cylinders 1 and 7 are cold

[Graeme Stebbing]

Hi John, Have you checked the fuel pressure, I have just resolved an issue like you have with a BMW v12, and I even had the fuel rails off spraying the injectors into air all looked good, when exposed to the atmosphere, but not getting enough fuel when the injectors were installed in the manifold. It turned out to be a weak fuel pump some injectors did not get enough fuel depending on their position on the fuel rails. Have you also checked the fuel pressure regulator on the rails.

 

[John Milmont]

Yeah, I have a fuel pressure gauge on the dash which is telling me my pressure is perfect. If the regulator was was a problem, i would see it on the pressure gauge. Also, if pressure was an issue, it wouldn't be isolated to these cylinders.

I have a feeling my problem lies within this intake.

 

[Jac Mac]

John, the 300° you mention, are we talking Celsius or Farenheit & are the two offending cyls EGT's 300° colder than the others by that amount or just registering a temp of 300°?

I 2nd Randys suggestion of a single probe & meter to check all EGT's to eliminate errors, when checking Jet Boats I simply clipped the probe to a piece of #8 wire about 3ft long and placed it each header tube while flat out on the lake, good fun with that harmonic balancer spinning at ~6000RPM about 1 foot away from your face!

 

[John Milmont]

Fahrenheit.

This is the actual temp of the cylinders (EGT) but its probably not all that accurate since I'm measuring it with an IR thermometer. But, it is clear that those cylinders are missing as a simple exam of the spark plugs tell the story.

I just took the intake off again and I'm thinking there's some sealing issue. I did notice some oil on gasket at the bottom of the port, but I'm not totally sure. I had the intake off before and didn't notice this. I think if there is a leak is must be minor. Then, stupid me, as i was scraping the old gasket off, i slipped and broke the razor blade i was using. It snapped off and shot down one of the intake ports and is now in the cylinder!!

I ordered some tiny magnets to try to fish it out, but I think i will have to take the head off now... DAMN IT!

 

[Bill Musarra]

John,
Check with your friendly auto parts store(Advance, Pep boys etc.) and see if they have a scope for rent. Maybe they do. If not check with a auto garage that does high performance engines, drag cars etc. Its better than having to pull the head. Then you can put the magnet on the end of the scope. Worth a try. Next time you take on that chore stuff some rags down the ports.

Bill

 

[John Milmont]

Yeah, i know i shouldn't have done anything without the ports plugged up. Its amazing, it was just a small little piece of gasket that was all lonely on that part of the head...

If anyone is local with a borescope, a helping hand would be much appreciated.

 

[Randy V]

I would just not rotate the engine, pull out the spark plug and use a small magnet on the end of a flexible wand down that hole.. You will be able to fish it out easily that way. If you are worried about any other potential debris or dirt, you can get a short length of tubing that will fit into the plug hole and duct tape the other end to a shop vac and then move it around to vacuum the top of the piston.

Anything else will blow out the exhaust port the instant it is started..

 

[John Milmont]

got it!

 

[Randy V]

Congratz on the successful retrieval!

 

[Jeff Young]

It's got to be fuel or timing related (if the manifold is ok), and I suspect an issue with the ECU. Do you have any ability to log what the ECU is doing?

 

[John Milmont]

Yes, I have logged what the ECU is doing and everything looks fine. I have actually tested all of the injectors and they are good.

I'm in the process now of trying a different intake manifold.

 

[John Milmont]

Well, I am very depressed. I just got everything back together and nothing has changed. The car still runs like crap.

I decided not to use the different manifold I have because its not complete, doesn't clear the hood of the car, and I would have to change how my fuel lines would connect to its - so I stuck with the LT-1 manifold.

But this time, I made certain that there couldn't be any leaks into the valley. It looks like there could have been some issue with the bolt holes on the intake, so i opened those up a little and also used a lot of that blue Permatex Gasket Dressing around the ports to make sure there was no leaks. The intake fits well and I'm sure there cant be any leaks.

But yet, the car still runs like crap and cylinders 1 and 7 are still cold.

I just don't know what to do any more.

I'm trying to think of anything else it could be, but nothing seems to make any sense.

If it was an ECU problem, it doesn't make any sense that only cylinders 1 and 7 would have problems.

Could it be ignition noise interfering with something? I don't know.

 

[craig]

Do plugs 1&7 come out looking dry or wet after running it.
Also have you checked injector pulse while running.

 

[Ron Earp]

Okay, you say you have spark and it is timed correctly so we have to believe you on that end. That part is out of the diagnosis.

But you have no combustion, so, you must not have a combustible mixture. I'd check:

0. Is the injector firing and spraying fuel? A few ways to check - pull the spark plugs on 1/7 and run the engine, you should quickly have fuel vapor flying about. Or, pull the injector plug and check with sillyscope to verify pulses, at the same time pull the injector and swap with #2,3,4,5,6,8 that you know is firing finet.

1. Cam lift. You can do this with a hydraulic cam, no problem. Pull valve covers, break out the dial indicator, and check it up.

2. Should do this first, but have you checked compression on #1/7? $40 gauge, 10 mins of work. If #1/7 got no compression you have you part of your answer.

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My guess is you have a wiring problem and injectors #1/#7 are not spraying fuel. No fuel, no bang. No bang, poorly running engine.

 

[John Milmont]

Okay, you say you have spark and it is timed correctly so we have to believe you on that end. That part is out of the diagnosis.

But you have no combustion, so, you must not have a combustible mixture. I'd check:

0. Is the injector firing and spraying fuel? A few ways to check - pull the spark plugs on 1/7 and run the engine, you should quickly have fuel vapor flying about. Or, pull the injector plug and check with sillyscope to verify pulses, at the same time pull the injector and swap with #2,3,4,5,6,8 that you know is firing finet.

1. Cam lift. You can do this with a hydraulic cam, no problem. Pull valve covers, break out the dial indicator, and check it up.

2. Should do this first, but have you checked compression on #1/7? $40 gauge, 10 mins of work. If #1/7 got no compression you have you part of your answer.

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My guess is you have a wiring problem and injectors #1/#7 are not spraying fuel. No fuel, no bang. No bang, poorly running engine.

Hey Ron,

I don't think I have ever put an indicator on the cam to measure lift, but its a brand new comp cams hydraulic roller. I have moved the lifters around from the 'bad' cylinders to the good ones and have not noticed any change. If the lobes are not correct on the bad cylinders, it would have to be a very small error. Visually, those cylinders look like they open just as much as any of the others. How much lift has to be 'missing' before things don't run anymore?

The engine is batch fired and it alternates from bank to bank. That means all of the injectors on one side of the engine fire at once. This allows me to take off the connector from one injector and move it to another. I have done this and also moved the injectors around from cylinder to cylinder. I have also removed the entire fuel rail from the engine and had all of the injectors fire into graduated cylinders so I could measure how much fuel each one puts out. All of them are perfect.

I have measured the compression and done leakdown tests on all cylinders. All of them are within spec. I recall cylinder #7 being 195psi.

I would really like to get this ancient mythical tool called the sillyscope, but no one seems to have them anymore and I cant find a shop anywhere that has seen one in 25 years. They also seem to be very expensive. If you know someone whos got one, i would like to know.

 

[Ian Anderson]

I believe an LED across the injector connector will visibly blink in time with injector pulse.

Cheaper than the silly scope!

Ian

 

[John Milmont]

Well, i know that its firing because i can move a known firing injector with its connector from a good cylinder to #7.

I would like an Oscilloscope so I could check for noise...

 

[Randy V]

Hi John,

Sorry to hear you are still battleing this dragon...

I can't recall if we have already covered this but...

Have you checked the headers to make sure that the tubes are open all the way down to the collectors?

Point is, if the exhaust is blocked, you will not get flow and those cylinders that are blocked will not fire more than a couple of times before they are no longer capable of being refreshed with oxygen.

Would be a pretty odd duck to fine just one bad header tube let alone two...

You could just loosen up the headers to introduce a massive leak to run for a few moments to see if you at least have all 8 firing..

 

[Robert May Eng.]

Well, i know that its firing because i can move a known firing injector with its connector from a good cylinder to #7.

I would like an Oscilloscope so I could check for noise...

Its just a thought but if you still have the cam card it might be worth checking you haven`t got one of those odd ball chevy hipo cams with the other firing order 1-8-7-3-6-5-4-2. Other than that I would be checking the dizzy phasing.

Bob

 

[Chris Kouba]

Yeah, to me this screams firing order. If everything else checks out, something basic has to be off.

I once "had a friend..." who tried to get his motor to start and set the firing order extremely accurately. Four hours later, "he" finally figured out the distributor's counter-clockwise rotation didn't work too well with the clockwise wiring install sequence. DOH!!! Swapped them around and PRESTO!

It may be worth pulling the valve covers to verify firing order as Bob indicated. Other than that, I'm stumped too.

Best of luck,
Chris