AirCOOLme

i have a 79 3.3L with sc cams and 8-1comp its in a 77 with only the CIS pump up front..

it was rebuilt 6000miles ago.

at idle and part throttle under no load cyl # 5 fires intermittently.. sounds like a exhaust valve not seating but the heads were rebuilt.

also i have cold start issues, the car will start on only a few Cyl at first, and idle at 700rpm.. then a slowly climb to 950 as other cylinders come on.

the weird thing is 1 in 10 starts it will jump right to 1200 and be firing on all six.. sounding wonderfully... but after a minute or two it will drop to 900 and start coughing again..

i have\had..

mixture at 13.5 idle and 10.9 under boost,the fuel distributor rebuilt, fuel injector checked(not GREAT but ok), fuel lines switched,Don Jackson's went over the fuel system, spark plugs changed, plug wires swapped, leak-down 3%, control pressures checked, vaccume leaks checked\fixed

adjusted valves last 4000 miles ago(my first time.. my mechanic is now re-adjusting them ito see if i screwed up.. )

Any ideas why it breaks up at idle and when under no load? i need all the help i can get..

thanks - nick

sand_man

I feel for you...this is where it can get tricky and frustrating: diagnostics. Is it fuel or is it ignition? In my case, I took my engine to about 7,000 RPMs with no load to the wheels after my original rubber centered clutch let go. I quickly got off the throttle. The car would still run...just not move due to the broken clutch. I removed the engine/tranny and replace all of the clutch parts. However, the engine never ran the same after I finished the job. Felt like one of the cylinders wasn't firing. Sounded like an early VW Beetle or a Harley. There were no exhaust leaks, the spark plug firing order was correct, and each plug was getting power. I made an assumption that I must have broken a Dilavar head stud. I figured now would be a good time for a total rebuild. The engine leaked enough oil to solve an energy crisis, so what the hell!?

As I tore down the engine, the head studs were fine. Nothing was broken internally either. I discovered that nearly every one of my fuel injector manifold blocks was seriously cracked! Also, one or two of the fuel injectors looked to be in pretty bad shape.

In hindsight, I think my poor running engine problem was either caused by the timing chains jumping a cam sproket tooth from the engine going from redline to zero in a matter of miliseconds (hydraulic tensioners have been known to cause chain slack under extreme conditions), or a cylinder not getting fuel (faulty injector), or an intake leak (cracked injector block).

Don't mean to be so long winded here. Just wanted to share my experience.

PorschePhD

Have you done a leak down or a compression test? I would do this first to rule out something strange.

Have the injector spray pattern been checked? Have the WUR control pressures been checked? Fuel accumulator is holding what pressure after 20 minutes rest?

Who rebuilt the fuel head?

Lets see if we can't help here.

AirCOOLme

Thank you all very much for trying to help! i am totally baffled by this!


i pulled the plug lead to number 5 and i think thats the cyl that is misfiring because pulling it has very little effect at idle... the idle sounds the same but it starts to backfire..

that was the only cylinder that i did the compression and leak-down on. I cant remember the compression numbers but the leak-down was 3%.

I had don Jackson enterprises (in Phoenix) pull the injectors and bench them. the cracking pressure was fine and they said they were not great.. but sprayed "ok" not enough not to cause a problem. I will get back on the phone with them and get more info. I do not know how to test the injectors on my own with the metal lines... with plastic on my early SC i was able to pull them all out and aim them into a bucket!

i have not checked the fuel accumulator for holding pressure. or i might have and cant remember (i have been working on this for a LONG time) i will check the record of what i have done tonight.

the fuel head was rebuilt by Fuel Injection corporation. It was rebuilt when the motor was.

During the process of troubleshooting i cracked the #5 injector line (the banjo fitting)at the fuel head to see if i had fuel pressure and it did not "spert" like the rest of them when i cracked the line. Also there was no change in idle(indicating a dead cyl) so i sent it back to FIC and they put it back on the bench.

i was called by there "senior tech" and told that there is nothing wrong with it. So i put it back on the car and nothing changed...

it will be so nice if i can solve this... .. 3 months of attempted diagnosis is driving me nuts!

dyerkes

Nick,

Your fuel line has enough "give" in it to allow you to pull your injector to test fire it in a bucket. Another option you can try is to take the number 5 injector and swap it to another location and see if the miss moves to that cylinder. If the miss still occurs on #5 then you know that it is less likely to be the injector.

David

AirCOOLme

thanks for the tip david... i know i switched injectors and im pretty sure the problem stayed with the cyl.. i will have to check my notes when i get home.

another spray pattern test is in order..

thanks!

AirCOOLme

yep, checked my notes.. swtiching injectors the problem stayed at 5... the pressure was checked for 2 hours.. held just fine..

have not spray tested yet but Don jackson's did bench test them


any more ideas?
-nick

srf506

Stuck/burnt valve? Just thinking out loud here.

PorschePhD

Check the valve adjustment on # 5. I wonder if it is too tight. What was the compression test? Did you do a dynamic compression or static?

AirCOOLme

don't have the compression numbers on hand but my mechanic said they were right on for 8-1 compression.. if you need actualy numbers just let me know...

dynamic(if thats me cranking him at the back of the car reading)\


I will re-check the adjustment

PorschePhD

No, Bosch recommends dynamic as apposed to static. Pull the pull and place the compression tester in the hole. Start the car and see what the gauge does. You will be surprised what happens when running and under pressure. Compare those numbers across the board

jwl

Stephen,
What are the specs for the WUR control pressure and fuel accumulator?

AirCOOLme

the compression tester was in the hole and I hit the ignition key... isnt that dynamic? the fuel relay was pulled so it wouldnt start..

am i missing something? sorry im knew to this!
thanks -nick

PorschePhD

What year and what WUR number?

PorschePhD

Don't apologize, this is how one learns. Nothing with not knowing and asking. EVER.

No, that is static. Starting the car and it running with the compression tester in it is dynamic

Bet most have not even heard of this!