cam? need help
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cam? need help
I just had my engin in my 89 f250 rebuild (5.8 H.O efi) engine surges
at idle, 800rpm down to 300rpm , then will stall unless you give it throttle, I was told They may have put the wrong cam in? The shop said that was the cam that came with the kit that I brought them, I need to know how I can find out what cam I need to put in, to make it factory complient with the computer, Every autoparts store seems to have multible models and sizes......need help!
also would this be a proper diagnoses to my problem?
at idle, 800rpm down to 300rpm , then will stall unless you give it throttle, I was told They may have put the wrong cam in? The shop said that was the cam that came with the kit that I brought them, I need to know how I can find out what cam I need to put in, to make it factory complient with the computer, Every autoparts store seems to have multible models and sizes......need help!
also would this be a proper diagnoses to my problem?
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Have you driven it yet?
Or did you notice the surging and shut it off right away?
2 Possibilities that I'm aware of.
1: The cam won't work with the computer you have.
2: The computer needs to adjust it's fuel tables.
Surging on initial startup with a new cam is not unusual for speed density vehicles. If possible try driving it. If it's just a matter of the computer adjusting itself, then a short 20 minute drive should cure the surging. Normal driving, preferably including time on the highway.
First, check that everything is properly connected. All vacuum lines, all sensors, all electrical grounds. Then drive it.
As for what cam to use. The primary consideration is the lobe seperation. Needs to be greater than 112 degrees. Preferably 114 or more. I'd call the cam manufacturer to see what they say.
Or did you notice the surging and shut it off right away?
2 Possibilities that I'm aware of.
1: The cam won't work with the computer you have.
2: The computer needs to adjust it's fuel tables.
Surging on initial startup with a new cam is not unusual for speed density vehicles. If possible try driving it. If it's just a matter of the computer adjusting itself, then a short 20 minute drive should cure the surging. Normal driving, preferably including time on the highway.
First, check that everything is properly connected. All vacuum lines, all sensors, all electrical grounds. Then drive it.
As for what cam to use. The primary consideration is the lobe seperation. Needs to be greater than 112 degrees. Preferably 114 or more. I'd call the cam manufacturer to see what they say.
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I've beendealing with this problem for about a year, I've replaced every sensor, distributor, every thing, but it seems to start when engin reaches operating temp! I saw a posting in here where someone else was having the same exact problem after a rebuild, and he found it to be the cam. also my truck ran great before the rebuild, but had a knock, and low oil pressure, also It seems that I don't have the power I had before, I was able to spin tires on dry pavement prior to rebuild!
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I agree. Most of the time the computer will adjust itself, but a lot of the time you just need to adjust the throttle position sensor. The voltage sometimes gets knocked off a bit when you take the engine apart. I have even gone as far as drilling a small hole (no larger than the thickness of a paperclip) in the throttle body plate, and making it larger one step at a time until the idle smooths out. That is kind of a hack way to do it, but it works. I would also check the fuel pressure, and the color of the plugs. Leaning out the car tends to smooth out the idle.
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From: Calhoun GA
If you're not running mass air, and this cam is not "speed density friendly", then it will surge no matter what you adjust and/or tune. Cams with less than 114* lobe separation do not produce enough vacuum at idle and this will cause it to surge. Getting those cam specs is kind of important right now.
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what is speed density? little clueless about some of these things, and I don't really know what cam kit I got it was part of a federal mogul master rebuild kit, and was very cheap. the machine shop that did my engine work got the kit I just assumed it was all correct, also too besidesthe knock the engine ran great before the rebuild, I called Melling to ask for a suggested cam, they told me the only cam that would replace the factory cam was a syb-35, they said that was the only cam that will work with the stock ECM!
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Well don't call mellings.
You can call crane or comp cams, they have a camshaft waiting on you that is speed density friendly and provide you with more power.
Unlike mass air you need a camshaft that produces roughly 17 hg at idle or better, this can be done with a camshaft that has a lobe seperation of 114-115, any cam company has what you want or to get the cheapest cam possible just to see if the one you have is the problem, go into any parts store and ask for a replacement camshaft for your 89 351w and use new lifters everytime you change the cam.
You problem could be attributed to a vacuum leak, crossed vacuum lines or faulty TPS, etc.
You can call crane or comp cams, they have a camshaft waiting on you that is speed density friendly and provide you with more power.
Unlike mass air you need a camshaft that produces roughly 17 hg at idle or better, this can be done with a camshaft that has a lobe seperation of 114-115, any cam company has what you want or to get the cheapest cam possible just to see if the one you have is the problem, go into any parts store and ask for a replacement camshaft for your 89 351w and use new lifters everytime you change the cam.
You problem could be attributed to a vacuum leak, crossed vacuum lines or faulty TPS, etc.
Last edited by Motorhead351; Sep 22, 2004 at 04:55 AM.
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Speed density is a type of fuel and timing management controlled mainly by your map (manifold absolute pressure) sensor, and you coolant temperature sensor and your throttle position sensor. It is programmed with very specific tolerances based on your specific vehicle. It does not respond well to changes in things such as cams, heads, intakes, and etc. The reason that it does not react well with those changes is because those upgrades change the amount of fuel, air and timing avance needed at a specific rpm. Since speed density has a pre determined amount of timing advance and a specifically prgrammed fuel curve, you will get rich and lean spots through the entire rpm range (I can go on and on with this), you will get very poor drivability, and a surging idle. My guess is that you have the correct cam, you are just over looking something like a vacuum leak, or a throttle position sensor that has not been adjusted correctly, or too much fuel pressure. Keep working on it, you will find the missing key.
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From: Still under the hood in O
As said earlier......found out what the specs are for the current cam (VERY important).
From the sound of it (loss of low end power), the cam is too large and most likely on a 110 LSA. (this cam wouldn't have been for a Mustang would it?)
From the sound of it (loss of low end power), the cam is too large and most likely on a 110 LSA. (this cam wouldn't have been for a Mustang would it?)
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From: Calhoun GA
Originally Posted by 90f150moneypit
As said earlier......found out what the specs are for the current cam (VERY important).
From the sound of it (loss of low end power), the cam is too large and most likely on a 110 LSA. (this cam wouldn't have been for a Mustang would it?)
From the sound of it (loss of low end power), the cam is too large and most likely on a 110 LSA. (this cam wouldn't have been for a Mustang would it?)
The easiest thing to do is to check for a vacuum leak. It is still important to find out what rebuild kit you got and get the cam specs. Put a vacuum gauge on it as well....oh, check your base timing too.
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I've have replaced just about every senor on this truck, (tps, egr, whole disdributor sensor temp sensors, feul pressure reg, ) fuel pressure is running about 35psi, on thing is though when the engine was first installed I had removed the new thermostat it was now opening far enough and would run real hot, one thing I have noticed that my truck only seems to have the surge problem at idle after the engine has been running for about 15 mins, up till then my rpm at idle is around 1000, it appears that when the engine reachs normal operating temp, the rpm will drop to around 650, that is when the surging starts, it will go from 650 to 300 to 650 to300 then will stall , Ive played around so much with the tps and no change.
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From: Calhoun GA
Well...in that case, if it was the cam, I think it would do it from start up to shut down.
It sounds like the problem is when it goes into closed loop. An EEC-4 engine monitor might be able to tell you what is going on. Any Ford dealer and most repair shops will have one of these. These trucks are also known to have problems with the ignition module when they get warm. Just something else to think about
It sounds like the problem is when it goes into closed loop. An EEC-4 engine monitor might be able to tell you what is going on. Any Ford dealer and most repair shops will have one of these. These trucks are also known to have problems with the ignition module when they get warm. Just something else to think about
