Engine miss, exhaust? rough idle, Help Options

[DarrenG]

Back again with more issues.

About 500 miles after rebuild, the 2056 Djet is having issues.

It started with an engine miss. Ran, just rough. Brought it home and parked it for a couple of days. Started it up, ran fine. Perfectly smooth at 2000 rpms for about 2 minutes, then the idle dropped to 950 and the engine started shaking like it was missing again.

I put a hand over the exhaust and you can hear a hiss. I couldn't find where.

Any thoughts? Suggestions on where to start?

Thanks

D

[orange914]

run a compession check to isolate any cylinder/mechanical issues.

did you do anything to your d-jet to accomodate the extra cc's? what compression are you running? what cam and oil/additives-how did you break in the engine?

[DarrenG]

run a compession check to isolate any cylinder/mechanical issues.

did you do anything to your d-jet to accomodate the extra cc's? what compression are you running? what cam and oil/additives-how did you break in the engine?

No changes to the DJet (did have to replace the MPS though - bought a rebuilt from Automotion.)
CR - not sure. friend helped put it together. we made sure everything turned freely. skipped the head gaskets. used the slip in 96's from AA.
stock grind cam from CB Perf
no oil additives. 20/50
break in was 2000 rpms for 20 minutes - saw that somewhere.

I'll run a compression test this weekend.
Thanks

[Cap'n Krusty]

Increasing the diameter of the piston and cylinder increases the compression. Leaving out the head gaskets increases the compression. Any time you make changes like this, you MUST measure the combustion chamber capacity, measure the deck height, and calculate the compression ratio. You then adjust it to suit the fuel you're gonna run. Failure to perform this task can (actually, WILL) result in too much compression, making too much heat, and causing a greatly reduced engine life. It could be as little as 500 miles. I've seen less. Increasing the capacity and the compression could have leaned the engine out. More heat, more likelihood of damage. FIRST thing you should do is adjust the valves, then warm the engine up and do a compression test. Report back.

The Cap'n

[DarrenG]

[FIRST thing you should do is adjust the valves, then warm the engine up and do a compression test. Report back.

Reporting Back:

Adjusted the valves today. I and III were loose - worse on the intake. II and IV were close.

Compression check (brand new tester):
I: 140
II: 140
III: 130
IV: 140.

Still has an intermittent knock (sounds like a slap to me).
Still sounds great at times. I can take it to 4000 rpm and it's smoothe, with an occasional buck, but maintains the rpms.

After it's warm and I let off the throttle, it drops to 950 and shakes - clearly a miss.

Injector?
suggestions?

Thanks again

[DarrenG]

Getting closer:

The injector on III is not getting power. I switched the injectors, so I know it's electrical. More homework required to figure out why.

Hopefully back on the road in a couple of days.

D

[arvcube]

Getting closer:

The injector on III is not getting power. I switched the injectors, so I know it's electrical. More homework required to figure out why.

Hopefully back on the road in a couple of days.

D

Pull off that entire harness and make all the necessary repairs. I had the same issue when I noticed the same symptoms. Instead of buying a new harness from Jeff Bowlsby, I cheesed out the cheap bastard way and fixed mine. No issues anymore...

[DarrenG]

More homework:

Injectors II and III aren't firing - so it's trigger points.

Before I buy another new set, does anyone have any idea why trigger points wouldn't be working after only 500 miles?

Is there another potential cause for injectors II and III to not fire? I think it's intermittent, because at some speeds it sounds fine.

Thanks

D

[ArtechnikA]

Before I buy another new set, does anyone have any idea why trigger points wouldn't be working after only 500 miles?

If they were new with the engine, could be the rubbing block(s) weren't lubricated and at least one side is worn out. Could be one side is contaminated and there is no conduction. In either case, the other side is probably not far behind it...

Is there another potential cause for injectors II and III to not fire? I think it's intermittent, because at some speeds it sounds fine.

connector at the trigger point module. wiring harness open. grounds.

You verified 'not fire' how, exactly? Scope? (Absence of) fuel spray? There are other reasons to explain why you''d get no spray. If you've verified no electrical pulse to the injector, you have to fix that first...

[DarrenG]

You verified 'not fire' how, exactly? Scope? (Absence of) fuel spray? There are other reasons to explain why you''d get no spray. If you've verified no electrical pulse to the injector, you have to fix that first...
[/quote]


I was mistaken. Trigger points were not replaced.

I and IV squirted fuel, II and III did not. When I switched the plugs to the other injectors, II and III squirted, I and IV did not. It's not the injectors.
Thanks

[dw914er]

at this rate, i would probably replace the trigger points, the condenser (could be bad, hurting the trigger),distributor, ok, most of the basic electrical stuff. This way you can make sure you are getting the right spark for each cylinder. I suggest that because its happened to me, and that worked