Rough idle and no power,

[ZWILD1]

Last week put in new plugs. AC rapid fire #8's along with new fuel filter ,all GM parts. Yesterday changed original O2 sensors ,car has 103,000 miles again new GM parts. Disconnected battery so computer could relearn new data from O2 sensors. I drove car for 1.5 hours and stopped. Got in to go home and car started but fired almost like an after thought. I was stopped for about 3.5 hours. Idle was rough and there was a miss you could hear in the exhaust. This morning car starts ok runs smooth . Turn it off after 15 minutes and when I start it again rough idle is back. At about 78,000 I had a coil go bad which seems to remind me of how it ran with a bad coil. I replaced all four coils and plug wires then that was two years ago. All 8 are firing now but sounds like cracking or knocking under plenum when I pull some of the plug wires while it is running. So I pulled the plenum I don't have anyting to test wires or coils. Thinking of replacing coils and wires, I have new wires, If I could find out if a coil went south I would use one of the good originals I saved. Has anyone seen this sort of problem before. I will say I have felt like something has been going on for a few weeks. You can just tell by sound and feeling. Not as strong just alittle off.

[tomtom72]

Hi, The 'knocking' you hear is the dual mass flywheel most likely responding to the miss.....it can sound like a diesel if the miss is bad enough. The noise from the d/m/flywheel also sounds like a very bad rattling.

I guess you checked the plugs for fouling?...or if they are too clean? I have heard about people having failure issues with aftermarket coils but the OEM stuff is usually reliable.

Just a shot in the dark....if yours is a 90-91-92 the OEM injectors fall pray to the ethanol in the gas today and in the early coil failure stage exhibit a ' slight miss' due to the gas shorting the coils...the ethanol eats the early epoxy insulation....the miss usually gets real bad real quickly though as once the insulation disolves things go south quickly.

You can ohm out a pair of wires + that coil by reading the ohms from one plug end to the other thru that coil assigned to that pair of wires...or you can just use a spare plug and pull a wire and give a look at the spark intensity, they show a strong arc when tested that way...no mistaking a good wire & coil it's a strong visable spark even in daylight.

On the injectors, if they are bad enough you can smell a lean condition thru the exhaust. Also, usually till the coils get real bad, upon start up from cold they work okay. It's not till the coils get hot that they start to short out & cause a miss....it almost seems that there is no miss at cold idle, but it is there but very slight & it gets worse as the coolant temp comes up.

This is another shot in the dark, the MAP hose is okay? No oil in it...that's bad for the MAP sensor....and it's connected, they blow off sometimes if the motor backfires.... sorry I'm not trying to be a wise guy, but that will cause a miss too.

Miss plus the weak starting (not hard starting like it's flooded) usually leads me to check the ingnition first but you have that covered.....unless ya closed a gap upon plug installation....(again not trying to be a wise guy).....but with the early Z's the injectors were never intended to work with ethanol, so they become a prime suspect. Oh yea almost forgot...vacuum leaks, large & a bunch of small ones will make for an ill running LT5. Check the entire PCV system for cracked rubber fittings...ya know over time & all.

Forgot this too....fuel pumps PSI, and the strainers (socks) and check the regulator hose for gas. With the plenum off you can see if the spray is okay or if some are weak/not spraying....and you can ohm the injectors but cold usually they ohm out okay unless they are really bad, but then that = a big miss.


Tom

[ZWILD1]

I am going to check OHM's on the injectors ,as they are the originals. The coils should be ok as I replaced them about two years ago. All plugs seem to be firing or at least have spark. Don't think it would hurt to replace injectors as they have 103,000 on them. I will test the wires also.

[tomtom72]

ZWILD1,

I saw your other post in the rough running thread. It is not a good sign if the plugs look like they just came out of the box....all white & pure looking. That's what the plugs in my car looked like when I had injector coil failure, no squirt, no gas, = clean plugs, too clean to have seen any combustion. I had all four right bank primaries go down at once so I could smell the lean condition at the right exhaust as well.

Pending a scan of the motor running in closed loop, I think the injectors might be the #1 suspect at this point in time.


Tom

[ZWILD1]

I did a ohm test of wires and coils. They all look good. Injectors on right bank #2 primary and #8 secondary cold 9.5&11.4 . Left bank first 3 injectors all mid 6's cold looks like time to replace them all. Haibeck recommended accell #150821 from summit racing.

[Z51JEFF]

Injector time.I just got my car back together.I used the Accel injectors.There a guy,Jon? at FIC that sells a complete set of rebuilt injectors for around $350 for the set.Havent heard a single bad thing about the guy or the parts.In fact when I first started looking into replacing mine I called the guy.He was ready to send me the injectors.Tells me,put them in the car,if you like them PAY ME FOR THEM,if not send them back.How many people do business like this?Not too many.

[ZWILD1]

FIC who's that. Sounds like a deal. Did you have to modify the connectors to do the install. I have everything tore down just need the injectors. I'm chompin at the bit going crazy .

[karterdon]

i would not recommend rebuilt injectors - If you don't like them - That means tht you are going to pull the plenum again - Not worth it. I have the accel's - Only a very slight mod. needed for the alignment peg on the injector - So that the connector can push on - Only needs to be done on 8 of the injectors - A small file and a few minutes per injector - Your then good to go. I would go with what Haibeck say's. You won't regret it !!

[ZWILD1]

I ordered injectors from Kurt White. Just drop them in they are the Accels.

[ZWILD1]

Today I removed the injectors and the fuel rails. I discovered that the PCV hose that holds the valves had a large split on the drivers side, almost clean through. I was able to repair it until I get a new hose. Now I have to call Kurt again to order the hose. I can't wait til I get the injectors and put the car back together.