I have a rebuilt 1.3(1990 tbi, eariler 1324 blocK), runs great but #1cyl does not fire at idle. When you pull the plug wire, no real difference in idle quality. I have a rebuilt computer, timing is correct(both ign, and cam),good spark, no vacume leaks, compression is with in 5lbs across all 4 cyl, leak down test between 8-12%. I have a 1 owner 1994 DD that I have swapped parts with, like dist, and throtle body, map sensor, egr. 3 caps, and rotors, 2 sets of wires,8 spark plugs, the cam is good and all lobes measure the same lift. I am lost, with good compression, and a good leak down, I would think that it would rule out head gasket, but I cannot think of any other problem. The plug looks like it is running lean, but I have replace the intake gasket, and can hose down the engine with carb cleaner, propane, starting fluid, and I cannot find any leaks. It does not smoke, burn oil, over heat, lose antifreeze.

WHAT THE HELL AM I MISSING!?!?!

check the cap if its a new one you have on there it mit be bad i have had lots of then be bad lately like you cant even see thatz its cracked



:massey:

i had the same problem before ,,,,,,,,,,,,
turned out it was a valve that needed to be lapped
at idle theres not enuf pressure to fully seat the valve
but as soon as you give it gas it fires on all 4 ???
at least thats what was wrong with mine
ran fine under power but shook like it had a RV cam in it at idle
hope that helps

Just for shits & giggles, Check your intake manifold mybe its pluged...

Pulled the intake yesterday, put new gasket, and yeah I checked it for shop rags and such. I would think with good compression, and an exellent leak down test, it would rule out valves, and head gasket. Yes, I have changed the cap with new, and with parts off the good running 1994. If I cannot figure it out tonight, we are going to take it wheeling this weekend as is, and if it stays together I will pull the head next week. Any other ideas?

I have a rebuilt computer

I have a 1 owner 1994 DD



Have you swapped the ECU's between the two?

Have you checked the valve lash specs on #1?

Did you check the #1 plug for spark while it was still attached? (ground to block and see if it lights up)

I have gone thru every thing I can think of. I am not a parts changer, but I have swapped everything except the longblock, and the wiring harness. I am baffled with the good compression, and good leak down test, but at this point it would have to be valve train, or head gasket. Not a big deal to replace the head gasket, but I have had this problem from the first time I started the engine. I think I will go junkyard 1.6 next time. I still have another 1.3 built the same as this one, in the box. :eek:

Ok, dumb question, but have you checked that both valves are opening?

Did a visual check, and used a dial indicator to check lift, it is the same for all cylinders. Rocker arm look fine, and rocker shaft is fine.

while its running spray card cleaner around the intake/carb you nite havea air leak that you cant hear or even find i have had it happen to me before



:massey:

Replace the plug.

Sounds like you have a cracked porcelen on it and its grounding out to the head when its installed.

I have replaced the sparkplug 8 times, tried a colder/hotter plug, switched it to the #2 cyl, and it fires fine. It is not the plug. No vac leak, replaced all hoses twice, all lines routed correctly, pulled intake to replace gasket, gasket was fine.

I am still curious as to how compression can be good, a leakdown test can be at 10%, and it will not fire. It has spark, at the right time, air, and fuel. The only thing I can think of is head gasket, or possible valve. I am not worried about it for the weekend. I would just like to hear someone tell me what would cause a miss, only on one cyl, only below 2000rpm, and how compression, and leak down, can be A+ No one I know can find the problem. If the 2tests were not great, then it would poit to valves or head gasket, but there is no measureable problem. I would never try to fix a problem by being a parts changer. Troubleshoot, find malfunction, then repair/replace. With this samurai, I have not been able to find a problem, and have 2 other good running 90up tbi motors, so I have been able to test all kinds of ideas.

So, lets see.

You replaced the plug 8 times......ok, and they fire fine in the other cylinders, OK. (at least you did not buy new plugs for nothing :D ) Did you take a spark plug reading on that cylinder? just curious if you did and what you found.


Only thing I can think of is a sticky intake/exhaust valve.....I know you did a compression check and leak down, but think about this, you may have a weak valve spring or the valve(s) may just be tight in the guide(or a bent stem), cousing it to be slow returning, and not sealing at idle, but its fine at rest.

With the symtoms you describe, at the higher rpm, the air flow would make it run better at speed than at idle.
I would look for a weak spring, starting on the exhaust side valve.


Hope that helps you out a bit.

Thought I posted what I found on the plug, it is running lean on the #1. I will switch the valve springs on #1 tonight. The valves move freely. When I get it right I will have a real well tuned 1.3. Thinking about it, the leakdown test would not show much if the valve springs were weak, because the air pressure would put pressure on the valves, not showing the weak spring.
I will owe you many beers, if it is the problem.

Sorry I thought you said it read lean, but I rescaned the post and missed it the second time....good luck

Oh and remember, that the spring length also plays a crittcle role in proper valve sealing.....if your going thru the trouble of replacing them, measure them for length and spring rate to be sure they are still within spec (if your using old ones). if you dont have a spring gauge, it should be cheep to have them checked at a good rebuilders shop.

Before ripping your head off check the ignition with a timing light. Put the inductive pick up on the #1 lead, start her up and see if you get strobing. If you are, pull #1 lead off and if there is no change then yes you might have something wonky inside. If there is no strobe, rev it up until she smoothes out and the see if you are getting the strobe now. If you do, start switching to other leads and cap locations to see if you can narrow it down, if not you might start suspecting the computer. The compression and leakdown test sort of indicate that mechanically things are in good order, with a missing spark I would suspect ignition. What maintainace or mods have you done lately ? Any unusual occurences recently, dunkings, heavy rains, bumps, bangs etc?

Before ripping your head off check the ignition with a timing light. Put the inductive pick up on the #1 lead, start her up and see if you get strobing. If you are, pull #1 lead off and if there is no change then yes you might have something wonky inside. If there is no strobe, rev it up until she smoothes out and the see if you are getting the strobe now. If you do, start switching to other leads and cap locations to see if you can narrow it down, if not you might start suspecting the computer. The compression and leakdown test sort of indicate that mechanically things are in good order, with a missing spark I would suspect ignition. What maintainace or mods have you done lately ? Any unusual occurences recently, dunkings, heavy rains, bumps, bangs etc?

Everything is fresh, the truck has maybe 1k miles since I installed the motor. I have been chasing this from day one. I have good strong spark, have switched out all ignition components, and computer, with known good units from DD. With everything I have done/checked I am lost. The l/d and compression would lead me to believe all is well, and that is the reason The
head has not come off yet. The truck was running good, but had a real bad rod knock with the old 1298 mill. I am to the point of driving it as is for the wheeling trip this weekend, it is the girlfriends trail truck anyway. I do not claim to be the worlds expert on latemodel fuel injection, but I have built 7 injected trucks including this one, the rest are sbc 350. I have a 1994 stock sami that is used as a backup to a backup driver. I started pulling parts from it just to test and have come up with nothing. A couple of friends have went over everything I have checked, and are just as stumped as I am.