Crappy idle, missing thru RPM Range, Backfire thru the intake

[T-top87GN]

I'm working on this car for a friend of mine. He bought this thing last fall. He's had nothing but trouble with it and he is ready to get rid of it. I keep telling him that these cars a REALLY finicky(sp?) and that a little patience will see him through.

Now I'm losing my patience!! Here's the run down.

All spring cleaning stuff (plugs, wires, etc...)
New chip
New coil pack
Cleaned TB & new IAC valve
New MAF (also checked with known good MAF, i.e. mine)
New O2
Fixed header and new X-over pipe (not that they matter but they needed fixed)
Checked grounds at ECM

The car idles like complete crap. It even misses up through the RPMs. It's not a constant miss. You can't find a rythym to it. I mean you think you have a good rythym to the miss, then it will change for a couple seconds on you. Then, if you load it up against the brake it will eventually backfire thru the intake.

I'm lost guys.....electrical seems fine but the lack of pattern in the miss suggets it is electrical. The lack of pattern also suggests that the miss is not mechanical in nature(maybe cam?), but the backfire suggests otherwise.

He's ready to sell me the car, and I would really like to have it (body, paint, and interior are NICE!!!). But I want him to keep this car and enjoy it as much as I have enjoyed mine. Anything you guys can think of would be great help. Thanx.

 

[TurboDave]

Ummm, let's see. Check all the grounds. Especially the ones that go to the rear of the passenger side head, and the one that runs from the fire wall to a bell housing bolt (sorta driver's side, it's braided).

Also, a badly mis-aligned cam sensor could be the culprit, you'll need to check that!!!!

 

[TurboJim]

Swap over your complete module/coil assy, (2-13mm and 1 10mm, then the 1/4" for ther plug) my bet is you got a flaky module

 

[T-top87GN]

OK guys, I'll give those a try when I get home.

Keep the answers coming guys!!

 

[T-top87GN]

OK had time to do the coil pack and module swap last night. Nothing changed. I'm going to look for ground problems next. This has to be electrical. Anyone else have any ideas??

 

[striker_29]

Bad ECM maybe?? I'm with Dave check the cam and crank sensor.

 

[Chuck Leeper]

POOR PERF??

Bandit.. You don't say the miles on the car... Hi miler and it can be the injector harness fried at the EGR base.[#3 area]. Could be the injectors are fubar. Stockers?? Intake leaks, vac hose leaks as in rotted hoses,EGR is fubar, Air intake is getting air after the MAF, cam is flat, chain is a "loose goose", YADDA YADDA ..
Have you done a leakdown? comp. test?
What kind of plugs and gap?
Scan tool readings???

Need more info and then we can proceed further.

 

[T-top87GN]

Re: POOR PERF??

Originally posted by Chuck Leeper
Bandit.. You don't say the miles on the car... Hi miler and it can be the injector harness fried at the EGR base.[#3 area]. Could be the injectors are fubar. Stockers?? Intake leaks, vac hose leaks as in rotted hoses,EGR is fubar, Air intake is getting air after the MAF, cam is flat, chain is a "loose goose", YADDA YADDA ..
Have you done a leakdown? comp. test?
What kind of plugs and gap?
Scan tool readings???

Need more info and then we can proceed further.

OK. It has 60k miles on it. I've checked for vac leaks by running the engine and spraying just about everything with carb cleaner and listening for the idle to change. I did find one leak but it was negligible and I did fix it.

What do I look for on the EGR? I'm going to check the cam with a dial indicator this weekend.

Timing chain....I doubt it but it is possible...how could I check that besides pulling off the fron cover (which I don't want to do)?

Leakdown test -- nope
Compression Test -- nope, but how would that help?
Plugs -- R43TS gapped at .035"
Scan tool looks good except for IAC counts, but since it can't idle once it gets warmed up and into closed loop I can't set the IAC anyways.

TurboJim mentioned something to me about disconnecting injectors one at a time to find out which cylinder is back firing, so I'm going to try that also.

striker_29 -- I haven't checked those 2 VERY important sensors yet but I will Friday. I'm going to see SOcial Distortion tonight so I'll be a little busy

I'll try swapping the ECM also.

Thanks guys!! PLEASE keep the ideas coming and asking questions about stuff you need to know. If I don't know it, I'll find out. This car WILL run correctly or I will die trying.

 

[Chuck Leeper]

????

EGR stuck will cause bad idle. Push the diaphram up and see if engine tone changes. Could be off it's seat w/ carbon. or the gasket could be toasted.
Low compression will cause bad idle.
Leakdown will tell you where the leak are. You can hear them.
Holes in the air intake hose?? Engine is fat when cold, goes leaner when hot and then the leak is not compensated for w/ rich idle mix.. Too Lean makes rough idle.
where is the BLM and int. when hot and idling?? O2 X counts?

 

[T-top87GN]

UPDATE!!!!!

Checked ALL grounds today. Everything is fine in that arena.

Swapped ECM, no difference.

Swapped Plug wires, no difference.

O2's show car is lean?!?! hmmmmmmm

I'm starting to think bad injector. Would a lean cylinder cause pre-ingiton?

 

[GN&aTY]

just a thought which i didnt see mentioned .. did you change fuel filter?

 

[Roger]

Another thought not previously mentioned ---- busted motor mount allowing engine to shift & short out pos cable anywhere that it could be frayed.

 

[86underboost]

i would deftinaly take a look into that egr valve...sounds like the culprit. ign module could also be it. does the whole car seem to turn off and on real quick? if so, check the + cable by the header. start the car and unplug the cam sensor....is it ok after that? if so, then i'd either reset it or get a new one. but note the car will not start again until you plug the cam sensor back in. take a look at the crank position sensor too.

good luck man

 

[Intercooler]

Well Bandit....what was the verdict?

 

[T-top87GN]

Well. That car sat in my garage until the week of the 4th of July this year. The guy stopped coming by to work on it and I wasn't going to do it all myself!

He had me come down and help him the other day and it looks like it might have a bad injector.

He's going to get a set of 30's and throw them in and see if it works.

After everything we've done on that car, it HAS to be that. O2 sensor is showing like 70mV or something. You have to give it pedal to keep in running long enough to get into closed loop.

I'll update this when he gets the injectors in.

heheh I completley forgot about this thread!