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91 DPFI sputtering issue.

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Old 10-14-2017, 10:30 PM   #1
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Default 91 DPFI sputtering issue.

So, Iím having this huge sputtering issue that for a while would only happen on the to work, not the drive home. Drive home the car would run absolutely fine.

Things Iíve done:
New (re-man) alternator (bench tested as good)
New fuel filter
New plugs and wires
New Dizzy
New 02 sensor
Cleaned the IACV
Ran sea foam through the system
and hereís the real kicker:
swapped in a completely rebuilt motor, and itís still doing this.
Timing seems good. It does idle a tiny bit high. Also it did this before running at full advance and at somewhere in the middle. Mechanical timing is perfect.

I do get a temporary battery light on startup (not the normal key on engine off one) that goes away with a rev.

Basically, the car will rev to about 2000rpm and then start sputtering or worse itíll not really fire at all until I floor it, and then itíll buck.

I have video of it doing it super bad today.
What else am I looking at?
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Old 10-15-2017, 05:58 AM   #2
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Default Re: 91 DPFI sputtering issue.

You know, mine has been doing this for a while too (90 DPFI). I haven't done as much as you but I have also replaced alternator, distributor, plugs, wires, and sea foamed. I may try a new fuel filter and see if that helps. Anyhow, my issue is mostly during idle while the car is warming up. The idle will start dipping and it will start sputtering, sometimes bad enough to stop running. I initially thought this was an ignition issue, because the tachometer drops pretty hard when it is sputtering. I think in reality I was having a non-related ignition issue, because I was having the tachometer needle drop to zero then back up (very quickly) while driving normally. I was using a then 7-year-old "Distributor King" distributor, and replaced it with a cheap Rock Auto one...I'm very disappointed with the Rock Auto one and won't buy one from them again...but that's another topic.

The sputtering issue is usually more of an issue for me in the winter when I want to let my car warm up for about 20 minutes before I get in to drive it. Even though you've done new plugs, have you pulled them to look at them recently? I put new plugs (and wires) in the car Sept. 2016, and then pulled the plugs because of the issue August 2017, less than 1 year later. The ring that the electrode is attached to (that faces the combustion chamber) was heavily pitted on (I think) 3 of the 4 plugs, and they looked rusted and ancient on this ring. They were also difficult to remove...I was worried about one breaking or damaging the threads in the head, but all seemed fine when visually inspecting the threads and putting the new plugs in. I pulled the plugs again about 1 month later, and the Number 2 plug was already starting to look pitted/rusted. Just curious if you are seeing something similar with your plugs.

I wonder if you and I are having an issue caused by dirty injectors? It may be worthwhile to pull both DPFI injectors out of the throttle body and clean them thoroughly. I've got some of the parts to do an MPFI swap, and hope to be able to get the remaining pieces and do the swap in the next few months. Hopefully that will ultimately solve the issue.
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Old 10-15-2017, 03:09 PM   #3
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Default Re: 91 DPFI sputtering issue.








So, hereís some photos of what the injectors and the plugs look like: anyone see anything of concern? Also what are the colored caps on the back of the injectors and does it matter that the one on the green injector is broken?
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Old 10-16-2017, 09:38 AM   #4
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Default Re: 91 DPFI sputtering issue.

Have you checked all the vacuum lines? A bad line on the MAP sensor will make the car run like crap. Could also explain the high idle. Have you also checked and/or adjusted the throttle position sensor (TPS)? I've had to replace mine twice. Vacuum hose is cheap and the TPS can be checked with a multimeter.
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Old 10-16-2017, 09:45 AM   #5
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Default Re: 91 DPFI sputtering issue.

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Have you checked all the vacuum lines? A bad line on the MAP sensor will make the car run like crap. Could also explain the high idle. Have you also checked and/or adjusted the throttle position sensor (TPS)? I've had to replace mine twice. Vacuum hose is cheap and the TPS can be checked with a multimeter.
vacuum lines are all good. I forgot to mention, no CEL either. When I accidentally unplugged the line going to the MAP sensor I got an instant CEL.

I heard the TPS is super hard to adjust and itís far better to just get a throttle body.

I should also mention, since pulling the plugs and fuel injectors and looking at them and plugging them back in? The car ran great.

Iím gonna have to see if It does the issue again this morning. I borrowed the fuel pressure tester from work to see how the fuel pump is doing.

Its just baffling me how itís intermittent. Drive to work: bad, drive home? Great.
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Old 10-16-2017, 11:07 AM   #6
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Default Re: 91 DPFI sputtering issue.

It's honestly not that hard. I looked into the Honda throttle body replacement and it was like 300 bucks. Almost all Hondas around this vintage have the same sensor. The hardest part is hacksawing the original screws off. It's mounted with two screws with riveted heads. My first TPS was bad, and the second went out of adjustment by itself. I solved some slight bucking issues by adjusting it again. Even .05V out of spec makes the car a little pissy.

You can probably score the sensor from a yard for less than 10 bucks, and Lowes carries the replacement allen-head screws. I recommend at least measuring the voltage instead of throwing parts at it.

You mentioned you still get a battery light at startup.. Have you checked and cleaned all the grounds in the engine bay? I do this every other year and always notice a difference.

The fuel pressure tester is a good step. It needs a special banjo bolt adapter to work on these cars though. I still need to measure mine. I've been getting 20mpg city with my 90 Si for around 4 years now
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Old 10-16-2017, 02:37 PM   #7
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Default Re: 91 DPFI sputtering issue.

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It's honestly not that hard. I looked into the Honda throttle body replacement and it was like 300 bucks. Almost all Hondas around this vintage have the same sensor. The hardest part is hacksawing the original screws off. It's mounted with two screws with riveted heads. My first TPS was bad, and the second went out of adjustment by itself. I solved some slight bucking issues by adjusting it again. Even .05V out of spec makes the car a little pissy.

You can probably score the sensor from a yard for less than 10 bucks, and Lowes carries the replacement allen-head screws. I recommend at least measuring the voltage instead of throwing parts at it.

You mentioned you still get a battery light at startup.. Have you checked and cleaned all the grounds in the engine bay? I do this every other year and always notice a difference.

The fuel pressure tester is a good step. It needs a special banjo bolt adapter to work on these cars though. I still need to measure mine. I've been getting 20mpg city with my 90 Si for around 4 years now
the auto parts store where I work has the special banjo bolt adapter with the fuel pressure tester! (Irish name, green shirts, if youíre wondering). Itís a rental tool.

I was at pick n pull today and scored a PM5 Auto ecu (I have a CEL, but itís just for my nonexistent neutral interlock switch as my car is stick). Car seems to run way way way better, although itís not hunting idle. Iíll do an idle relearn and see if it stops. Do I have to back probe the TPS to test it?
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Old 10-16-2017, 02:54 PM   #8
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Default Re: 91 DPFI sputtering issue.

Not gonna lie, I just trimmed back the insulation ever so slightly. I know this wasn't the best way to go about it, but I found that back probing never worked. You can also do a resistance test directly on the sensor with it unplugged. I forget the exact range but I'm at work so I don't have access to my shop manual right now.

I seriously need this banjo bolt tool. Can you get me a part number? I would rather buy one since I'll probably always own one of these cars.
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Old 10-16-2017, 03:43 PM   #9
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Default Re: 91 DPFI sputtering issue.

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Not gonna lie, I just trimmed back the insulation ever so slightly. I know this wasn't the best way to go about it, but I found that back probing never worked. You can also do a resistance test directly on the sensor with it unplugged. I forget the exact range but I'm at work so I don't have access to my shop manual right now.

I seriously need this banjo bolt tool. Can you get me a part number? I would rather buy one since I'll probably always own one of these cars.
67091 is our part number for it. Itís a rental tool, but you can just keep it. We charge up front for it. Here in Washington youíd be looking at $136.51 with tax out the door. It has the banjo bolt fitting in it.
So this is where we were at idling. Looked to be at about 25 just cycling the key on and off. Fuel pump bad?
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Old 10-16-2017, 04:12 PM   #10
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Default Re: 91 DPFI sputtering issue.

I should also add, I drove it to the store and back on lunch and so far it hasnít sputtered (this is on the PM5 ecu) but it is still hunting the idle. Gonna do an idle relearn tonight and see if it settles down.
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Old 10-17-2017, 10:55 AM   #11
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Default Re: 91 DPFI sputtering issue.

I'm not 100% sure what a DPFI is supposed to be at, thought I saw 35-41 but haven't confirmed. I believe to test the static pressure you must disconnect the vacuum line to the FPR. I do know all stock b-series fuel pressure regulators I have had would sit at 40 lbs at idle/ should hold that pressure after the engines off. It will go up and down if you play with the gas while the engine is on of course.
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Old 10-17-2017, 01:19 PM   #12
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Default Re: 91 DPFI sputtering issue.

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I'm not 100% sure what a DPFI is supposed to be at, thought I saw 35-41 but haven't confirmed. I believe to test the static pressure you must disconnect the vacuum line to the FPR. I do know all stock b-series fuel pressure regulators I have had would sit at 40 lbs at idle/ should hold that pressure after the engines off. It will go up and down if you play with the gas while the engine is on of course.
Hmmmm. I think I read that too. Seems like my fuel pump isnít putting out enough pressure then.

Also currently Iím sitting here hoping the car learns how to idle instead of doing what itís doing.
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Old 10-17-2017, 01:56 PM   #13
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Default Re: 91 DPFI sputtering issue.

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Hmmmm. I think I read that too. Seems like my fuel pump isnít putting out enough pressure then.

Also currently Iím sitting here hoping the car learns how to idle instead of doing what itís doing.
Are you checking fuel pressure before or after the filter?
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Old 10-17-2017, 05:26 PM   #14
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Default Re: 91 DPFI sputtering issue.

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Are you checking fuel pressure before or after the filter?
after the filter. Well, on the out line of the filter. Should I have checked it on the IN line?
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Old 10-17-2017, 06:30 PM   #15
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Default Re: 91 DPFI sputtering issue.

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after the filter. Well, on the out line of the filter. Should I have checked it on the IN line?
Nope, and I'm sorry, I missed the fact that you've replaced the fuel filter in the original post. I was wondering if the filter could be clogged, but doubtful on a new filter.
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Old 10-17-2017, 11:46 PM   #16
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Default Re: 91 DPFI sputtering issue.

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Nope, and I'm sorry, I missed the fact that you've replaced the fuel filter in the original post. I was wondering if the filter could be clogged, but doubtful on a new filter.
fun fact, one of my coworkers told me to try blowing through the old fuel filter for sh*ts and giggles, just see how clogged it was. I did so and blew out the clog and a bunch of gas straight into my eyeball.

Last time I ever try that one.

Also today I sprayed a bunch of throttle body cleaner in the throttle body and cleaned out the IACV again. Also did an idle reset a couple times as I had surging idle issues or If not surging, just high idle.

Then I cleaned the throttle body and the IACV and now it idles at just about 1000.

we still have a tiny sputter occasionally, but nowhere near as bad as it was.

Maybe the PM5 is compensating for the lower fuel pressure with slightly more aggressive fuel maps?

either way I think next Iím gonna replace the fuel pump. I can get a new one at work for $30.
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Old 10-18-2017, 07:59 AM   #17
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Default Re: 91 DPFI sputtering issue.

Back when I had my 91 auto DX I had a runaway idle situation just randomly with rough running. It turns out one of the throttle body dashpots had failed internally somehow and my dad just blocked it off and made a huge vacuum leak. This was before I knew anything about cars so I can't get you any more detail than that. I just remember calling him scared shitless because I almost drove through a wall when it first happened lol.

When you do the fuel pump, I really recommend replacing the sock filter and the high pressure fuel hose inside the tank. The sock gets old and may fall off by itself. Also, if you don't replace the little clip they can fall off, then you can't use more than half the tank without stalling as found in this thread: https://honda-tech.com/forums/honda-...rched-3024291/ I also had the return hose leak coming from outside of the tank and it would drip gas on the ground whenever I primed my pump. Don't be tempted to get a sock for anything other than an 88 CRX DX, and be especially wary of a pump/filter combo. They literally manufactured the wrong part for every other year and it's all detailed in that thread I linked.

I forgot to ask.. Does it do this randomly or only when it's hot or cold? Would it be possible to read the fuel pressure on the way to/from and check once or twice during the drive? I also had an ignitor go bad two years ago and it would drop a cylinder or two then stop working entirely after the car warmed up. Have you done resistance checks yet on the distributor parts? I know you said it's new but I've gotten bad crap off the shelf before at auto stores (ESPECIALLY ALTERNATORS )
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Old 10-18-2017, 08:20 AM   #18
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Default Re: 91 DPFI sputtering issue.

Also, what is the weather like where you live? That may help us narrow something down. A bad coolant temperature sensor is another possibility to throw out there, but that would be more pronounced for a hot/cold engine and not time of day. Does the car sit in the sun all day at work? Is it garage kept at home? A bad/going bad main relay can cause weird symptoms but usually results in the car not starting after being in the hot sun all day.

What's going on with this valve cover breather
? And have you checked the PCV system? I know you mentioned you checked vacuum hoses, but I had to get new o-rings for the PCV box where it mounts on the back of the block, and had to replace each of the hoses going up to the intake for the PCV valve on my Si. Edit: I also replaced the PCV grommet because it disintegrated...
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Old 10-18-2017, 02:53 PM   #19
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Default Re: 91 DPFI sputtering issue.

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Also, what is the weather like where you live? That may help us narrow something down. A bad coolant temperature sensor is another possibility to throw out there, but that would be more pronounced for a hot/cold engine and not time of day. Does the car sit in the sun all day at work? Is it garage kept at home? A bad/going bad main relay can cause weird symptoms but usually results in the car not starting after being in the hot sun all day.

What's going on with this valve cover breather
? And have you checked the PCV system? I know you mentioned you checked vacuum hoses, but I had to get new o-rings for the PCV box where it mounts on the back of the block, and had to replace each of the hoses going up to the intake for the PCV valve on my Si. Edit: I also replaced the PCV grommet because it disintegrated...
I live in Washington, so rainy/cold ish. It seemed to happen more when it was sunny out? Also itís been doing weird things on the PM5. Itís idling high again after last night when I cleaned the IACV and it idled nicely. It also did the bouncing idle again slightly today. Hereís the weird thing also, I drove around doing errands today, it didnít do it til right around 12:50 which is around when I go to work every day. That was on the way to the grocery store. On the way back from the grocery store? Nothing. It ran decently.

Alternator is good. I had it bench tested after the first one I got from work was super bad. (It put out 11 volts).
When it was doing the bouncing idle thing yesterday I unplugged the IACV and it ran better. Could be an IACV going bad?

Iím so lost. Also thereís nothing on that breather because I donít have an intake at all. I just have a cone filter ON the DPFI box. The stock intake was long gone when I got the car.
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Old 10-18-2017, 03:03 PM   #20
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Default Re: 91 DPFI sputtering issue.

Also the PCV valve is new. The box was kinda gross, swapped over from the old motor. Seems like everything was fine with that.

OH the car sits outside all day at work and at home.
Some other things: the charcoal canister has been deleted and all the vacuum lines that would have gone to it are plugged.
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Old 10-18-2017, 03:26 PM   #21
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Default Re: 91 DPFI sputtering issue.

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Also thereís nothing on that breather because I donít have an intake at all. I just have a cone filter ON the DPFI box. The stock intake was long gone when I got the car.
Just a heads up, you can get little mini filters for the breather just so dirt and water and whatnot don't get in there. Some think they're a little ricey but I like the look.

JEGS Performance Products 50195: Clamp-On Breather 1-3/8" | JEGS

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Old 10-18-2017, 03:39 PM   #22
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Default Re: 91 DPFI sputtering issue.

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Just a heads up, you can get little mini filters for the breather just so dirt and water and whatnot don't get in there. Some think they're a little ricey but I like the look.

JEGS Performance Products 50195: Clamp-On Breather 1-3/8" JEGS

Iíve been looking at these at work, I should just get one already!
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Old 10-18-2017, 09:10 PM   #23
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Default Re: 91 DPFI sputtering issue.

So, stripped the interior tonight, went to go drive it, battery light stayed on and I had the same idle surge issue and the sputtering was awful to the point of being undriveable. Did notice what seemed to be a ground wire next to the taillight housing that didnít go anywhere.

Also I got a code 14 (as well as 19 but thatís because my PM5 is from an Auto car) Seems like the IACV has given up. Iíve cleaned it twice now.
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Old 10-18-2017, 10:39 PM   #24
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Default Re: 91 DPFI sputtering issue.

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So, stripped the interior tonight, went to go drive it, battery light stayed on and I had the same idle surge issue and the sputtering was awful to the point of being undriveable. Did notice what seemed to be a ground wire next to the taillight housing that didnít go anywhere.

Also I got a code 14 (as well as 19 but thatís because my PM5 is from an Auto car) Seems like the IACV has given up. Iíve cleaned it twice now.

also another update, drove it again, no battery light, one instance of sputtering, still messed up idle and code 14. Got to the store, unplugged the IACV, the car idled pretty low, drove well until I got to my street and it sputtered a bit.

Oh oh and I should say, when I got my car back from my buddies who finished up the motor swap while I was working, on the drive home it sputtered SUPER bad and was a gallon low on coolant. Iíve bled the coolant many many many many times. It does seem to seep a tiny amount of coolant from the hose between the thermostat housing and the block.

What. On earth. Is up with this car.
I should also mention itís raining here.

also my volt meter appears to not be working. Iíll play around with the one at work tomorrow if itís not raining.
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Old 10-19-2017, 12:47 AM   #25
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Default Re: 91 DPFI sputtering issue.




Well hey look at that, that pin on my main relay isnít soldered at all...
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