Gonna try again ... Need ideas about hesitation on light throttle

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Gonna try again ... Need ideas about hesitation on light throttle

December 16, 2007, 12:57:34 AM

This will get long, so be patient. After all, I've been hunting the problem for nearly 15 years off and on.

The history of the car (I'm the OO) is ex-wife overheated it when the bypass hose blew, and she couldn't figure out why things were getting all steamy outside. It didn't blow any head gaskets, but did pretty much hose up every other gasket on the engine. From that point on, the engine leaked some kind of fluid from something constantly. I finally gave up because I had no time to do the work myself nor experience with liquid cooled engines, and let a local mechanic replace the timing cover and intake gaskets for me. Well, at least he stopped the leaks at the timing cover. What I found out several years later, is he left a rag in the cam valley under the intake when he put it back on. I found this out the hard way when the oil pressure light came on about half way back from Kentucky. The original engine only had 63000 miles on it. That wound up costing me a long block install by a dealership (again because I had no time nor facilities to do the job myself), only to have to go back on the timing cover again in 14 months. Ennyhoo, got all the leaks stopped (except around the home-made blocking plate [a piece of tin can] for a fuel pump the dealership put on it), and finally got back to trying to find a problem that it's been having since the first overheat in 1991. This is not a new problem with the long block replacment. It hasn't changed a bit, so I'm relatively certain it isn't mechanical. The new engine's got about 30K on it now.

It cranks just fine, idles like a dream, cold or hot. Punch it to WOT, and it does the best a 3.8 can do with CFI. Light throttle, however is a whole new ball game. After it warms up, especially. Normal driving, the car will nose over when you start to move from a stop. Anything below 50 mph, and light throttle, it's like it's running out of fuel. That is NOT the case.

Plugs, wires, cap, rotor, ALL replaced with Motorcraft parts. Excellent spark, judging from the dents I put in it with the back of my head when I accidentally pulled #1 wire off the dizzy hooking up the timing light.

I've checked pressure, using the fuel pump test input and a vacuum pump to operate the FPR, and all is well with pressure regulation, but that doesn't say pressure isn't collapsing when the injectors are actually dumping fuel in the venturis. HOWEVER, if that were the case, I don't think it would jump to life at WOT. I've pulled codes, and it lies and says 11, all is good, both KOEO and KOER. I've tried a new TPS. Blocked off the EGR control valves (threw a code). Disabled vacuum lines to smog pump. You name it, I've tried it, except replacing the ECM.

When I get on the interstate, it'll cruise all day at 75-80 mph, and never miss a beat. When I get off the interstate, and it cools down a bit from the highway ride (about a mile of <45 mph driving), it starts with the hesitation again. Just like the injectors have quit firing or something. It NEVER pings from lean fuel. It never has lean miss backfire. Timing is rock solid at 10 BTDC with spout out, and about 15-16 spout in at idle, jumping up to about 35-37 at WOT kicks. If I hold the throttle steady at 30 mph, it will start surging. Let off, it idles just fine. NEVER stalls at idle. If I rev the engine in park, it runs like a champ, no hesitation. It ONLY has this problem when the car is moving. VSS maybe? Does this vintage of ECM even use VSS?

Everything I test says it's working as it should be, but the extreme hesitation on light throttle is not only annoying, but could be very dangerous in heavy traffic. Just for gins and griggles, I put a new ECT, ACT, and TPS sensors on it. No change on ANY of these replacements. And yes, I did disconnect the battery before starting the process of changing each one so the ECM could relearn everything.

I'm sort of leaning toward yanking the TB and EGR again, and check under the throttle body to see if there's a hole burned in the spacer/gasket where there shouldn't be. I've done it before, though with little or no improvement on the problem. It was gunked up pretty bad, but I've seen worse. The symptoms being absent at WOT and idle, and showing up only when the car is moving strongly suggest an EGR problem. It's not giving me an EGR code, but all that says is the plunger is moving in and out when the ECM says it should be. Doesn't say diddly about the quality of the performance of the EGR. Doesn't the EGR stay closed below a given speed of the vehicle as well? The only purpose of the EGR is to introduce exhaust to displace fuel/air mix to cool combustion temperatures and reduce NOX gas emissions. It also gives a side effect of better fuel economy.

On two occasions, when pulling codes, I can remember getting KAM checksum errors. Is it possible the KAM has 'holes' in it which screws with the injector tables turning off the injectors at times? Normally, memory errors make one go TOTALLY bonkers, well, at least on a PC it does. If I were getting py mileage, I'd lean toward an ECM being in limp mode. But, it runs 16-17 city, and 23-25 highway. Not bad for a C5 tranny (not C3 as the sig says). Don't think I can ask for much better out of an underpowered very heavy car with no overdrive.

The old bird is currently serving as Mrs Paint's daily driver, and I want it to be safer for her. I just can't do anything to take it out of commission until I can get her a new car. (She wants a Dodge Charger). Blasphemy to a Ford enthusiast, but gotta admit it's a sharp lookin car. But, the deal is, if she gets a new Dodge, I get a new F-150 so I can pull the Dodge home when it quits. Guess I could do that just as well with the old F-150.

I love my old Fords, but the old bird has tested my patience on more than one occasion. When I get the new ride for Mrs. Paint, gonna let the kids drive the bird until I can piece together the mods (302 HO, SEFI, MAF, mild cam, and AOD).

Gonna try again ... Need ideas about hesitation on light throttle

Reply #1 – December 16, 2007, 01:55:46 AM

egr will simply recirculate exhaust back into the intake for a reburn cycle. IF you wanna call it good gas mileage adder , then so be it but the egr isnt. Perhaps the movement of the EVP sensor playing a roll in the voltage changes could likely be the "fuel economy" part but certainly not the part just below it called the EGR.

You say you have a CFI but mentioned you used a Vac pump to pull a vac on the FPR. Thats impossible on a CFI car cause the fuel presure is not vac operated. If the FPR atop the CFI has a silver little cap in the middle, it can be drilled and poped out so you gain access to the allen screw to adjust it. You can adjust it using an allen wrench and your fuel pres tester at the shrader valve. I think i figured out 1 turn clockwise = 2psi increase in FP.

So,, im confussed on how the fuel reading was taken and what was going on with your vac pump.

Now,, go to my diy link and fix your hesitation problem. Its in there!!
Remove the CFI, take it apart, remove the injectors and remove the injector screens. Problem solved. They will be collapsed or just plain clogged up.

Argue it all day long if you want,, and when we both are finally blue in the face debating it, you will remove the injector screens,, take it for a spin and thank me later.

Its just that simple,, injector screens are the issue. The car in my sig is the one i hunted down the same problem just as you described. Good on highway, decent on take off but on every takeoff in town with medium throttle, there was this whole momentary "nothing" before something kicked in and fuel took hold.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #2 – December 22, 2007, 12:23:32 PM

Quote from: jcassity;192983

egr will simply recirculate exhaust back into the intake for a reburn cycle. IF you wanna call it good gas mileage adder , then so be it but the egr isnt. Perhaps the movement of the EVP sensor playing a roll in the voltage changes could likely be the "fuel economy" part but certainly not the part just below it called the EGR.

You say you have a CFI but mentioned you used a Vac pump to pull a vac on the FPR. Thats impossible on a CFI car cause the fuel presure is not vac operated. If the FPR atop the CFI has a silver little cap in the middle, it can be drilled and poped out so you gain access to the allen screw to adjust it. You can adjust it using an allen wrench and your fuel pres tester at the shrader valve. I think i figured out 1 turn clockwise = 2psi increase in FP.

So,, im confussed on how the fuel reading was taken and what was going on with your vac pump.

Now,, go to my diy link and fix your hesitation problem. Its in there!!
Remove the CFI, take it apart, remove the injectors and remove the injector screens. Problem solved. They will be collapsed or just plain clogged up.

Argue it all day long if you want,, and when we both are finally blue in the face debating it, you will remove the injector screens,, take it for a spin and thank me later.

Its just that simple,, injector screens are the issue. The car in my sig is the one i hunted down the same problem just as you described. Good on highway, decent on take off but on every takeoff in town with medium throttle, there was this whole momentary "nothing" before something kicked in and fuel took hold.

Me? Argue with YOU? Nope, not gonna happen. Umm, a little embarrassing, but yeah, you're right about the internals on the CFI. Silly me, but I was having fuel/air delivery problems with both the 'Bird and my 5.0 in my F-150 at the same time, and the F-150 is the one I played with using the vacuum pump. They tend to run together when both are nagging you with problems. Turns out, I had a leaking plenum gasket on the F-150, which was causing all sorts of weird problems. Well, maybe just a little argument about EGR function. By displacing intake fuel/air mixture, with exhaust, it DOES stretch the fuel a bit, as well as make the combustion temperatures cooler. This is one reason why engine temps are slightly higher with a plugged up or non-functional EGR, especially on highway driving. Blocking off the EGR on my F-150 while troubleshooting dropped the mileage by a couple mpg on highway mileage, as well as pissed off the O2 sensor, but nothing I didn't expect. By lowering combustion temps, it also reduces NOX emissions. We don't have emissions inspections here, which is probably a good thing, because I'm sure this old car probably wouldn't pass.

I'm looking at pulling the CFI body off anyway. I'm relatively positive that the stealership didn't do so when they did the long-block. (Don't get me started on that story). I'd be willing to bet it's probably chocko full of carbon under there. It's mostly the city run-about for the new Mrs. Paint, so I'm sure it gets LOTS of soot deposits. She typically get in, fires it up, and is in R to back out the driveway before fast idle drops off. If I remember right, the first driveability issues I had with the car was due to carbon build-up under the TB spacer. I can't remember, but can the spool be removed from the EGR for a THOROUGH cleaning? I gotta go in it anyway ....

But, at last, someone finally responded to the same symptoms. This car's been doing this for a VERY long time. I've owned the old bird since brand spankin new. Who knows what kinda the ex ran through it for fuel. I gotta ask though, isn't it a good idea to replace (not just remove) the screens? I know we have filters in line which SHOULD stop anything large enough to foul the injectors, but someone decided those strainers in the injectors were necessary. One symptom that you didn't compare notes to, though is that sometimes, the problem just doesn't seem to exist. I haven't figured out a pattern on it to make me look at one thing specifically though, and I've been trying for YEARS to figure it out. As I said, when I first get off the interstate and the engine's all excited about the good workout it's had, no hesitation until I've driven a couple miles at 40-45, and the temperature drops back down just a bit. Not much temperature difference between city and highway driving, just a little. Best guestimate is about 10 degrees, maybe a needle width on the gauge. The gauges/sensors are non-linear, so it's hard to say how much without a digital gauge. And, when it's cold, when it should be needing the MOST fuel, it doesn't have the problem (longer injector pulses for enrichment preventing the hesitation?). ONLY at operating temperature for normal city driving. But generally speaking, yeah, that NOTHING when starting off, or the stumbling when moving in slow traffic is real annoying, and to me, quite un-safe. I still question, though, why would WOT make it take off like a scalded dog if fuel flow is obstructed/restricted? Does the CFI run at a constant pressure? On the EFI on my 5.0, it reduces the pressure at idle (high vacuum), and increases it based on vacuum level dropping. Is the pulse width to the CFI injectors the ONLY means of controlling fuel flow into the intake?

I'm not arguing what you said about the injectors, and will probably do exactly what you said about yanking the body off and giving it a good cleaning/rebuild. It's the original that came on the car, so I can see why it would be gunked up a bit. It's only been separated from the intake one time that I know about. Now is not a good time, though, with all the obligatory Xmas shopping trips that are compulsory with 4 teens in the house.

I may look into replacing the screens as I did on my F-150 while I'm at it. Only two to do in this case, instead of the 8 I had to do on the truck. Took longer to clean/service the injectors than it did to disassemble/reassemble the entire intake on the 5.0. I guess an alternative would be to grab a CFI body outta a yard and build it up so the swap will go quicker. Just finding a yard with 15+ year old cars in this area is a challenge, though. The price for s steel is too good for them to let old ones sit waiting for someone to need donor parts. We have 3 steel mills (soon to be 4) in this state, so the demand for s is GOOD. That makes the availability of old car parts BAD.

Good time to replace all gaskets and O's too? Gotta disassemble, might be a good idea to have a gasket set handy and just stick it in while doing the job.

How much trouble have you had with erosion of the phenolic spacer? It's been probably 15 years since I had the TB off this thing, but seems I remember some erosion back then. Could be the old '76 Monarch with the 2150 Motorcraft that I'm remembering, though. I just want to be prepared to do ALL of what it needs when I start. Getting time to work on it, and being ready to do the work are things I have to plan very carefully so I don't wind up with a disabled vehicle if I have to drop and run for work. Mrs. Paint won't drive my truck in traffic. Can't say I blame her, especially this time of year. That clutch will give the left leg a severe workout.

Heading for your DIY sticky to read up some more. If I can make this old girl run good, I may postpone the project some until I get a little return on the long-block I bought. Then, she's gonna get a 5.0 dropped in. Nothing hot-rod, just turning it into the car I wanted to start with. Hey, I'm only 21 years late .....

Gonna try again ... Need ideas about hesitation on light throttle

Reply #3 – December 22, 2007, 12:53:18 PM

I won't guarantee that the injector screens are the problem, but I cured similar issues ('85 3.8L C5) by replacing the injectors (I didn't feel like swapping out the screens).

My symptoms were that it would run fine when cold, but once it got warm it would stumble and hesitate if you gave it any more than light throttle. It would be decent for most city driving, but if you ever floored it or rapidly increased throttle it would nose over and stumble like mad - dangerous and disconcerting when making an unprotected left hand turn. After a few seconds it would recover and roar to life. It was just fine on the interstate.

My injector screen got clogged up after I left the fuel lines disconnected for about a week in a parking lot after I replaced the lower CFI-block gasket and dropped a critical fitting into the nether-regions of my fender. Hey, I was a poor college student! The stumble-rama started after I found the fitting and buttoned everything back up. Who knows, maybe some mechanic let the lines get contaminated after fixing things from the overheat.

You've done a very thorough job. If the injectors don't work, I'd probably buy a $50 JY ECU and see if it fixes anything.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #4 – December 23, 2007, 02:39:27 AM

your fuel presure regulator is adjustable

the screens come out easy by starting a screw in the top and yanking out the old screen.

Yes, you could install new injector screens.

there is a gold fitting on the drivers side rear of the cfi that gets carbon buildup. The cfi should come off so you can inspect.

the EGR's EVP sensor does most of the sensing and signals the MAP so you are correct on both a accounts. I just tend to dissagree with the loyalty an egr offers to perfromance.

It would be a good idea to find a donor CFI and take it apart. The four screws on the bottom that allow you to split the CFI in half are fun. Use a torch to heat up the area where the screws pass through and this will melt the loc-tite and make it easier to loosen the screws.

Your fuel delivery is good when you gun the gas because of the voltage ref at the tps. At lighter throttle or sort of 3/4 of the way, hesitation is more likely to show up. The hesitation was always on take off for me so the injector screen removeal cured that. i also chased this problem for years as well.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #5 – December 23, 2007, 03:09:16 PM

Quote

If the injectors don't work, I'd probably buy a $50 JY ECU and see if it fixes anything.

Perhaps upgrade to an '87 specific if you go that route.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #6 – December 24, 2007, 01:31:31 PM

I for one ain't buying the clogged screens since it doesn't do it cold or at WOT...

I had a similar problem with a EFI 2.3 Mustang when the TPS was bad... It never threw a code, but on light throttle it would increase in resistance instead of decrease... Gagging it WOT it ran fine..

Gonna try again ... Need ideas about hesitation on light throttle

Reply #7 – December 24, 2007, 01:48:05 PM

Did you ever set the voltage on the TPS sensor(s)?

Gonna try again ... Need ideas about hesitation on light throttle

Reply #8 – December 25, 2007, 12:42:42 PM

Yup, replaced and set the TPS for 0.9 V at idle. Didn't find anything wrong with the original, and neither has anyone else that's tried to diagnose this problem. To me, it makes more sense for it to strangle the fuel if the screens are clogged at WOT, but, hey, I'm looking for suggestions, here. I'm open to most anything. I've got too much money in the long block to just replace it or give up on it. I've had the TB off before, and yes, it was completely caked up with carbon under the spacer, but that was years ago, and I haven't really done anything to it since the long block install. Well, other than digging around for vac leaks, checking codes, yada yada yada. It's got new cap, rotor, wires, plugs, and trust me, PLENTY spark. Timing's dead on at 10 BTDC. Chain/gears all have less thatn 30K on them (came with the long block). My whole point here is the long block installation eliminated some things for me, cause the ECM and top are still the same.

With a teen age girl at home that constantly wants to go somewhere else, it's seldom cooled off, let alone available for working on. Someone's just going to have to get in line, and right now, that's me and the service work. I may hit the U-Pull-It this week and see if I can get my hands on a CFI that I can rebuild on the bench, and just swap it when I can get a few minutes with the car.

Will the top end off a later model with SEFI (not MAF) fit this block/heads? I'd love to get a little more outta the engine, but don't want to do anything that's going to put it out of commission for weeks while I'm scrounging for that ONE part that I missed getting. I'm on the road a lot in my job, and I need an option that's going to be a weekend job.

Thanks for the replies, guys. Will post when I make a difference, good or bad.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #9 – December 25, 2007, 01:19:10 PM

Quote

With a teen age girl at home that constantly wants to go somewhere else, it's seldom cooled off, let alone available for working on

Pull the rotor. Let her think it's something major:hick:

Gonna try again ... Need ideas about hesitation on light throttle

Reply #10 – December 25, 2007, 08:25:00 PM

When you go to WOT, does it hesitate at all or does it act normally?

Your symptoms seem to indicated a lean condition at light throttle. I'd suspect the EGR, but you have plugged the EGR valve with no difference, so that rules it out. Have you tried backprobing the O2 sensors? This could at least confirm a lean condition to help direct future diagnoses.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #11 – December 25, 2007, 08:34:26 PM

Quote

Will the top end off a later model with SEFI (not MAF) fit this block/heads?

Unfortunately no...you can only use 1984-87 parts on this engine.

Just so you don't feel bad, even I (yes, the guy with the website LOL), am having the same identical problem on my '84 3.8 with new heads: hesitation at anything more than half throttle when the engine is warm. I can ease on into the throttle and it's okay but a little to much gas and the car feels like it wants to stall out. On the highway it's fine. Problem existed before and after the new heads. Timing chain is also good. O2 sensor is fine also. A new IAC and TPS are installed, TPS set to .95 volts. The EGR valve was, according to my mechanic, pretty bad but he cleaned it out well enough and it's working fine now with no codes. The injectors and/or screens make a lot of sense and that's something I'll be exploring in the springtime. Otherwise I've got it narrowed down to the MAP sensor or the EEC-IV module (the latter was a known problem for 1984-85). I haven't ruled out the distributor.

Gonna try again ... Need ideas about hesitation on light throttle

Reply #12 – December 30, 2007, 11:51:21 AM

JeremyB:

No, when I stick my leg down the CFI, it runs like a raped ape. (I have very skinny legs). I've actually c00ched the rears loose on wet pavement doing that in 2nd gear. Not very funny, because the back tries to lead then. If I feather it, it seems like when I let off, it's getting plenty fuel/spark/air, and runs great. I don't have to back off to no-load, just reduce throttle slightly. It'll pick back up for a few seconds, then start fading again.

Sitting still, idling, if it weren't for the nearly non-existant ler, I wouldn't even know the engine was running. WOT, yep, it's WOT. No miss at WOT or idle, so I tend to think ignition/spark is fine.

I'm still planning on hitting the U-Pull-It, and see if I can find a CFI for the 5.0 from a crown vic or something. A slight improvement due to larger body, and gives me one to play with on the bench until it's all clean and shiny and ready to install. Installation will be when I clean the EGR plate and TB spacer.

Eric, your symptoms are sorta opposite of mine. When I first push the throttle down in normal driving, it takes off, THEN goes flat, unless I punch it to WOT. If I hold it steady after getting up to speed, it will start surging. When I let off just a little bit (see comment about feathering the throttle) it's like one or both injectors turns back on or something. Just a very weird problem, that's been nagging at me for a very long time. It never gets worse, but I can't seem to make it better either. (At least with non-invasive procedures).

Gonna try again ... Need ideas about hesitation on light throttle

Reply #13 – December 31, 2007, 02:07:18 PM

I'd like to think I had a similar problem with Cougar A (see my signature), some of the symptoms appear to be similar anyway.

I had no codes and it seemed that everything mechanically was is perfect order.

Nobody has mentioned the TFI-Ignition Module. If the thick film within the module has worn or perhaps deteriorated in an unusal manor, it may just be the culprit. It was in my case.

Just putting it out there...

Definitly let us know what it turns out to be *when* you get it solved

Gonna try again ... Need ideas about hesitation on light throttle

Reply #14 – January 01, 2008, 05:26:25 PM

I would think that a TFI/ICM would cause much worse issues, and really, I don't think it's spark related. The car runs too good on the interstate. Once I get it above 50 mph, it'll cruise for hours and never miss a beat. The ICM IS mounted on the dizzy, though, and this seems to have been a major contention for Ford. It's mounted over on the fender well on my '92 F-150.

I'm probably going to try to hold out until warmer weather, and see what I can find out when I clean the EGR plate, etc. That'll be a good time to go through all the grounds on the EEC, etc.

It's 22 years old, one owner (me), but the ex wasn't very nice to it. I'd love to completely restore it, because I've always loved that car. Interior parts are the hardest to come by, and mechanical parts aren't easy to find either. Seems all the "Auto Recycling Engineers" are crushing anything over 15 years old.