I need some help. My engine ran like *** at the Expo. If you were in group 4, you probably heard my engine spit and sputter all over the track. I had a major power loss - mostly stock R’s were pulling on me on the straits. Ever since I got home, I’ve been trying to find the problem, but no luck.

From a cold start, the engine idles and runs fine. However, when I first rev over 7000 rpm or so, the engine hesitates. It kind of feels like hitting a rev limiter. The loss of power is very temporary, almost like a hiccup. It will hiccup anywhere from 4-8 times between 7000rpm and 8000rpm. It seems like the more I drive the car and get the engine warm, the problem also occurs in lower rpms and even at idle. When it’s at its worst, the car will stall from idle unless I blip the throttle when I feel it stumbling. It has not thrown a single CEL to give me an idea what’s wrong.

I traced the first occurrence of the problem to a specific 2-day window during which my out of town tuner was installing a vtec lowering modification to my ems (unichip). He tells me that the hiccup first occurred before he installed 290cc prelude injectors on my car, so I’m going to rule out an injector problem for the moment. Tonight, I undid the wiring for the vtec modification that he had installed, but the car still has the problem.

My spark plugs are new and look fine, and my cap, rotor and wires are fairly new. I’ve checked my TPS, and all voltage and resistance measurements are within spec. I have looked for a vacuum leak, but cannot find one. My tuner installed a 2 bar map sensor on my car about a year ago, and I do not know how to test it.

My unichip is a piggyback computer that modifies various signals (e.g., map, tps, timing) before the ecu receives them. I’ve had the unichip on my car for about a year, and I have not experienced a problem with it. Unfortunately, any unichip tuning and diagnostics needs to be done by my tuner, as he has all the software, etc. to run the thing. He’s turned out to be somewhat clueless when it comes to working on Honda’s, so I can’t count on him to diagnose the problem.

Since this problem occurs both on and off throttle, and not necessary under boost, I was hoping someone has experienced a similar problem and can give me some advice on how to diagnose what’s wrong. I am open to any ideas, as I’m about out of them.

 

...well, I'd say probably ignition or fuel. Primary guesses would be either a faulty plug wire, maybe something that dry-rotted or the rotor. (Either bad or screw might be loose.)

Try putting your stock injectors back in, too. Could have a fouled injector. Try running a FI cleaner?

Just some thoughts from a beginner tech.

[edit] compression test yet? if so, #'s? [/edit]

 

The plugs, cap, rotor and wires are all fairly new. The rotor screw is ok.

I cannot reinstall my stock injectors on my own, I'd have to have my tuner change my fuel mapping for the car to run very well with my 240cc's in place. He says he flow-tested the prelude injectors before he installed them, and they flowed between 285-288cc, without any problems.

My first guess is also that it's a fuel problem. The way I can save the engine from stalling at idle by stabbing the throttle makes me think it's fuel related.

 

Do you know for sure which Prelude injectors he put in your car? Cause it sure sounds like a fuel issue to me>
1992-96 Prelude non-vtec Peak and hold 240cc
1992-96 Prelude VTEC Peak and hold 345cc
1997-up Prelude VTEC Saturated 280cc

If by mistake he used a 92 - 96 345cc injector then it is Peak and Hold injector and not a Saturated injector. Which is okay if he used a external resistor pack which would take the voltage from 10 ohms impedance (ITR's saturated injectors use) to 2 ohms impedance.

Hondata's website has some information on this.

edit I just read your latest thread and it appears he used the 280cc injectors... Sorry but maybe he didn't actually flow test them

 

My tuner gave me very specific numbers about flow testing the injectors, so I'm sure they're the right ones. I don't remember the name of the guy that I bought the prelude injectors from, but he seemed very straight-forward about them being the correct injectors. My tuner is also confident that the problem started before he installed the prelude injectors, which makes me think the problem may lie elsewhere.

 

you mentioned a semi-standalone. does it do any type of logging or show any details while running?

just curious if you aren't seeing any CEL's because of the chip... maybe programmed to ignore or not trigger certain CEL's?

 

It doesn't log, but when I'm hooked up to the diagnostic equipment, it shows real-time data. I've thrown other CEL's with this piggyback in place, so I don't think it blocks CEL's.

 

Ok.. well it was just a thought. For example, with my cams and using my obdii ecu.. I'll throw random misfire codes. But when I put in the odbi... don't get'm.

 

What plugs are you running? I have seen GSRs and Rs experience high rpm misfires with Bosch platinums, Splitfires, and Autolite platinums. Just a thought.

 

I've been using NGK bkr7e-11 (copper) for the past 2+ years. I've used 2 sets of new plugs recently to try and rule out a bad plug.

 

O.K., sounds like you ruled out plugs.
How is your fuel? Seen a couple of vehicle with similar symptoms that had contaminated fuel.


Modified by b19coupe at 8:15 AM 4/28/2003

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b19coupe &raquo;</TD></TR><TR><TD CLASS="quote">Seen a couple of vehicle with similar symptoms that had contaminated fuel.
Modified by b19coupe at 8:15 AM 4/28/2003</TD></TR></TABLE>

yeah that happened to me and it gave the exact symptoms batoutahell is discribing, the bad fuel messed up my plugs (even though they didnt look bad). I just swtiched plugs and put 94 in. I also had new ngk plugs that i had been using for a long time with no problems.

I have also seen many similar missfireing and powerloss problems from clogged cats. whats your exhaust setup?

 

I've gone through a couple tanks of 92, 93 and 94 octane with 2 sets of new plugs, and it didn't seem to help. My exhaust is: kami header, 3" carsound cat, 3" thermal. I'll check the cat tonight for obvious clogs, but I'd expect a CEL if the cat wasn't doing its job.

 

A plugged cat won't necessarily cause a CEL. A cat that is hollow or burned out will set a code, and only OBD2 cars have a Cat code; that's what the second O2 sensor is for. The way to test for a plugged exhaust system is to hook up a vacuum guage and rev the motor. If the vacuum steadily drops or is low at steady throttle(about 3500 rpm) , you may have a plugged Cat.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b19coupe &raquo;</TD></TR><TR><TD CLASS="quote">A plugged cat won't necessarily cause a CEL. A cat that is hollow or burned out will set a code, and only OBD2 cars have a Cat code; that's what the second O2 sensor is for. The way to test for a plugged exhaust system is to hook up a vacuum guage and rev the motor. If the vacuum steadily drops or is low at steady throttle(about 3500 rpm) , you may have a plugged Cat.</TD></TR></TABLE>

Very interesting. I have a boost/vac gauge that I can tee into the manifold. Will the test work if I'm reving while parked?

 

Yes. The car does not have to be under a load.

 

Update: I pulled the TPS and bent the prongs a bit to make better contact with the plug. That didn't seem to help.

Next, I hooked up a boost/vac gauge at the manifold and observed what happened at various throttle inputs. At idle and light throttle, vacuum reads about 17" Hg. When I apply steady, moderate throttle, it drops closer to zero. When I apply quick stabs on the throttle, it jumps to zero. Whenever I let go of the throttle, vacuum jumps very quickly back to 17" Hg.

I also observed my fuel pressure gauge. Under light throttle, it stays the same, around 53psi (vacuum hose attached). When I stab the throttle, it jumps a bit into the 60's, but drops immediately when I let go of the throttle.

Do these conditions sound like a clogged cat, a fuel or vacuum problem?

 

I'll add another observation: when at idle, there's a very slight "burp" to the exhaust note. It's not real obvious, but it's noticeable. This "burping" suggests a rich condition, which makes sense, given my sooty spark plugs and exhaust tip, and the tiny specs of carbon on my garage floor behind under the exhaust tip.

When the car was idleing, I did the "wiggle test" on the TPS and MAP sensor wires to see if I could trigger a reaction - no luck. I next went directly to the ecu and shook all of its wires looking for a reaction - none. I did not get around to inspecting the o2 sensor and the cat, that will have to wait until tomorrow night. Does anyone else have an opinion on what might be going wrong?

 

swap out the wires for the stock set or another new set just to try them out. sounds like a occasional missfire under load. they could be arching through the rubber down in the spark plug ***** of the head.

 

Your symptoms do not sound like a plugged exhaust, a plugged exhaust usually results in a power loss at higher engine rpm, feels like you are running out of fuel, the car will actually decelerate. That said-engine vacuum should not drop to near zero at steady moderate throttle, as long as boost is not being applied; that is characteristic of a plugged exhaust system.Obviously boost will increase the pressure in the intake manifold. It will drop to zero when you stab the throttle, and it should be at it's highest under decel and at idle.

 

Jim,

Have you pulled the cat out at all since the last coule times that header b-pipe gasket has blown out? Perhaps you've got a bunch of old gasket crap blocking the cat filamint. I can come up this weekend probably & help out for awhile

 

sounds like a fuel filter to me...

 

I swapped spark plug wires this morning - didn't fix the problem. I haven't dropped the cat yet, maybe tonight.

 

Seems like you have low vacuum. Do a compression and leakdown test.

Otherwise, remove the unichip and the prelude injectors.
Changing injectors is almost as easy as changing spark plugs.

 

I had a distributor go bad once and it was kinda the same problem. Try a new distributor off of a friends car. I lost about 30 hp with the bad distributor. I also fried a cat once. The car would lose power and stall. It didn't even throw any codes. Just a couple of experiences that I thought I would share.