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Discussion Starter · #1 · (Edited)
I bought my 1994 Caprice wagon from the orginal owner after it had been sitting for 18 months. He left it sit when the waterpump started to leak and the price to repair it and whatever was now causing it to miss as well as a bad starter and flywheel was too expensive.

I replaced the starter, water pump [including a new thermostat and coolant temp sensor] and opti [off eBay] just to see if it ran. I didn't bother with seals or anything, I just wanted to get it going to see if and how well it ran or didn't run. The original opti cap had the #2 cap snout broken off so I had to do that anyway. I figured I'd be opening everything back up anway so..... I got it to run, it ran pretty good but had a miss sometimes then would run like it should then back to missing and backfiring again but it had a 3/4 tank of old stinky gas and I figured the plugs and wires needed done too.

Okay, then after the first month of working on it [had little time and worked on it when I could], I began wondering if I'd ever get a title since the guy had to apply for a duplicate and kept giving me every excuse it the book as to why he didn't have it yet [had to get the DMV inspector involved]. Well, that fiasco evolved into 4 months of waiting due to the original GMAC lien that needed released and GM kept screwing up the MV paperwork and I refused to put much more effort, time or money into it until I knew I would get a title.

Got the title last month so I got some parts ordered; Fuel pump, sender, strainer, filter, in tank harness, EGR gasket [cleaned EGR], GM opti, good quality plug wires, plugs, necessary seals, etc... and went to work. I replaced the fuel pump sender, fuel pump, strainer, fuel filter, in tank harness etc... because the fuel pressure was a little low [38 key on and dropped when throttled] and I did it twice because the 1st Walbro copy pump didn't pump. I got 43PSI with the 2nd pump and thought maybe this was part of the sputter/miss/backfire] problem.

Nope, so I went ahead and installed a new GM opti with new seals on the timing cover [stopped the nasty leaks], plugs, plug wires, coil and cleaned the EGR and MAF. Okay, now it still ran the same, started right up but idled rough, spits, sputters, backfires and has no power. I checked everything 10 times and it's right. I took my time and did everything very correctly to be sure it was right. Today I installed a new opti electrical harness that I was assured would solve the problem but................. nope!

I even spent the last week refurbishing the 9C1 wheels I got with new paint & new center caps anticipating a late weekend ride!

It will idle all day long, albeit roughly and there's a random exhaust backfire out the passenger side tailpipe. No rhyme or reason, just whenever it feels like it. If I throttle it up it hesitates a second then gradually increases with a notable intake backfire progressing to an exhaust manifold backfire but then it will even out and actually sound quite good above say 12- 1500 RPM's but backfires as it comes back down to idle.

NO CODES

What's next? O2's? New MAF? TPS? IAC? ICM?

or a grenade?
 

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Discussion Starter · #2 ·
I don't know how I forgot that I did the AIR pump delete too, just to clean up the engine bay!

Oh, I also removed the K&N oiled air cleaner, cleaned the air box, plugged the AIR tube hole and installed a new paper air filer.

I've spent a few weeks getting greasy, sore and I'm still where I started. I wanted to replace a lot of this anyway as maintenance items but without the rewards of running better it's disheartening :(

I've read the countless posts that all end without closure. I assure you if I figure it out, I'll close the post with my outcome, even if its a video of it becoming a new artificial reef :)
 

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How many miles are on it?

I'm sure others will post but I can tell you when I had a bad ICM basically car would NOT even start or run when warmed up so if it idles somewhat it might not be that...
As far as IAC and Coil (I didnt see you mention replacing it?) both you can test with a multimeter:
http://www.shbox.com/1/coil_testing.jpg
http://www.shbox.com/1/iac2.jpg

If its got miles 100k mi or more DEF replace O2s

Also once on my old 96 impala ss after doing headers the ceramic was cracked on one of the plugs probably during install of the headers and symptoms were that the car idled somewhat rough and at lower rpms but if you got on it, it went away...figured it out by pulling fuel injector plugs one-by-one until I found one that when removed didn't noticeably make it idle more poorly, i.e. on that cylinder either bad injector or plug and in my case turned out to be bad plug...
 

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O2's would be my guess. DO NOT get the german crap...A/C delco only. Does it matter if it's hot or cold? Get that old gas outta there.
 

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Discussion Starter · #5 ·
178,000 miles

I've read that ICM issues are usually post warm/heat up related.

Coil is new.

Old gas is long gone ~ I emptied and cleaned the tank when doing the fuel pump work.

I see a lot of posts about the O2's and similar issues. I never figured they could cause such symptoms but.... I've read about not using Bosch and won't.

I'm going to double check all vacuum hoses, check for vacuum leaks, etc... too.

It starts acting up immediately from a cold start and it doesn't seem to make a difference as it comes up to temperature.

Thanks guys!
 

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If it does it from a cold start, it might not be the O2s. They only come into play once the system enters closed loop. Does your fuel pressure hold when its off? You could have a leaking injector, or one thats intermittently firing. I would also check the injector harness to see if anything is loose.
 

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Discussion Starter · #7 ·
If it does it from a cold start, it might not be the O2s. They only come into play once the system enters closed loop. Does your fuel pressure hold when its off? You could have a leaking injector, or one thats intermittently firing. I would also check the injector harness to see if anything is loose.

True and my thoughts as well ~ it acts up from a cold start.

I was yanking on the FI harness when fitting the Corvette fuel rail covers [still not on yet] so maybe I should start there. I mentioned this before but I've done so much that I forget when and what I've done [old age maybe?]!

I did spend a few minutes this a.m. before it got blazing hot yet again and found a pretty badly cracked elbow at the front of the intake, passenger side. I really didn't get much past that to even see where it goes before I needed to get going.

I had it running decent intermittently a few weeks ago. It would stumble and run like crap then take off like lightening.

The last I checked fuel pressure is when I did the pump, it was great and held well over an hour. I hate even thinking about checking that again in fear something is up with that mess.

When my fuel pump went out in the Suburban it acted much the same. When/If it would start it had a rough idle, it would spit, sputter and backfire...........
 

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Discussion Starter · #8 ·
Okay guys, I spent about an hour checking stuff this evening and I think I'm on the right track now. I put my fuel pressure gauge on and got 45 PSI w/ key on/engine off. As soon as it pressurized I could hear a passenger side injector leaking [I previously thought my fuel pressure tester schrader valve connection was a little loose] and as soon as my wife released the key the pressure dropped to 35 but it held pretty steady therafter only dropping to 33 after 30 minutes.

Also, I pulled the dipstick and it smells of fuel. My wife said when I started it yesterday it belched black smoke for a little while [running rich] ~ my head was under the hood so I didn't see it and I didn't want to start it tonight.

So, it looks like I've got a leaking/flooding injector. I'll get the rail off and install a set of new ones soon and see what happens [fingers crossed].

Thanks to everyone, especially 95BRMW who opened my eyes mentioning the injectors. I was offering help to another forum member with a similar situation and never even considered it to be my problem [hopefully].

Next question......... what type of injectors are others running on a stock engine?

Any recommendations?
 

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Just get another set of stockers. They work fine up to around 350 whp or so. Depends on the tune and intended use. I cannot remember the name of the guy in NJ i used to use. I'll try to see if he is still in business. Would rebuild, sonic clean and flow check injectors to within 3 % and for a few bucks more would get you a set that flowed within 1%. Makes worlds of difference.

Chris
 

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Discussion Starter · #10 ·
Just get another set of stockers. They work fine up to around 350 whp or so. Depends on the tune and intended use. I cannot remember the name of the guy in NJ i used to use. I'll try to see if he is still in business. Would rebuild, sonic clean and flow check injectors to within 3 % and for a few bucks more would get you a set that flowed within 1%. Makes worlds of difference.

Chris
Thanks, I value your input!

Here's a photo of the old girl I took this morning.............. jut begging to take a little spin :)

 

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Discussion Starter · #11 ·
I finally installed another set of cleaned/rebuilt factory type injectors today and changed the oil but it still runs like crap, maybe just barely a little better.

It had a K&N oil soaked filter in it but I removed & cleaned everything, including he MAF before putting a plain paper filter in months ago. If I unplug the MAF it almost dies but stays running and evens out but acts the same way otherwise. Maybe the MAF was damaged by the K&N stuff?

Maybe try a new/good used MAF?

Idle is good [not high like a vacuum leak] and idle exhaust backfire is gone now but can still hear a miss in the exhaust. It stumbles off idle [with backfire in intake] then revs good above 2000 RPMs.

Much better in park when idling, in gear it's very noticible. I haven't driven it and don't intend to.

?????
 

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My strong advice is to get some new AC/Delco AFS 75 Oxygen Sensors in her. They definitely could still be your problem.

I had a set give me all kinds of intermittent fits on my '94 Roadmaster Wagon (@ ~100K). I was trying to drive to FL from IN (with my family) and made it about 350 miles on the third try (I replaced a number of other things on the previous two tries) when she started spitting and backfiring again and had to turn back again; about 30% of the time running on the way back (300 miles) she spit and popped (a number of backfires too), barely get over 45 mph... oil took on a fair amount of gas and I was worried about engine damage. Got into work (Delphi in Kokomo (where all the GM automotive electronics are done) and borrowed the Tech 1; showed O2 codes. Put new AC/Delco O2 sensors in and 'that was that'.

You have 175K... PLEASE get rid of those old O2 sensors! They really are a maintenance item!

Kevin.
 

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And, don't forget to put in a new opti vent hose... if you have not already done that.
 

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Discussion Starter · #14 ·
Vent hose is new.

On advice from the LT1/LS1 board as an o2 test, I unplugged the o2's and gave it a shot [o2's look real good/recent by the way].

Same old, same old.....

It idles pretty good [maybe a little better than last time] and rev's decent in park/neutral but under load it bucks, pops/backfires and sputters like crazy.

The MAF was coated with a film of oil from the old K&N filter. I cleaned it up a few weeks ago with the correct MAF cleaner hoping that would help but no change so maybe MAF ???

It seems like an bad EGR symptom but it checks out okay and I did clean that up a while back.

I'm about to give up.
 

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Discussion Starter · #17 ·
Just checked the "engine sensor" fuse as advised may be a possible cause, actually checked all fuses inside and out but none are blown [and no specifc "engine sensor" labeled fuse].

Frustrating as heck.
 

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Discussion Starter · #18 ·
Someone else posted on another forum:

"it starts choking and chugging and when i gas on it, it starts to backfire and the valves rattle."

Reply:

"I had the same problem on my 94 LT1.... turned out to be the fuel pressure regulator...the rubber diaphram leaked under load at idle, otherwise it ran fine. no codes as well I hope this helps?"

Could it be?

I saw no obvious signs of a FPR problem or leak.
 

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Discussion Starter · #19 · (Edited)
Got an early start this am and put my fuel pressure test gauge on it.

Key on/engine off ~ gauge pegs 43 PSI instantly but as soon as the pump finishes priming the needle drops to 40 PSI then actually starts to rise 1-3 PSI, settling within 30 seconds at 41-43 PSI on several attempts.

Start ~ at idle gauge drops to 35 PSI and when throttled up it goes up to 43PSI at about 1/2 throttle.

Pull vacuum line off FPR ~ it goes to 45 PSI

It has not leaked down [dropped] in 20 minutes now.

#'s seem normal.

EDIT: Oh, I've only started it a few times since changing the oil due a gas smell in the oil and now it smells like gas in the oil again!

I'm 99% sure the replacement injectors are fine and there's no sign of leak down.
 

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Discussion Starter · #20 ·
Just pulled the o2's out completely to check for a possible clogged cat and although louder, it's still the same.........

The o2's were sooty black. They look to be in great condition, appearance wise and not too old for sure. They are ACDelco's.

That post from another forum I posted about the FPR causing an issue without any real signs of being bad [and the same symptoms] has me wondering.
 
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