at cold startup.)

 

[Kilgore Trout]

Try swapping oil filters.. if it has a bad drainback valve it can cause that knocking at startup you describe (if it only happens at cold startup.)

Swapping oil filters is a great suggestion. Use Ford oil filters, they have drainback valves for sure.

Also, the 4V has a known common problem called "cold start rattle". Sounds like you have a 4V that has this problem...

Edit: Just noticed that you said SOHC... I am not sure if the SOHC also has the cold start rattle, I do not think it does. I am researching it...

 

[ScottPuddintane]

Wow.... an oil filter???? I've never heard of that, but it's cheap enough to just try so I'll give it a shot.

FYI it's one of those Fram PH2's with the "grip" on the end & I put it in during the engine swap.

Thanks for the help.... and just curious... why does it cause this problem on the DOHC's?

Any other ideas?

 

[Dave Holman]

I have a 99 GT (50K miles) that made the noise you described at startup when cold. I now use Lucas synthetic oil stabilizer and that noise can no longer be heard. It is made to prevent dry starts and in my opinion its well worth 12 bucks to not hear it rattle at startup.

 

[bdcardinal]

never use the Frams on the 4.6 motors. the motorcraft filters are cheaper and filter better.

 

[ScottPuddintane]

Well, I changed the oil filter & it still rattles for 1/2 second on start up.

After listening more carefully to the engine I am 99% sure that it is actual "spark knock" and not oil related.

I am using the ignition crank "star wheel" from the 2004 engine, but the magnetic pickup is from the '96 engine. I noticed that the '96 & '04 "star wheels" look slightly different. Could that be the problem?

What else would cause "spark knock" ONLY during starting?

 

[forpit2000gt]

why didn't you use the sensor from the 04? I haven't seen an 04 but don't think that would matter.

 

[ScottPuddintane]

The '04 sensor was destroyed in the accident that got the me the engine.

Does anyone know anything about the crank sensor & "star gear"? Are the sensors/gears interchangable.

I'm running out of ideas here......

Has anyone run into this problem where the car "knocks" only for 1/2 second while cranking the engine? What could this be?

I've got about 600 miles on the engine & a full tank of nitrous oxide & I'd like to go to the track this weekend......

 

[forpit2000gt]

first off, the A/F guage should not be trusted for problems, it is little more than pretty lights. Are all the injector connections snug. If you turn the key on and off a couple of cycles before cranking will it do the same? Hot and cold starts? Did you change the fuel filter?

 

[ScottPuddintane]

I checked the injector plugs already, but I will double check them. I changed the fuel filter yesterday.

The engine "seems" to do it less when warmed up, but it still happens. It is definitely more prone to this "ping" when cold.

What are you thinking about the on/off with the key? I'll give it a try right now & see what happens.

Anyone with any ideas on the crank ignition "star"?

 

[forpit2000gt]

by cycling the fuel pump on and off , you make sure to have plenty of fuel and fuel pressure at starting. sometimes a dirty fuel filter can cause this as well. I haven't heard spark knock at startup, if that is what you are even dealing with. If you have a chip or hand tuner , remove and test. I can't say for sure because I haven't seen an 04 but I don't think the crank sensor is a problem. sre you using the stock MAF or the 04 MAF?

 

[trinity_gt]

My 02 GT also has a bit of a cold start rattle, just a 1/2-second after start. Of course, it also suffers from the death rattle for another minute or so after I start driving it cold, just like Ford talks about in SSM #15934.

But my case is definitely a mechanical thing, not spark or fuel. It's just a bit of a rattler cold. It's been doing it for ages and is still strong & not burning oil so I've ceased agonizing over it...

 

[ScottPuddintane]

I tried to cycle the fuel pump (key on, but not start) 3-4 times and I still have the "ping" at startup. I am using the stock ('96) MAF which I just removed & cleaned the wires on (the first thing I tried). I am still running the stock chip.

I'm baffled & scared as hell about running it on the bottle with even a tiny question about the engine..... any more ideas???

I will try to change out the plug wires today & double check the injector wiring. I might even spray them with electrical cleaner.

 

[2013 Geee T]

I just posted a question about this right before seeing this one. I dont mind the rattle as long as its not hurting anything.

 

[ScottPuddintane]

Well, as far as I know, ping IS hurting something..... my rings, my pistons, my rod bearings. I don't want to grenade the motor on 150hp worth of nitrous 'cause I overlooked something. I'm just scared to run the bottle.... or even just let this go without fixing it for that matter.

If I knew for sure what it was, it might be a different story.... but right now it's a bad sound in an engine with only 600 miles on it....not good.