Stuttering engine please help (Page 1/3)
tbone42 JUN 13, 05:57 PM
86 Fiero 2.5

I've been having a stutter when I step on the gas. It used to take off at start, too, but it was the TPS and I replaced that . That's fixed. Stutter is getting kinda bad. I've had a little bit of a knocking noise very recently, so I'm thinking they are the same thing. I've replaced a ton of stuff this week: EGR, TPS, new K&N filter, plugs, coil, wires, fuel filter. I have spark and fuel delivery, although I don't have a fuel pressure gauge it is cone spraying and looks right.

I thought it might be the timing. I had trouble getting it timed because the mark is kinda wandering, so it's best guess that it's at 8btdc. (Yes I jumpered the aldl) I also did the timing chain test and it was only 2-4 degrees before the distributor rotor started moving, so I am fairly confident this isn't a loose timing chain. Distributor was new about 8k-10k miles ago, but I pulled the ICM and repasted it with thermal goo. I really don't see the distributor as the problem...but I will replace it if nothing else works.

I just did a compression test because frankly, there's not much else I think I can do. The numbers were not what I was expecting:
128, 150, 160(ish) 170(ish)...I get less marks on my tester higher on the scale. It was a dry test (I think) i don't know how to do it any other way than with the tester I have, and don't have a lot of tools for this.

So what do those high numbers on #3 and #4 possibly mean? Could it be related to what I'm experiencing? Also, the wondering of the timing mark at +2-4 and -2-4 ...is that maybe because of the high compression in #3 and #4?

My brain is telling me it could also maybe be blocked exhaust flow, but not sure. I am getting a chuff chuff noise and a *little* water coming out the exhaust. Figured I'd ask and see what you guys have for me with the info provided.

Thanks for any info, I really appreciate you guys.

[This message has been edited by tbone42 (edited 06-13-2023).]

82-T/A [At Work] JUN 13, 06:05 PM

quote
Originally posted by tbone42:

86 Fiero 2.5

I've been having a stutter when I step on the gas. It used to take off at start, too, but it was the TPS and I replaced that . That's fixed. Stutter is getting kinda bad. I've had a little bit of a knocking noise very recently, so I'm thinking they are the same thing. I've replaced a ton of stuff this week: EGR, TPS, new K&N filter, plugs, coil, wires, fuel filter. I have spark and fuel delivery, although I don't have a fuel pressure gauge it is cone spraying and looks right.

I thought it might be the timing. I had trouble getting it timed because the mark is kinda wandering, so it's best guess that it's at 8btdc. (Yes I jumpered the aldl) I also did the timing chain test and it was only 2-4 degrees before the distributor rotor started moving, so I am fairly confident this isn't a loose timing chain. Distributor was new about 8k-10k miles ago, but I pulled the ICM and repasted it with thermal goo. I really don't see the distributor as the problem...but I will replace it if nothing else works.

I just did a compression test because frankly, there's not much else I think I can do. The numbers were not what I was expecting:
128, 150, 160(ish) 170(ish)...I get less marks on my tester higher on the scale. It was a dry test (I think) i don't know how to do it any other way than with the tester I have, and don't have a lot of tools for this.

So what do those high numbers on #3 and #4 possibly mean? Could it be related to what I'm experiencing? Also, the wondering of the timing mark at +2-4 and -2-4 ...is that maybe because of the high compression in #3 and #4?

My brain is telling me it could also maybe be blocked exhaust flow, but not sure. I am getting a chuff chuff noise and a *little* water coming out the exhaust. Figured I'd ask and see what you guys have for me with the info provided.

Thanks for any info, I really appreciate you guys.




Can you do something for me? Disconnect the MAP and see how it drives. Let me know if it changes. Just a thought. When I had really bad chugging... almost like a bucking, I disconnected my MAP (which I guess goes into limp mode) and the car drove much better. I then later replaced the MAP sensor and that solved the problem.
Patrick JUN 13, 06:14 PM

quote
Originally posted by tbone42:

I just did a compression test...128, 150, 160(ish) 170(ish)... So what do those high numbers on #3 and #4 possibly mean? Could it be related to what I'm experiencing? Also, the wondering of the timing mark at +2-4 and -2-4 ...is that maybe because of the high compression in #3 and #4?



I'd be more concerned about why #1 is so much lower than the rest.
tbone42 JUN 13, 06:40 PM

quote
Originally posted by 82-T/A [At Work]:


Can you do something for me? Disconnect the MAP and see how it drives. Let me know if it changes. Just a thought. When I had really bad chugging... almost like a bucking, I disconnected my MAP (which I guess goes into limp mode) and the car drove much better. I then later replaced the MAP sensor and that solved the problem.



Will do. It just started pouring rain and I have a few things taken apart so I gotta wait for the rain to stop, put it back together and I'll give it a go. Thanks Todd I'll let you know.

Patrick- I'm going to retest all when the rain stops, that was the first cylinder I did maybe I didn't have the tester all the way seated in the plug hole. I just rain out of time, the sky is crying.
Patrick JUN 13, 07:07 PM

quote
Originally posted by tbone42:

Patrick- I'm going to retest all when the rain stops, that was the first cylinder I did maybe I didn't have the tester all the way seated in the plug hole.



Also remember to have the throttle wide open for each test.
tbone42 JUN 13, 07:14 PM

quote
Originally posted by Patrick:

Also remember to have the throttle wide open for each test.



🤦‍♂️ Yep, forgot that and I knew it too. Thanks Patrick.

Also going to mention I have no codes because I forgot to earlier. I cleared them earlier in the week when I did the EGR and the TPS and none have come back with plenty of driving. Now...If I remember correctly it was 34 and 45. And code 34 is a MAP code I think sooo..Todd may be onto something. We'll see when the rain ends.

[This message has been edited by tbone42 (edited 06-13-2023).]

tbone42 JUN 13, 08:32 PM

quote
Originally posted by 82-T/A [At Work]:


Can you do something for me? Disconnect the MAP and see how it drives. Let me know if it changes. Just a thought. When I had really bad chugging... almost like a bucking, I disconnected my MAP (which I guess goes into limp mode) and the car drove much better. I then later replaced the MAP sensor and that solved the problem.



Alright I got a brief period of light sprinkles and put everything back together except the MAP. Left the electrical unplugged. It wouldn't even stay running with it unplugged. So maybe it needs a new one because it is functioning marginally, but it definitely is worse unplugged.

In fact, after the compression test and MAO check, it feels like it's stuttering even worse. FML I need this car for work Thurs thru Tues, I gotta take some of the chop out of how it's running tomorrow or I'm screwed.

I'm looking at a caddy I want to buy on next Tuesday, but dang it I need this car to run until then. Shoot.

Could a PCV failure cause this stuttering? I'm just guessing now I think.

[This message has been edited by tbone42 (edited 06-13-2023).]

tbone42 JUN 13, 08:42 PM
Ok, also just wondering if maybe my distributor is not in there right. I'm looking at the rotor, which end faces the #1 post? The side with metal tab or the side with the bump? If it's the bump I think it's cool, if it's the metal prong it might be in there wrong. This is a pic of distributor with my engine (supposedly) at 8 btdc according to the mark:
Patrick JUN 13, 08:49 PM
This is starting to remind me of an issue I had with my '84 years ago...

Tried three different MAP sensors, but 2.5 engine still bogs badly when accelerated

Turned out it was low fuel pressure.


quote
Originally posted by Patrick Here:

I disconnected the fuel filter (it was very clean inside) and connected a fuel pressure gauge onto the end of the fuel supply line. I then jumped terminal "G" at the ALDL connector with 12v from the cigarette lighter to run the fuel pump. The gauge showed a grand total of 4 lbs pressure while the pump was running, and immediately dropped to zero when the power was cut.

I suspect that short chunk of flexible hose inside the tank has rotted.


[This message has been edited by Patrick (edited 06-13-2023).]

tbone42 JUN 13, 09:08 PM
Yeah, I'll have to see if there's a cheap tester I can buy, money is just an issue the next two weeks because of me buying that other car.

I hate changing the fuel pump in these things, would be nice to not have to again...but I also just want it fixed whatever it is so I'll do what I must.

I adjusted the timing just a little more to a higher btdc, maybe 2 degrees, and it's running better again. I still can't jump on the gas in 2nd and 4th or it stutters, but If I accelerate slow and smooth I get little to no symptoms.