6 cyl. question please.

[Gig Pig]

So I'm going to be replacing my current 6cyl.in my 87 Comanche & my question to you is, Will a newer (say 95) 4.0 HO plug in the same as my current 4.0 or is the head different? If I remember correctlisn't the intake different. Thanks for any help. :thumbsup:

[Pete M]

I thought you said the compression numbers were good? :hmm:

[Eagle]

So I'm going to be replacing my current 6cyl.in my 87 Comanche & my question to you is, Will a newer (say 95) 4.0 HO plug in the same as my current 4.0 or is the head different? If I remember correctlisn't the intake different. Thanks for any help.

You are correct, the HO head is different and the intake & exhaust ports are higher and shaped differently.

[Gig Pig]

I thought you said the compression numbers were good? :hmm:

They are. I'm just afraid I'll spend countless hours trying to get it running right. Its just easier for me to replace it with something I know runs right. This sucks, because I'm a green person and hate to make waste. :ack:

[Eagle]

I thought you said the compression numbers were good? :hmm:

They are. I'm just afraid I'll spend countless hours trying to get it running right. Its just easier for me to replace it with something I know runs right. This sucks, because I'm a green person and hate to make waste. :ack:

But if you don't know why it's not running right, how do you know replacing the engine will cure it? If the problem is in the ignition or the fuel delivery system, which presumeably would be retained, you could be doing a lot of work to no benefit.

 

Remember: "If it ain't broke, don't fix it." Over the years, I have expended considerable time and money "repairing" things that didn't solve the problem. I even did what you are contemplating. I built a complete new engine for my 1968 Javelin, put it in ... and found that the new engine didn't run any better than the old one. I thought the old one had jumped timing. Turns out all it needed was a carburetor rebuild. That turned out to be the most expensive carburetor rebuild in the history of the western world.

 

My advice, as one who has made just about every mistake possible, is to be sure you know what's wrong before you spend a lot of time and money fixing it.

[Gig Pig]

Yes. I agree. Ive decided to stick with this engine. I'm going to pull the head since I already have the manifolds off & 1 broken exhaust bolt. That way I can take a peak at the pistons & walls. Probably have the head checked out as well. Havnt got much done because its so damn cold here. I'm itchin to lift it, but promised myself I wouldn't till i get it running right.

[Pete M]

Compression numbers and oil pressure are about all I worry about in the block itself. If those are good, I keep it and work with the peripherals. If all the rockers are popping up and down without undue noise, then I consider the head to be good. These old engines are practically invincible. It's the 20 year old sensors, timing chain, etc that I focus on. You'd be amazed how many headaches a simple vacuum leak or bad ground can cause.

 

Let's start with the basics. What seems to be the trouble with the truck?

[freakjeep93]

i think i recall it running rough

[Gig Pig]

 

Let's start with the basics. What seems to be the trouble with the truck?

It ran like it was only running 0n 4 cyl.'s. No knocks, good compression. Exhaust manifold was toast, so I removed old one & have a new one. 1 exhaust bolt broken & in the process of repairing it. So I guess next thing is I'll pull the valve cover and check there. Put exhaust and intake back together.

[freakjeep93]

okay I'm gunna sound like an idiot but did you check spark plugs and wires and that all 6 plugs hads fire.

if that all checks out check thpse 2 injectors. if their fine try distributor

[Gig Pig]

okay I'm gunna sound like an idiot but did you check spark plugs and wires and that all 6 plugs hads fire.

if that all checks out check thpse 2 injectors. if their fine try distributor

Did not check them, but all was new. I better put the manifolds back on & check some more basics.

[freakjeep93]

ive had brand new spark plugs that fired but the fired at the bottom of the insulator :eek: not where they were supposed to it was nuts it looked like the insulator was sparkin. but yea check all the basic stuff. ive always been taught that if somethings wrong it normally something simple

[Gig Pig]

After putting a new head & exhaust manifold on the truck, it ran exactly the same as before all the work. Only reason I put a new head on it is because I got a great deal on it. Anyways. After some simple test's I found that cyl. # 6 has no spark. Popped in a good used distributor I had on the bench & the same thing. No spark on 6. Any tips for diagnosing when be greatly appreciated. :bowdown:

[jimoshel]

Unfortunatly just because somethings new doesn't mean it's good. I don't know how many times I've taken a shiney new item out of the box, put it on and it didn't work. Then the biggest mistake to make is to start swapping parts. Waste of time and money.I can't think of a think in the electrical system* that can't be checked and verified as to good or bad with a good VOM. You'l need a spec sheet or manual to get the proper readings but if you're going to be doing any work on your Jeep at all, you should have one anyway.

*Computers, ECU'S excepted.

[Eagle]

After putting a new head & exhaust manifold on the truck, it ran exactly the same as before all the work. Only reason I put a new head on it is because I got a great deal on it. Anyways. After some simple test's I found that cyl. # 6 has no spark. Popped in a good used distributor I had on the bench & the same thing. No spark on 6. Any tips for diagnosing when be greatly appreciated. :bowdown:

More changing things that didn't need to be changed.

 

What does a "distributor" do? It "distributes" the spark among the cylinders. If the distributor is sending spark to 5 out of 6, why would you think it isn't sending spark to #6 out of 6?

 

Easy to check. Remove the spark plug wire from the #6 turret of the distributor, put in a new, known-good wire, crank the engine and see if the new wire sparks to the block. If it sparks to the block, then see if it'll make the plug spark. You may have a bad wire, or a bad plug. There really isn't anything else it can possibly be.

[Gig Pig]

Sorry. I diagnosed it wrong. I should of said that it isn't firing on that cylinder. I just figured it was spark. But no. I just ran outside & pulled the pug & it is sparking. Must be fuel. I'm 100% sure its not firing on that cylinder. I'm going to check the injector tomorrow. Any tips on that?

[jimoshel]

Start and run the engine 10-15 seconds. shut it off. pull the no 6 plug. See if the tip is wet. If it's wet your getting fuel but it's not firing. If it's dry your not getting fuel. If you have a VOM or test light pull the injector plug. Check for voltage.It will be a pulsating voltage depending on RPM. Or swap injectors. Another way. Start the engine. Pull the plug on the injector. Be careful for the C clip. They love to fly off, never to be seen again. Listen to the engine. if it slows down that is a good injector. If nothing changes it is a bad injector, or it's not getting a signal.

[Gig Pig]

I will. Have to wait till tomorrow though. If its dry, I'll swap injectors out. Thanks for your help. I'm just excited its getting closer to running right. Then I can order my lift.

[Squeegy410]

I Have the exact same problem with a '75 ford maverick i have. It has a 250 straight six in it and it fouled out cylinder six. I replaced wires and plugs as a prelimenary, that didn't help so we checked the compression on it and the cylinders were all fine exept six. it gets fire, it just doesn't do anything. The 250 is a cursed engine with a intake manifold built into the engine (sort of) and has a very elementary fuel injection system. I still don't know what the problem with the motor is, but if that helps you any I'm glad. I'm really interested to see what's wrong with your's because I bought a jeep to replace the maverick and its still in my back yard awaiting an engine swap :nuts: I hate this problem :fs1: I wish you the best of luck, for your' and my sake :cheers:

[Gig Pig]

It was the injector on # 6. Unfortunately the new one I picked up looks different then the others, so I'll have to wait till tomorrow after checking with the auto parts store. I even checked the part # on line & it said it was the correct one. The tops a little longer & it looks to me that the rail wouldn't fit correctly once bolted down. We'll see. Update tomorrow.

[Gig Pig]

After checking part #'s I decided it just looked different. Correct part indeed. Fixed? YES. Runs great. Have a small overheating issue I will fix tomorrow. But hopefully I'll be driving it by the afternoon. Thanks for all the help

[Eagle]

Now aren't you glad you didn't swap out that engine?

 

Of course, if the replacement engine was a used long block with injectors, it probably would have "fixed" the problem. But how much less work is it to just swap injectors?