Help with 1991 Lumina Euro

[bradleyz34]

Hello. I have a 1991 Lumina Euro 3.1, A/T, with 230,000 miles. The problem began a few months ago with a few light 'bucks' at about 60mph. It went away. Then it would run fine for days. Then the 'bucking' would come back at any speed, a few here and a few there. About a week ago the bucking became very bad, to the point the car would shut off while driving. Yet, I would pull over, and it would fire right back up, I would take off, and the bucking would start all over. It would buck at all speeds from 5 mph to 70 mph. At faster speeds it would stay running a little longer. The bucking became so bad I could only drive it about 500 feet before it would shut off. My task was to drive it 70 miles to my uncle who is a mechanic. The first 35 miles it bucked the whole way, then it ran like brand new the 2nd 35 miles, which is natural because of course then he could not really see the problem. Well we fixed the spark plug cables because those were wore through and we thought maybe they were arching and then we changed the fuel filter. The car started right up and ran real nice. It was making some clicking noise by the engine though, we shut it off and could not get it started again, it was getting no gas. So we took off the fuel tank, and the fuel pump was absolutely dead. We put a new one on and it ran great. My parents are driving here because i have their car and they said after about 20 miles, it bucked about 3 times and almost stopped. So they called my uncle and he said bring it backm well then it ran real smooth so they turned arournd and started back here, and its ran well since. So my worry is that its just history repeating itself. It ll buck a few times and drive nice for a few weeks, then just go to absolute shit. The spark plugs are pretty new, the coils and module were recently replaced. it has a new fuel pump and filter. The injectors all checked out last time, it has a new fuel regulator, vaccum hoses are good, spark wires are new.

What could be causing this weird bucking?

[maxwedge]

Until the condition becomes worse or it dies and will not start it is very tough to pinpoint the problem. I assume you replaced the fuel filter when doing the pump. If it dies both fuel pressure and spark should be tested during the no start event. Pcm could be an issue, crank sensor, ign module all are in the loop with these symptoms.

[bradleyz34]

UPDATE*!*!*!*!*!*!*!*!

After a new fuel pump, spark plug wires, fuel filter, the lumina ran well for a few hundred miles. Last week it bucked once, then it started to buck more and more. Now its bucking several times. Whatever the problem is, it took it awhile to restart. IS this a case of a bad fuel injector???

[maxwedge]

Anything is possible, a misfire can be caused by a multitude of issues, yes an injector is one, as is plugs, wires, coils or a lean mixture are the most common ones.

[DnaProRacing]

I just got injection service done and it made a WORLD of difference. no more hesitation, no more burps, and the newfound power amazes me. I didnt know this car had such big B*lls! ofcourse i've had alot of other stuff done to it, but I strongly suggest getting this done! cost me $116 at pepboys. the tech told me i had a ton of carbon buildup in a couple of them. i knew i had to get it done, glad i did it...
im leaning more toward the knock sensor in your case. specially if its killing the engine while doing 50+mph. can you restart it in nuet when it does this???

[maxwedge]

A knock sensor cannot " kill" an engine, it controls spark advance thru the pcm , at best or worst some power may be lost or pinging would be evident at either extreme of a malfunction. You need to rethink this advice.

[DnaProRacing]

sorry bud. just guessing at this point. since he's done just about everything else. like me, i basically replaced "everything"...
that is how i fixed mine, doing everything that everyone suggested testing and fixing. took some time but finally got things running right.
I was told you had to be either a mechanic or rich to keep these lums running. and now i can honestly say "they're right". I would be scared to death if my car cut off doing 50+. replacing all the sensors and checking the wiring would be the first thing i would do. my car has gone thru some crazy things, they seemed to come and go and NOONE could ever put a finger on the real problem. i started with the obvious, then moved onto things that had nothing to do with the symptoms, some things cured certain issues, some didnt. so like i said, i replaced just about everything. the exciting part is "whats next"? thought i read in another thread that the knock sensor could cut the engine off, my mistake. cant believe everything you read on here. I will do some more research for him and see what I can come up with. thank you for correcting me...

[bradleyz34]

Heres the latest. Drove it to my parents so I could have my uncle look at it (mechanic). 75 mile drive, right out it started bucking terrible. THen it settled down a bit after 20 miles or so, with an occasional buck. Ran ok. Was going up a hill with about 20 miles left and kicked it down, RPMs shot up to 4000, but it had no power, didnt want to speed up, took about 1/2 mile to go from 55 to 65, then bucked a bunch and killed. got it home, my dad and i took it out, ran ok, sped up to 65ish, and it bucked a few times, almost killed. Took it to my uncles, he tested spark, all plugs have nice spark, he pulled one spark cable off and the engine didnt even slow. engine always has had a dead miss. starts up nice, after about 1 minute of idle runs rough, We re thinking dead injector. It never killed before or bucked this bad.

[4x4 blazerguy]

It isn't throwing any codes? It should be. Is the fuel tank clean? could there be crap in the bottom that is clogging the pickup (some of the time) on the fuel pump? What is the fuel pressure? You said you put on a modular? Did you use the heavy electrical grease on the heat sink? Blazers are great for having problem because of that. Even the HEI GMs distributors clear back into the 70s had problems if the grease wasn't put on. Just some areas to look.

[bradleyz34]

its not the fuel tank. When we changed the pump we put a new tank on, cause the old one was broke. it did this with both tanks. THe spark mod isnt that old, and it has great spark.

[Bearwulf]

First of all, the OBD1 system does not list codes for injector or IM problems. Check ALL grnds for good contact, especially those from ecm. Do not discount IM as the prob., even a new one can be bad. Maybe pull ECM & send in to have circuitry tested (most shops do not have equip't. to make these tests), try to find ECM from good working car(same year & options) to swap into yours for test drive. Remember to change PROM from your ECM to the other one for this test.

[bradleyz34]

Well, it appears to be fuel injectors. My uncle took them off, one tested at about 8 ohms, and one was testing odd. It wuld test different everytime. From 8 to about 10. He said hes nbever seen anything like that after changing tons of them. It seems to run fine now

[maxwedge]

Ok they were tested, reinstalled , but was done to correct the problem?

[Bearwulf]

He didn't say they were reinstalled.

[bradleyz34]

ya, we put in 2 new injectors. it seems to have fixed the problem