Rough engine/lack of power – 1994 Buick Roadmaster

[Kevin]

Hi all — long-time viewer of Eric’s videos (first brake job I ever did :)) and now could definitely use some assistance with my 1994 Buick Roadmaster (Sedan, 156,000 miles, automatic transmission — one of the B-bodies with the LT1). I am nearly to the end of my “expertise” and starting to get worried. It is running rough and experiencing a lack of power at higher speeds and when hot.

I tried to organize this into two parts…the first section (1-7) is the symptoms and behavior with a bad fuel pump giving 18 PSI, and the second section (8-13) is the symptoms and behavior with a good fuel pump giving 40+ PSI. You might just be able to read the second section (8-13) and figure it out right away but I included 1-7 incase it helps…some problems were more pronounced with the bad pump. Sorry for so much text — hard for me to tell what is important or not, and I do not want to accidentally exclude something which means absolutely nothing to me but the world to any mechanic.

I also included some audio of how the car sounds when stopped in different gears (see #12, below…this is when it had the bad fuel pump) and with the AC on and off. It sounds the same with the new fuel pump but a bit richer and harder to hear clearly.

With bad fuel pump, 17-18 PSI instead of required 41-47 PSI:

1. Two weeks ago I came to a firm stop and Code 44 (lean exhaust condition, left side of engine) SES came on about 30 seconds later. I could effectively prevent the SES by giving the engine an extra 100 RPM every 35 seconds (code remained, just no SES). The engine was rougher and had less power when this code was lurking, even if not on. Worse when hot, MPG over that 4-day period was near 15 and usually is 19-23. On the last trip I took (highway) I got a “too good to be true” 24 MPG. Engine compartment SEEMED 20-30 degrees hotter than usual, could be my imagination.
2. O2 sensor tested bad so replaced it and spark plugs (going to OEM plugs away from double-platinums), and did elective maintenance of new plug wires, two new vacuum lines, oil change and replacing the second O2 sensor. Accidentally misrouted two spark plug wires on the right side of engine during this time and drove it for about a mile that way before identifying and fixing. “Knock sensor circuit short” code 43 came on after idling for a bit a few hours later, no pinging or knocking so decided to ignore it for now since knock sensor wiring looked good and it drove quite well. (Stupid risk, I learned afterward.)
3. Car drove better than I have ever seen for about a mile (“fixed!”), then roughness came back gradually over a 16 mile period. If you have ever tried to hold a spinning washing machine still with your hands and felt the force push on your hands on each rotation of the washing machine – it felt like the engine was doing that when I gave it gas. Subsequent “hold brake/push gas” tests had the same feeling even with the small amount of gas I provided the system. I pulled over and spun the knock sensor wiring around and the car drove much better, but still rougher than before the maintenance (see #2 above). I think this better performance was due to letting it cool down, not spinning the knock sensor wiring.
4. When I would come to a stop, for the last 6 MPH of slowing the engine would begin threatening to die as if it were running on fumes. When I was fully stopped it would continue this chugging, and when taking off it continued until – I think around 10 MPH. With the AC off it barely did this at all and was almost smooth, and in neutral or park it was nearly smooth. AC on/off had no impact after it was at 10+ MPH.
5. The next morning I found that it ran better (still rough but not scary). I found out that it lacked power, and all of this felt like what I know of vacuum symptoms, so I double checked everything. The check valves to the distributor were reversed (we replaced that vacuum line); car drove really great again (“fixed!”) for maybe half a mile, then became rough again. The knock sensor code was gone at the next startup and no codes since then.
6. I discovered that as the car gets hotter, it starts having a severe lack of power and runs rougher. (RPM the same.) At seeming random I could smell exhaust.
7. Drove it back to my work area which is about 30 miles away. This trip was similar to #3, above, but this time it started out bad and became horrifically bad after around 12 miles – the spinning washing machine was back. Pulled over, tested fuel pressure with the gauge I bought. 12 PSI key on/engine off, should have 41+. It was 17-18 PSI when started, and it dipped by 1 PSI each time the engine felt rough.

Now, after the fuel pump replacement…

8. Installed new fuel pump (ScannerDanner’s hour-long video here: https://www.youtube.com/watch?v=RyEPOeQB0Zg did the trick even with just a volt meter, great reference!). New filters and old one was clogged. Fuel pressure regulator and overall pressure test out fine now.
9. Now when the engine is cold, or at lower speeds, I have great power, but the rough engine operation is still there and seems rougher. Once I get up to 50 MPH+ I begin experiencing the same lack of power behavior as before the pump replacement. With the new pump I can at least accelerate to some degree but it is still extremely weak once hot / up to speed.
10. I discovered that now, if I give it a good amount of gas at higher speeds, it will go into passing gear where it smooths out quite a bit. I still do not have power in passing gear but it feels smoother.
11. The car now wants to die the last 3 MPH of coming to a stop instead of the last 6 MPH, but now it runs rough at idle instead of the “running on fumes, going to die” condition it had in #4, above. Same when accelerating, it acts like it wants to die until it is at 5 MPH or so then switches to just being rough (before, this “change” occurred at 10 MPH). If I just give it some gas it responds right away even if it is at 1 MPH. It seems like the engine has the same “rhythm” as it had before the fuel pump replacement, even though it is not threatening to die now when stopped in drive or reverse. I do not know what a misfire is for certain, but if you told me it causes the engine to skip a beat every time it hit that cylinder, I would say yes sir, that seems to be occurring. If you turn the AC on/off it now has no impact at all, as well.
12. I uploaded audio to YouTube of how the engine sounds (near the end of the audio I give it some gas): https://www.youtube.com/watch?v=qPwhqJgNCXI&feature=youtu.be You may be able to pick out an “exhaust-leak-like” clicky sound. Listening with my stethoscope’s cone attachment, the exhaust-leak sound occurs along the length of the exhaust pipe. If I use the metal rod attachment I can also hear it occurring along the length of the exhaust pipe. This was not present before the work in #2, above, and it does not occur on the right side of the engine. Maybe this is a problem because the right side doesn’t have it or maybe this is a problem because the left side does, not sure.
13. I no longer seem to smell exhaust, but maybe this is because I have not done any city driving yet.

I think that is all…any advice or thoughts would be greatly appreciated. It seems overwhelming to me – but if I do not discover a problem with the work done in #2 above I am leaning toward EGR valve. If this is stuck open or in some other way malfunctioning, from what I understand it would explain the extra engine heat (despite the temperature gauge reading normal) and the poor performance at higher speeds / when hot in addition to explaining the fuel economy issue. It could also explain the exhaust smell every so often…

Other test items on my list aside from EGR:

• Drive with the pressure gauge on…see if it loses pressure when accelerating under load.
• Visually check (again) for any spark arcing.
• Test EGR valve. I am not sure what type it is, but I have tests for all three types and identification information once I read the part number on it. It is quick to test this so doing it first.
• Quick test of MAF by unplugging it. If no difference, investigate further.
• In-line spark plug tester, make sure all have strong spark (and I guess different coloring, too?) at different RPMs
• Remove boot from each plug (I’ll be doing this anyways during the in-line test) and see if it impacts engine RPM/sounds differently than the others. I may pick up an IR thermometer as well to see if a cylinder is colder or hotter than others.
• Examine vacuum lines AGAIN, take each one off and feel for suction continuity…lightly zip tie the ones I have looked at to be 100% sure I am keeping track. Disconnect lines entirely and see how it runs. No difference should indicate a big problem somewhere which I am somehow missing.
• Remove all spark plugs, look for fouled ends, cracked ceramic, check any for bad gaps or damaged tips.

Topic

[Joeseph Mama]

clean the fuel injectors.

[Glenn]

Expr1, I hope my reply won’t be overly simplistic to you. One of my vehicles has a GM 3800 engine. One of the common occurrences with a high mileage 3800 is carbon build up in the EGR valve and passages. Sometimes it will get stuck open even intermittently. Mine actually had a small piece of carbon break off, thus preventing it from closing all the way. This will usually quickly generate a DTC such as “PO 401, 402, 403.” Here is my simple suggestion; Take the EGR valve off the car and visually inspect the EGR plunger (on the side that contacts vehicle when bolted on). With a small screwdriver/ tool, make sure the plunger is moving freely in and out. Also, check for the presence of carbon particles. With some brake cleaner, cue tips and a bit of patience, you can clean the EGR plunger (don’t know technical name) until it moves in and out freely. The idea is is to clean it thoroughly enough until it moves in and out with no resistance whatsoever. Generally this will clear up the problem if related to the valve. They do fail, but it’s less common on the GM 3800. Fortunately, it’s easy to access. I’ve done all of the above in less that half an hour. Best of luch and keep us posted.

[Kevin]

Thanks guys! I moved those two to the top of my list. Injectors clear the way for easy access to the EGR, but if I find any issue with the EGR I will test with just the injectors cleaned and do EGR after. That way we can avoid a “Wait, what fixed it?” situation…

One injector (passenger side of engine) seemed to spray in an unreliable pattern, sometimes just two streams. I had to run carb cleaner through it twice before it had a reliable pattern of gas spray…taking a short break now to get the fumes out of my system then back to it!

[Kevin]

Progress! It drives much more smoothly with cleaned injectors (also, all ohm’d out within spec); when the engine was cold for a glorious 3 minutes I had clean power. 🙂 It only does one “I’m about to die” lope when coming to a stop now and most of the time it no longer tries to die or hesitate when taking off.

Roughness is still there and still gets worse as it gets hot but engine is quieter overall (I am using 200 fewer RPMs now to do the same acceleration, so I think that is why it is quieter). I made sure to put the injectors back in the order they were originally so that if they were at fault it would not change the sounds I hear.

Since the sound the engine makes is worse in drive I nosed it to another vehicle, left it in drive and listened. I was able to hear the #7 cylinder making a different sound than the others. It clicks the same at the fuel injector, but with the cone attachment on my stethoscope, that one is just…different near to the spark plug, more echoing and deep, hard to explain. Sticks out like a sore thumb, though.

I plan to move that #7 injector from the rear of the engine to the front and see if the sound follows. If it does not follow, I am going to swap the spark plugs. If it does not follow then, I am going to put the old spark plug wires back on. If that does not resolve I am going to assume that the engine just echoes differently in that cylinder…and maybe move the injector to the right side of engine and see if the exhaust noise follows to that side, just for good measure.

EGR – wow, more like “EGTar” – I had to push that rod hard to get even a bit of movement. If I shake it I hear fine rattling inside and black powder falls out and it is simply coated in black powder internally otherwise. Still focusing on that odd cylinder first but EGR seems in trouble too.

Code 44 came back, lean exhaust on left side. Same side as that odd-sounding cylinder, hmm. Letting engine cool then back at it…

[Kevin]

Switched that injector from the back of the engine to the front – definitely has more power. It is still rough but not rough as often. It still loses power when hot.

The exhaust sound did not relocate itself along with the injector – I am actually going for a power balance test before I examine plugs. Took me a bit but found Eric’s writeup here and going to follow that: http://www.ericthecarguy.com/faq/solving-automotive-performance-issues?start=3

Will cancel each cylinder and look for 1) an RPM loss which does not match the other cylinders and 2) listen for that “exhaust” sound to go away.

[Kevin]

Disconnected each fuel injector twice (once while listening with my ear and once while listening with the stethoscope); all of them caused an RPM drop except for that pesky #7 again. It stayed above 700 RPM where the others caused dipping below 700 RPM. None of the cylinders when cancelled caused that exhaust noise to go away…going to examine plugs and spark next, starting with #7.

[Kevin]

Nearly out of time so I am heading home on the final test drive of my vacation. Plug wire #7 was burnt badly (touching the exhaust) and nearly 1/4″ of it was exposed wire. For verification purposes I put a spark tester on it: good spark but that 1/4″ exposed part would jump to anything it could get near. Put the old wire back on and routed it 3″ away from the exhaust (no one tell GM :whistle: ).

Started it up, “exhaust sound” is still there but unless I am damned mistaken it is now on both sides of the engine and sounds healthy. Will listen more later to verify. No more excessive exhaust noise from the tail pipe…unless I disconnect the pesky #7 cylinder, then the excessive noise begins. The engine RPM is lower at idle and when I remove the #7 fuel injector the idle is now impacted like the other cylinders.

The EGR is obviously still a huge problem but will fight that fight next week unless the car drives very poorly…will report back once the trip home is complete.

Thanks again and hopefully if this does not resolve the issues it at least clears the way to diagnose things further.

[Kevin]

Good news, engine is running very smoothly with nice power – I still note a hint of lack of power at higher speeds but quite acceptable and nowhere near as bad as when #7 cylinder was misfiring. I think we are good!

I am going to repair or replace that EGR within a few weeks: if the EGR fixes the hint of lack of power at higher speeds I will post here again, otherwise just assume it had no impact or maybe fixed other unrelated things.

Once again, thank you both! 🙂 I will watch and see if I can contribute back to the forum. There is bound to be some low-hanging fruit I know enough about to help others with.

[EricTheCarGuy]

Just some insights. EGR is only active under load, or it should only be active under load. It can only effect the idle if it’s stuck open.

Reading your post I kept wondering if you had checked for vacuum leaks. I know you said you had an issue with a vacuum line, but I don’t know if I remember if you checked the intake manifold in particular.

Also, just for the heck of it I’m going to suggest you check for an exhaust restriction.

It can effect performance, particularly when hot.

More information on solving performance issues here.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

Good luck and keep us posted.

[Author]

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