91 GS - "acceleration bounce"

ASSISTANCE Stock Engine-Bay Components
1

Hello. I have a 91 GS with a lot of work done. Basically this car sat for about 5 years in a barn and I thought it would be great to bring it back to life. The car started as an automatic, but I have swapped it over to manual (used) transmission, while I also rebuilt the engine (seals, bearings, rings, valves, etc). I am still using the automatic ECU, as I have found no real reason not to locate another one, other than a CEL for a removed EGR system (using a block off plate on the manifold).

I’ve had some idle issues for a while that I have almost completely solved. Basically the former owner messed with the throttle stop to fix other issues, and i’ve had some difficulty getting that and the TPS back where it should be.

On to the problem now:
Since I have slowly fixed some of the other issues, the most glaring problem is a problem that occurs under mild acceleration, between 1,500 and 2,000 rpms, regardless of gear, although it is more apparent with lower gears.

Best I can describe the feeling is a “bounce” or stumbling acceleration. If am going up a small incline and I try to hold steady in 2nd and about 1,600 RPMs, i can really feel the issue. Maybe 4 “bounces” a second? I can push through the and once I get past about 2,000-2,200 rpms, I don’t notice it anymore.

I honestly can’t tell if this is a misfire or something else.

I’ve replaced the spark plugs (2nd set after rebuilding the engine), checked for vacuum leaks, swapped TPS, checked the valve timing and ignition timing (many times), checked the fuel pressure, I have a new IACV… and more. Nothing seems to have affected this issue. Issue occurs regardless of engine operating temp, although it does seem less noticeable after driving at 60+ mph for a few minutes.

There is one other issue that may or may not be related, and that is at idle, the idle speed will fluctuate slightly, but it seems more like something is cutting off the fuel or air completely for one or more cylinders, which causes a momentary drop of about ~100 rpms (according to the tachometer). I really only notice this at normal operating temp. I have the FITV closed up as far as it will allow, but seems

I can post a video if anyone thinks it might help.

Edit: I have hooked up a vacuum gauge at idle, and it shows a rapid “flick” or bounce between 20 and 21 in.Hg. Normal decrease and increase on throttle change.

2

can you locate a known good distributor for test?

3

Unfortunately not. I did actually replace the distributor with a rebuilt one (local autozone I think) shortly after rebuilding the engine, partly because of the idle speed drop and because the original was pretty corroded. All new ICM, Coil, cap, and rotor was included

I could put back the original, but I’m pretty sure it had the same acceleration issue.

4

May as well give it a shot

5

Thanks. I’ll give that a go.

Side question, is it normal to read about .02 volts between the TPS ground and the (-) battery terminal, with the key ON?

6

i’d say a 20mv drop across the ground is acceptable. definitely not going to cause an issue

7

Haven’t had time to swap the distributor just yet, but i’ve been paying more attention to other things the car does, and wondered if this might be related:

When decelerating in gear and clutch out, the car will sort of jerk, once it climbs down to about 1,500 rpms. Its almost like I’ve just lightly tapped the gas.

8

I swapped back to the old distributor and the same issue persists.

I did go ahead and replace the fuel filter again, just in case the other new one collected some left over crap in the lines from sitting so long. I also swapped in a manual ECU (think from a 92) and neither has affected the “bounce” in the 1,500 to 2,000 rpm range, or the possible misfire around idle.

I’ve also rechecked the valve lash, and brought it back to a more conservative setting (.006 intake and .007 Exhaust). No change.

I’ve done a cylinder leak test (cold), and was around 12 - 15% leakage.

Compression test (warm) showed a range of 140 to 149 psi across, with little to no change when adding oil. - Seems a bit low, but could also be a crappy gauge.

Fuel pressure is within spec, but on the low side.

I don’t think its mechanical, but i’m willing to give just about any theory a shot.

9

I had just taken out the engine harness to give it some tlc and after getting it back in 2 weeks later sam thing happened to me. I had to drive the car easy just to make it run smooth.
So I checked everything with the engine running started to move the harness around the distributor and boom.
It would miss or stumble soon as I touched the distributor plugs. I’m thinking I ripped the inner wires.
After a closer look I notice the ground wire on the rear water neck was moving with the bolt in place after I hand tighten it 2 weeks ago.
It was the ground wire that came loose. Issue went away after that.

10

yes. check your ground cluster at the tstat housing. make sure it’s clean and tight.
and does this problem happen every time when the conditions are met? or is it intermittent?

11

I’ve had this issue in the past and replacing the igniter module inside the distributor has solved it every time. The weird thing is that it doesn’t matter between the distributors in your case. They’re fairly cheap at NAPA so it might be worth a shot.

12

Thanks guys.

I checked the ground at the t-stat housing. It was secure and relatively clean. I also checked the main ground at the transmission, which was in good shape. Finally, I checked the ground to the valve cover, and realized I had it connected to the rhd accelerator mount, which I then corrected by connecting it to the nearest actual valve cover nut/bolt. I actually built a new ground cable out of 10ga wire, since the original broke and the previous (temp) one was just 14ga. - I could have sworn that this made a difference at first, but after driving all day, it didn’t help.

I also inspected every connection I could find in the engine bay, including the distributor connections, for loose wires, and even jiggled them with the engine at idle speed. Couldn’t notice any sudden misfires or corrections in relation to those tests.

The problem I believe to (now) be somewhat intermittent. There is always sort of a lack of power in that RPM range and always the slight drops in rpms/misfires around idle, but sometimes the issue is just way worse than others while driving. The bounce feeling I get (whole car shaking) does seem to be more prevalent when the car is fully warmed up and driving up a slight incline.

When searching for how to reset the ECU, I came across a team-integra posting that referenced a G2IC post, that explained a common similar issue with the igniter causing the tach to jump and a code 15. I’m not getting the code 15, and don’t notice tach bounce when driving. I think I will try to strengthen the connections on the igniter and maybe replace if that doesn’t help.

boltonhonda, did you mean that this issue occurs between different distributor models, or that the part (igniter) is universal?

Thanks again.

13

go after fuel pressure. let’s take that out of the equation at least. you say it’s within spec, but are you testing while the problem occurs? because it’s very difficult to confirm a problem without it occuring. install your pressure gauge in a spot that’s easily visible while driving. i like to zip tie it to the windshield wiper, or run it into the cabin. watch what the pressure is doing while the problem occurs. if it doesn’t seem to be effected, move onto ignition. when ignition testing use an HEI tester. this simulates load on the ignition system. testing spark in open atmosphere is completely different from what’s going on under cylinder pressure. the HEI tester is cheap, and easy to use. pull your spark plugs out and examine them. if you read them, they can tell you a whole lot of information.
another test you can do with regards to fuel is, with the gauge installed, observe base pressure at idle. now, pinch the vac line leading to the fpr. pressure should increase by approximately 10psi. if it doesn’t, suspect the fpr is at fault. still good? now, with vac line pinched, snap the throttle 3 times. pressure should not decrease by more than 5psi during snap throttle. if it does, suspect a weak pump.
in summary:
scrutinize fuel pressure. perform the fpr and snap throttle tests first. then, drive the vehicle with the gauge in sight and observe. if that goes fine (after simulating the problem), inspect your plugs. see how they differ from eachother. check for signs of certain issues. read them. then, if still nothing, HEI test. if none of this finds the issue or at least gives you a scent to sniff, then we need to move beyond the general testing and over to more specific, advanced testing

14

try this first actually, since it’s quick and easy to do, disconnect the o2 sensor and see if the problem persists

15

Problem persists with O2 sensor disconnected.

I have not tested the fuel pressure with the car in motion. Seemed risky, but I like your idea of using the wiper blade :slight_smile: - I’ll give that a try once the car cools off.

i’m not sure I know what to look for in purchasing an HEI tester. Most I see just connect a plug to the plug wire and the ground. How does it simulate load? - I have connected an in-line tester, but that didn’t tell me much, other than the light blinking normally.

I’ve checked the plugs several times, but to my eyes, they look pretty normal. If anything, they would be on a lean side, as opposed to running rich, but they look normal to me. All 4 are the same in appearance.

I had tried pinching the fpr vacuum before. Actually had to pinch and completely disconnect it from the fpr to get the fuel pressure to change. It rose about 10 psi. I did not try snapping the throttle cable, but I will add that to the list.

Edit: Never mind the HEI tester. I believe I know what I need to get.

16

checked fuel pressure with the issue, and it appears in the normal range. If I press hard on the gas, I feel the hesitation more (less bounce) and the fuel pressure goes up (from 28 to 35 psi). While at idle and the FPR disconnected, I see a rise of almost exactly 10 psi (from 28 to 38 psi). Snapping the throttle showed no decrease in pressure (least not shown on the gauge).

Tested with HEI - Getting consistent spark on each plug. I changed the Igniter and the Coil anyway… no go.

Ok. I’m starting to suspect that I may actually have a slightly leaking head gasket. Does that sound like it could remotely be the cause? My suspicion is due to this: Low-ish compression numbers for a rebuild and a very slow disappearance of coolant from the reservoir.

I didn’t mention the coolant disappearing because I figured I had a slow leak from a hose or the radiator drain plug (actually caught that leaking in the past). I go from Max to Min in the reservoir over about 700 miles, I would estimate.

After I considered this as possibility, I drove the car for about 5 miles, stopped and checked the tail pipe. No visible steam coming out, but I could feel hot moist air quickly condensing on my hand. :frowning: - Its about 80 degrees F and I think 70% humidity outside, if that matters.

Thoughts?

17

a mechanical issue is not going to be intermittent. it’s gonna do it, under load, or whatever the criteria to cause it, every time. can you get it to do it every time under the same conditions?

18

Today, yes it seemed to always occur under the same circumstance… tomorrow, no idea.

I’ve finally been able to do a leak down test at normal operating temp. It is, by no means, a very accurate guage, but im showing about 18 to 20 percent leakage. Only signs of leakage at 15 psi is through the rings.

Ignoring the “bounce” while driving issue for a moment. What would an intermittent misfire sound like from the exhaust? A muffled popping sound?

19

a misfire is felt more than it is heard. if a cylinder were misfiring though, you’d have seen some sign of it on at least one of the plugs. kinda stange that they all looked even steven. could mean that the issue isn’t segregated to one or two solitary cylinders. i think you need to start checking your inputs.
ECT
MAP
TPS
IAT
however, to check TPS properly, you should use at least a graphing meter. all you’ll be able to do with a dvom is check it’s range really. but the others you can check

20

The plugs look pretty normal to me, at least:
http://imgur.com/5bFI4CL

This one looks a little different, with a little more “ash”(?) on the plug
http://imgur.com/MaKd7N0

I don’t think I’ll get access to a graphing meter any time soon :slight_smile: . I’ve messed around with the TPS, setting it at a lot of different closed throttle settings, including .44v, to as high as .52v. Once I set it upwards of .50v, I tend to get a CEL code relating to fuel mixture (actually don’t recall the exact code). I’m currently at .48v closed throttle, according to my multi meter. What should the TPS be set at? I’ve seen so many conflicting suggestions of .50v, .48v and .45v. The .45v actually came from the hondata website.

Also, just in the interest of full disclosure I have swapped over to manual ECU (the original was an Auto ECU). This manual ECU is getting a barometric pressure CEL code (13). The old auto ECU was getting a code 12 (EGR). I am still running the auto intake manifold with a block off plate for the EGR. And of course, the issue exists on both ECUs. - Just in case that wasn’t made clear before.