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Rich spikes cause stumble at cruise

Mbeas96

Mbeas96

Member
Joined
Aug 7, 2017
Location
Charleston
90 745 lh2.4 16t 15psi, chipped computers and a newly installed wideband o2 sensor and gauge.
While cruising at any speed, it usually happens higher, but it will happen anytime while cruising...the afr s are perfect, bouncing between 14.4 and 14.9 but the car will stumble randomly and the AFRs are climbing from at least 10.0. (Aem uego wideband, only reads down to 10).it climbs back to around 15.3ish never higher and then settles back to 14.7ish...

Another issue that might be related...from idle to any kind of real throttle input afrs drop down past 10.0 and the car stumbles for a second. In WOT high rpms it pulls great. Aw71 with the accumulator mod will rip the tires shifting into 2nd. The initial stumble, ive read could be a dead o2, but IIRC that was for a lean spike.

Im not sure how to test anything really as it idles smooth, right at "stoich" and in boost and when boost is rising its great afr s drop down to between 11.9 and 12.8. In later gears high rpm it'll go to 13.1 or so, but that's a different problem.
 
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Well thats awesome to hear those two things might be causing my issue, ive got some t5 391cc injectors along with a dodge 4 bar regulator on the way, but was unsure about switching them till I got this problem solved.
 
Mbeas96 said:
Well thats awesome to hear those two things might be causing my issue, ive got some t5 391cc injectors along with a dodge 4 bar regulator on the way, but was unsure about switching them till I got this problem solved.
Click to expand...

I vote for fixing the current problem before having future compounded issues.
 
So how do you suggest I proceed with deciding if these are my culprits? Get fuel injectors cleaned? Or install newly acquired t5 injectors and keep stock fpr? If my problem isn't gone, swap fpr for another stock fpr, orrrr put dodge 4 bar fpr.
 
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Okay, its been a while, but in still having this same issue. I'd say not as bad, but its always been very interminennt. I have swapped injectors, with t5 ones and I bypassed the resistor pack. I did have a broken cap on one of my old injectors. I also changed the fpr with a "good looking" junkyard Volvo one. I have replaced all the old fuel line on the fuel rail and in the engine bay. The car has had the main in line pump replaced about a year ago.

What could be causing this? I am eager to venture forward in making my car faster...but I dont bigger problems created from smaller ones..
 
I'd check the knock sensor.
Mine did essentially the same. Any load over sustaining up to 60 mph was OK ish with some stumble (rich spike), bad idle, sometimes wot would be fine though rich. Mine ran rich at cruise too.. So that's different.

Who knows. It's an easy part to swap or test. It's a piezo element, infinite resistance on an untouched sensor. If you measure any voltage over its pins short it and check resistance.
It very well be something else. But this knock sensor gave some weird issues on mine!
Mine also had some issues with plugs without resistor.. Had to swap those out too since the spike seemed to cause issues too.
 
I have an known good knock sensor that is on my old engine, wouldn't hurt to swap them around.

Its really not bad, and it doesn't do it very often. In my 60 mile one way trip to work this morning it spiked and stumbled 3, maybe 4 times. Idle is very recently been perfect at around 800 after setting throttle to greenbook specs and adjusting tps. Afrs are perfect at cruise and idle and then rich like they should in higher boost, although to rich right now I suspect it just needs a little more time to learn.
 
back from the dead...its been a while, but I'm still having the same issues. I'm pretty sure I was at least involved in another thread pertaining to a hesitation from idle unless I ease very slowly onto the throttle.

well, again from idle if I ease onto the throttle ever so slightly all is good, but if I press it like a normal person would, I get a quick "misfire" or something to that effect. My AFRs drop to ~11.0 and the car literally almost shuts off. It 99% of the time will catch itself instantly and ill accelerate normally after that. On one or two occasions the car has died, but its been switching between neutral and reverse then throttle press, cuts off.

Also, at cruise I hace a random misfire. happens mostly at 10 in/hg vacuum, (just cruising) but can happen at any point in vacuum.

I have:
Swapped injectors to "cleaned" T5 injectors along with resistor pack bypass
Upgraded to wasted spark to eliminate coil and dist. parts
New plugs and plug wires
Swapped CPS (not sure if it matters, but mine was trash)
Checked coolant system for exhaust gases (blown headgasket) all is good
Replaced knock sensor with 3 different ones. cleaned surfaces, torqued correctly.
Read ohms from ECT sensor at the fuel computer all readings within spec to greenbook.
Made sure TPS is adjusted properly, clicks approx. 2-3mm after opening.
Read voltage of AMM and swapped with a "known good" one.
Measured fuel pressure (in park, revving) and swapped to a different FPR, no gas in vacuum line, and pressure looked good.
Pressure tested system multiple times and found probably 10 leaks, fixed all but one. car runs better and feels better, but my issues are still there. slight leak from cbv is still present.

Edit, oh yeah...put a couple bottles of techron and lucas fuel injector cleaner with a couple tanks of 93 hoping for something from my injectors.

These problems have been lingering for as long as I can remember. Very frustrating to say the least.

although it may mean nothing, it was stumbling while cruising very much this morning, way more than normal. i had messed with the TPS last night to see if I could adjust it to click sooner...well i could not, i could only get it to click about 2 mm after opening. well come to find out, I forgot to plug the TPS back in. no CEL or anything, but my question.

could this be cause by a "BAD" TPS? can they go bad and cause faulty throttle readings even though the click is still present?
 
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On a 740 the TPS only tells the computer when the throttle plate is closed (or not closed). At cruising or anything above idle it has no function.

Sounds to me like signal loss from a sensor (CPS or AMM). A sporatic loss of the power to the fuel system/ECU can wreak such havoc and is often caused by a faulty relay. You're looking for the fuel pump relay and/or radio suppression relay and need to check them for charred contacts and cracked solder joints or just replace with known good units. Otherwise you're going to start having to hunt for bad grounds or faulty leads in the harness...
 
sigh...lol not what I wanted to hear.

I forgot to mention my Fuel pump relay failed at work one day, so I replaced it with another Volvo one, also bought a spare cheap off eBay so ill try that one too.

ill swap the RSR soon and see if theres change.

ill give the AMM a try, but I've cleaned connectors on AMM and connector multiple times
also I have cleaned/re wired all grounds in the engine bay. fuel rail, valve cover, behind both headlights, main battery ground to frame and to engine block

could a failed ECU cause these problems? Sbabbs chips if it matters. same in ezk but along with Buchka wasted spark board
 
also I forgot to add (it was late) I do not have a CEL light, but when the diag box is checked code 2-3-2 too rich or too lean I believe from socket 6. ill check again later.

I can only assume its picking up the random rich misfires

edit. in terrible at remmebering everyting, main pump replaced approximately 20 k miles ago, about 2 years. both pumps turn on, I'm unsure if both are running while car is running
 
well, my RSR harness was not to great.all the "wax" that holds the wires together disintegrated. if it wasn't iffy before it definitely is now. I have a new RSR on the way. but a new harness would be nice.

anybody know if there any available? I bought a ECT harness a while ago, I forget who from.
 
ahh I understand now. sweet, ill pop a new relay in tonight before I drive home, if it still acts up ill address the harness. thanks for the info!
 
well derp...I cant just plug in a new relay that doesnt match the old one. I bought a bosch 4 prong relay and some butt connectors. ill play with it tomorrow and update
 
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